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| 1 ? fn4138.8 hi7191 24-bit, high precision, sigma delta a/d converter the intersil hi7191 is a monol ithic instrumentation, sigma delta a/d converter which operates from 5v supplies. both the signal and reference inputs are fully differential for maximum flexibility and performance. an internal programmable gain instrume ntation amplifier (pgia) provides input gains from 1 to 128 eliminating the need for external pre-amplifiers. the on-demand converter auto-calibrate function is capabl e of removing offset and gain errors existing in external and internal circuitry. the on-board user programmable digital filt er provides over 120db of 60/50hz noise rejection and allows fine tuning of resolution and conversion speed over a wide dynamic range. the hi7190 and hi7191 are functional ly the same device, but the hi7190 has tighter linearity specs. the hi7191 contains a serial i/o port and is compatible with most synchronous transfer formats including both the motorola 6805/11 series spi and intel 8051 series ssr protocols. a sophisticated se t of commands gives the user control over calibration, pgia gain, device selection, standby mode, and several other featur es. the on-chip calibration registers allow the user to read and write calibration data. features ? 20-bit resolution with no missing code ? 0.0015% integral non-linearity (typ) ?20mv to 2.5v full scale input ranges ? internal pgia with gains of 1 to 128 ? serial data i/o interface, spi compatible ? differential analog and reference inputs ? internal or system calibration ? 120db rejection of 60/50hz line noise ? settling time of 4 conversions (max) for a step input ? pb-free plus anneal available (rohs compliant) applications ? process control and measurement ? industrial weight scales ? part counting scales ? laboratory instrumentation ? seismic monitoring ? magnetic field monitoring related literature ? technical brief tb363 ?guidelines for handling and processing moisture sensit ive surface mount devices (smds)? ? tb348 ?hi7190/1 negative full scale error vs conversion frequency? ? an9504 ?a brief intro to sigma delta conversion? ? tb329 ?intersil sigma delta calibration technique? ? an9505 ?using the hi7190 evaluation kit? ? tb331 ?using the hi7190 serial interface? ? an9527 ?interfacing hi7190 to a microcontroller? ? an9532 ?using hi7190 in a multiplexed system? ? an9601 ?using hi7190 with a single +5v supply? ordering information part number part marking temp. range (c) package pkg. dwg. # hi7191ip hi7191ip -40 to 85 20 ld pdip e20.3 hi7191ipz (see note) hi7191ipz -40 to 85 20 ld pdip* (pb-free) e20.3 hi7191ib hi7191ib -40 to 85 20 ld soic m20.3 hi7191ibz (see note) hi7191ibz -40 to 85 20 ld soic (pb-free) m20.3 hi7191ibz-t (see note) hi7191ibz -40 to 85 20 ld soic tape and reel (pb-free) m20.3 hi7190eval evaluation kit note: intersil pb-free plus anneal products employ special pb-free material sets; molding compounds/die attach materials and 100% matte tin plate termination finish, which are rohs compliant and compatible with both snpb and pb-free soldering operations. intersil pb-free products are msl classified at pb-free peak reflow temperatures that meet or exceed the pb-free requirements of ipc/jedec j std-020. *pb-free pdips can be used for th rough hole wave solder processing only. they are not intended for use in reflow solder processing applications. data sheet june 1, 2006 caution: these devices are sensitive to electrosta tic discharge; follow proper ic handling procedures. 1-888-intersil or 1-888-468-3774 | intersil (and design) is a registered trademark of intersil americas inc. copyright ? intersil americas inc. 2003, 2005, 2006. all rights reserved all other trademarks mentioned are the property of their respective owners.
2 fn4138.8 june 1, 2006 pinout hi7191 (pdip, soic) top view functional block diagram 11 12 13 14 15 16 17 18 20 19 10 9 8 7 6 5 4 3 2 1 sclk sdo sdio cs drdy dgnd v rlo av ss v rhi v cm mode reset osc 1 osc 2 sync dv dd agnd av dd v inhi v inlo digital filter ? modulator pgia 1-bit d/a 1 control and serial interface unit control register serial interface unit clock generator av dd transducer burn-out current v inhi v inlo v cm osc 1 osc 2 drdy reset sync cs mode s clk sdio sdo v rhi v rlo reference inputs ? hi7191 3 fn4138.8 june 1, 2006 typical application schematic 10mhz osc 1 osc 2 v rhi v rlo +2.5v av dd +5v 0.1 f v cm v inhi v inlo agnd dv dd dgnd sclk cs drdy sync sdo sdio +5v 4.7 f + 0.1 f 4.7 f + reset input input av ss -5v 0.1 f 4.7 f + data i/o data out sync cs drdy reset 13 17 16 15 12 11 10 9 8 7 14 6 18 5 4 19 2 3 1 mode 20 reference + - r 1 hi7191 4 fn4138.8 june 1, 2006 absolute maximum rati ngs thermal information supply voltage av dd to agnd. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +5.5v av ss to agnd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -5.5v dv dd to dgnd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +5.5v dgnd to agnd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.3v analog input pins. . . . . . . . . . . . . . . . . . . . . . . . . . . . av ss to av dd digital input, output and i/o pins . . . . . . . . . . . . . . dgnd to dv dd esd tolerance (no damage) human body model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .500v machine model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .+100v charged device model. . . . . . . . . . . . . . . . . . . . . . . . . . . . .1000v operating conditions temperature range . . . . . . . . . . . . . . . . . . . . . . . . . . .-40c to 85c thermal resistance (typical, note 1) ja (c/w) pdip package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 soic package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 maximum junction temperature plastic packages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150c maximum storage temperature range . . . . . . . . . . . -65c to 150c maximum lead temperature (soldering, 10s). . . . . . . . . . . . . 300c (soic - lead tips only) caution: stresses above those listed in ?absolute maximum ratings? may cause permanent damage to the device. this is a stress o nly rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. note: 1. ja is measured with the component mounted on a low effective therma l conductivity test board in free air. see tech brief tb379 fo r details. electrical specifications av dd = +5v, av ss = -5v, dv dd = +5v, v rhi = +2.5v, v rlo = agnd = 0v, v cm = agnd, pgia gain = 1, osc in = 10mhz, bipolar input range selected, f n = 10hz parameter test conditions min typ max units system performance integral non-linearity, inl end point line method (notes 3, 5, 6) - 0.0015 0.003 %fs differential non-linearity (note 2) no missing codes to 20-bits lsb offset error, v os (see table 1) - - - - offset error drift v inhi = v inlo (notes 3, 8) - 1 - v/ c full scale error, fse v inhi - v inlo = +2.5v (notes 3, 5, 8, 10) - - - - noise, e n (see table 1) - - - - common mode rejection ratio, cmrr v cm = 0v, v inhi = v inlo from -2v to +2v - 70 - db normal mode 50hz rejection filter notch = 10hz, 25hz, 50hz (note 2) 120 - - db normal mode 60hz rejection filter notch = 10hz, 30hz, 60hz (note 2) 120 - - db step response settling time - 2 4 conversions analog inputs input voltage range unipolar mode (note 9) 0 - v ref v input voltage range bipolar mode (note 9) - v ref -v ref v common mode input range (note 2) av ss -av dd v input leakage current, i in v in = av dd (note 2) - - 1.0 na input capacitance, c in -5.0- pf reference voltage range, v ref (v ref = v rhi - v rlo ) 2.5 - 5 v transducer burn-out current, i bo - 200 - na calibration limits positive full scale ca libration limit - - 1.2(v ref /gain) - negative full scale calibration limit - - 1.2(v ref /gain) - offset calibration limit - - 1.2(v ref /gain) - input span 0.2(v ref /gain) - 2.4(v ref /gain) - digital inputs input logic high voltage, v ih (note 11) 2.0 - - v input logic low voltage, v il --0.8 v hi7191 5 fn4138.8 june 1, 2006 input logic current, i i v in = 0v, +5v - 1.0 10 a input capacitance, c in v in = 0v - 5.0 - pf digital outputs output logic high voltage, v oh i out = -100 a (note 7) 2.4 - - v output logic low voltage, v ol i out = 3ma (note 7) - - 0.4 v output three-state leakage current, i oz v out = 0v, +5v (note 7) -10 1 10 a digital output capacitance, c out -10- pf timing characteristics sclk minimum cycle time, t sclk 200 - - ns sclk minimum pulse width, t sclkpw 50 - - ns cs to sclk precharge time, t pre 50 - - ns drdy minimum high pulse width (notes 2, 7) 500 - - ns data setup to sclk rising edge (write), t dsu 50 - - ns data hold from sclk rising edge (write), t dhld 0- - ns data read access from instruction byte write, t acc (note 7) - - 40 ns read bit valid from sclk falling edge, t dv (note 7) - - 40 ns last data transfer to data ready inactive, t drdy (note 7) - 35 - ns reset low pulse width (note 2) 100 - - ns sync low pulse width (note 2) 100 - - ns oscillator clock frequency (note 2) 0.1 - 10 mhz output rise/fall time (note 2) - - 30 ns input rise/fall time (note 2) - - 1 s power supply characteristics iav dd --1.5ma iav ss --2.0ma idv dd sclk = 4mhz - - 3.0 ma power dissipation, active pd a sb = ?0? - 15 32.5 mw power dissipation, standby pd s sb = ?1? - 5 - mw psrr (note 3) - 70 - db notes: 2. parameter guaranteed by design or ch aracterization, not production tested. 3. applies to both bipolar and unipolar input ranges. 4. these errors can be remov ed by re-calibrating at the desired operating temperature. 5. applies after system calibration. 6. fully differential input signal source is used. 7. see load test circuit, figure 10, r1 = 10k , c l = 50pf. 8. 1 lsb = 298nv at 24 bits for a full scale range of 5v. 9. v ref = v rhi - v rlo. 10. these errors are on the order of the output noise shown in table 1. 11. all inputs except osc 1 . the osc 1 input v ih is 3.5v minimum. electrical specifications av dd = +5v, av ss = -5v, dv dd = +5v, v rhi = +2.5v, v rlo = agnd = 0v, v cm = agnd, pgia gain = 1, osc in = 10mhz, bipolar input range selected, f n = 10hz (continued) parameter test conditions min typ max units hi7191 6 fn4138.8 june 1, 2006 timing diagrams figure 1. data write to hi7191 figure 2. data read from hi7191 figure 3. data read from hi7191 1st bit 2nd bit cs sclk sdio t pre t sclk t dsu t sclkpw t sclkpw t dhld cs sclk sdio sdo t acc 1st bit 2nd bit t dv sclk cs drdy sdio t drdy 8 7 6 5 1 hi7191 7 fn4138.8 june 1, 2006 load test circuit pin descriptions 20 lead dip, soic pin name description 1 sclk serial interface clock. synchroni zes serial data transfers. data is input on the rising edge and output on the falling edge. 2 sdo serial data out. serial data is read from this line when using a 3-wire serial protocol such as the motorola serial peripheral interface. 3 sdio serial data in or out. this line is bidirectional programmable and interfaces directly to the intel standard serial interface using a 2-wire serial protocol. 4cs chip select input. used to select the hi7191 for a serial data transfer cycle. this line can be tied to dgnd. 5 drdy an active low interrupt indicating that a new data word is available for reading. 6 dgnd digital supply ground. 7av ss negative analog power supply (-5v). 8v rlo external reference input. should be negative referenced to v rhi . 9v rhi external reference input. should be positive referenced to v rlo . 10 v cm common mode input. should be set to halfway between av dd and av ss . 11 v inlo analog input lo. negative input of the pgia. 12 v inhi analog input hi. positive input of the pgia. the v inhi input is connected to a current source that can be used to check the condition of an external transducer. this current source is controlled via the control register. 13 av dd positive analog power supply (+5v). 14 agnd analog supply ground. 15 dv dd positive digital supply (+5v). 16 osc 2 used to connect a crystal source between osc 1 and osc 2 . leave open otherwise. 17 osc 1 oscillator clock input for the devic e. a crystal connected between osc 1 and osc 2 will provide a clock to the device, or an external oscillator can drive osc 1 . the oscillator frequency should be 10mhz (typ). 18 reset active low reset pin. used to initialize the hi7191 registers, filter and state machines. 19 sync active low sync input. used to control the synchronization of a number of hi7191s. a logic ?0? initializes the converter. 20 mode mode pin. used to select between synchronous self clocking (mode = 1) or sync hronous external clocking (mode = 0) for the serial port. esd test circuits figure 5a. figure 5b. figure 5. v 1 r 1 c l (includes stray dut capacitance) figure 4. dut human body c esd = 100pf machine model c esd = 200pf r 1 c esd r 1 = 10m r 1 = 10m r 2 r 2 = 1.5k r 2 = 0 v charged device model r 1 r 1 = 1g r 2 r 2 = 1 v dut dielectric hi7191 8 fn4138.8 june 1, 2006 table 1. noise performance with input connected to analog ground hertz snr enob p-p noise ( v) rms noise ( v) hertz snr enob p-p noise ( v) rms noise ( v) gain = 1 gain = 16 10 132.3 21.7 9.8 1.5 10 120.1 19.7 39.8 6.0 25 129.5 21.2 13.6 2.1 25 114.8 18.8 73.4 11.1 30 127.7 20.9 16.6 2.5 30 113.5 18.6 85.1 12.9 50 126.3 20.7 19.5 3.0 50 111.0 18.1 114.4 17.3 60 125.6 20.6 21.2 3.2 60 109.6 17.9 134.0 20.3 100 122.4 20.0 30.7 4.6 100 105.5 17.2 214.8 32.5 250 107.7 17.6 166.7 25.3 250 95.2 15.5 699.1 105.9 500 98.1 16.0 505.3 76.6 500 89.1 14.5 1417.7 214.8 1000 85.7 13.9 2101.8 318.5 1000 83.5 13.6 2686.0 407.0 2000 68.8 11.1 14661.6 2221.4 2000 62.6 10.1 30110.0 4562.1 gain = 2 gain = 32 10 129.2 21.2 14.0 2.1 10 113.2 18.5 88.8 13.5 25 125.7 20.6 20.9 3.2 25 109.0 17.8 142.7 21.6 30 124.5 20.4 24.1 3.7 30 108.2 17.7 157.4 23.8 50 123.4 20.2 27.3 4.1 50 104.7 17.1 235.8 35.7 60 122.5 20.1 30.3 4.6 60 105.0 17.1 227.8 34.5 100 118.1 19.3 50.0 7.6 100 102.3 16.7 310.5 47.0 250 106.1 17.3 199.5 30.2 250 93.4 15.2 861.1 130.5 500 96.9 15.8 580.1 87.9 500 87.1 14.2 1782.7 270.1 1000 84.4 13.7 2435.6 369.0 1000 78.2 12.7 4990.4 756.1 2000 67.8 11.0 16469.7 2495.4 2000 57.0 9.2 57311.1 8683.5 gain = 4 gain = 64 10 125.9 20.6 20.5 3.1 10 106.7 17.4 186.2 28.2 25 123.1 20.1 28.4 4.3 25 102.9 16.8 288.4 43.7 30 121.8 19.9 32.8 5.0 30 101.9 16.6 325.8 49.4 50 119.9 19.6 40.9 6.2 50 98.5 16.1 479.8 72.7 60 119.9 19.6 40.9 6.2 60 98.9 16.1 459.8 69.7 100 116.1 19.0 63.2 9.6 100 96.3 15.7 620.2 94.0 250 105.7 17.3 209.7 31.8 250 85.5 13.9 2133.5 323.3 500 96.6 15.8 597.8 90.6 500 78.1 12.7 5025.0 761.4 1000 84.3 13.7 2469.5 374.2 1000 66.7 10.8 18693.5 2832.3 2000 68.2 11.0 15656.1 2372.1 2000 50.5 8.1 120163.0 18206.5 gain = 8 gain = 128 10 124.7 20.4 23.4 3.5 10 101.1 16.5 356.5 54.0 25 120.6 19.7 37.8 5.7 25 96.0 15.7 638.3 96.7 30 119.2 19.5 44.3 6.7 30 95.2 15.5 704.8 106.8 50 117.5 19.2 53.8 8.2 50 93.2 15.2 882.2 133.7 60 116.8 19.1 58.6 8.9 60 92.2 15.0 996.7 151.0 100 112.1 18.3 100.0 15.2 100 91.4 14.9 1086.6 164.6 250 101.4 16.5 345.2 52.3 250 79.4 12.9 4346.4 658.5 500 95.3 15.5 691.1 104.7 500 71.8 11.6 10439.2 1581.7 1000 83.1 13.5 2838.6 430.1 1000 60.1 9.7 39923.0 6048.9 2000 68.3 11.1 15494.7 2347.7 2000 44.8 7.1 233238.2 35339.1 hi7191 9 fn4138.8 june 1, 2006 definitions integral non-linearity, inl, is the maximum deviation of any digital code from a straight line passing through the endpoints of the transfer function. the endpoints of the transfer function are zero scale (a point 0.5 lsb below the first code transition 000...000 and 000...001) and full scale (a point 0.5 lsb above the last code transition 111...110 to 111...111). differential non-linearity, dnl, is the deviation from the actual difference between midpoi nts and the ideal difference between midpoints (1 lsb) for adjacent codes. if this difference is equal to or more negative than 1 lsb, a code will be missed. offset error, v os , is the deviation of th e first code transition from the ideal input voltage (v in - 0.5 lsb). this error can be calibrated to the order of the noise level shown in table 1. full scale error, fse, is the deviation of the last code transition from the ideal input full scale voltage (v in -+v ref /gain - 1.5 lsb). this error can be calibrated to the order of the noise level shown in table 1. input span, defines the minimum and maximum input voltages the device can handle while still calibrating properly for gain. noise, e n , table 1 shows the peak-to-peak and rms noise for typical notch and -3db frequencies. the device programming was for bipolar input with a v ref of +2.5v. this implies the input range is 5v. the analysis was performed on 100 conversions with the peak-to-peak output noise being the difference between the maximum and minimum readings over a rolling 10 conversion window. the equation to convert the peak-to-peak noise data to enob is: enob = log 2 (v fs /v nrms ) where: v fs = 5v, v nrms = v np-p /cf and cf = 6.6 (imperical crest factor) the noise from the part comes from two sources, the quantization noise from the analog-to-digital conversion process and device noise. device noise (or wideband noise) is independent of gain and essentially flat across the frequency spectrum. quantization noise is ratiometric to input full scale (and hence gain) and its frequency response is shaped by the modulator. looking at table 1, as the cutoff frequency increases the output noise increases. this is due to more of the quantization noise of the part coming through to the output and, hence, the output noise increases with increasing -3db frequencies. for the lower notch settings, the output noise is dominated by the dev ice noise and, hence, altering the gain has little effect on the output noise. at higher notch frequencies, the quantization noise dominates the output noise and, in this case, the output noise tends to decrease with increasing gain. since the output noise comes from two sources, the effective resolution of the device (i.e., the ratio of the inpu t full scale to the output rms noise) does not remain constant with increasing gain or with increasing bandwidth. it is possible to do post-filtering (such as brick wall filtering) on the data to improve the overall resolution for a given -3db frequency and also to further reduce the output noise. circuit description the hi7191 is a monolithic, sigma delta a/d converter which operates from 5v supplies and is intended for measurement of wide dynamic range, low frequency signals. it contains a programmable gain instrumentation amplifier (pgia), sigma delta adc, digital filter, bidirectional serial port (compatible with many industry standard protocols), clock oscillator, and an on-chip controller. the signal and reference inputs are fully differential for maximum flexibility and performance. normally v rhi and v rlo are tied to +2.5v and agnd respectively. this allows for input ranges of 2.5v and 5v when operating in the unipolar and bipolar modes resp ectively (assuming the pgia is configured for a gain of 1). the internal pgia provides input gains from 1 to 128 and eliminates the need for external pre-amplifiers. this means the device will convert signals ranging from 0v to +20mv and 0v to +2.5v when operating in the unipolar mode or signals in the range of 20mv to 2.5v when operating in the bipolar mode. the input signal is continuously sampled at the input to the hi7191 at a clock rate set by the oscillator frequency and the selected gain. this signal then passes through the sigma delta modulator (which includes the pgia) and emerges as a pulse train whose code density contains the analog signal information. the output of the modulator is fed into the sinc 3 digital low pass filter. the fi lter output passes into the calibration block where offset and gain errors are removed. the calibrated data is then coded (2?s complement, offset binary or binary) before being stored in the data output register. the data output register update rate is determined by the first notch fr equency of the digital filter. this first notch frequency is programmed into hi7191 via the control register and has a range of 10hz to 1.953khz which corresponds to -3db frequencies of 2.62hz and 512hz respectively. output data coding on the hi7191 is programmable via the control register. when operating in bipolar mode, data output can be either 2?s complement or offset binary. in unipolar mode output is binary. the drdy signal is used to alert the user that new output data is available. convert ed data is read via the hi7191 serial i/o port which is comp atible with most synchronous hi7191 10 fn4138.8 june 1, 2006 transfer formats including both the motorola 6805/11 series spi and intel 8051 series ssr protocols. data integrity is always maintained at the hi7191 output port. this means that if a data read of conversion n is begun but not finished before the next conversion (con version n + 1) is complete, the drdy line remains active (low) and the data being read is not overwritten. the hi7191 provides many calibration modes that can be initiated at any time by writing to the control register. the device can perform system ca libration where external components are included with the hi7191 in the calibration loop or self-calibration where only the hi7191 itself is in the calibration loop. the on-chip calibration registers are read/write registers which allow the user to read calibration coefficients as well as write previously determined calibration coefficients. circuit operation the analog and digital supplies and grounds are separate on the hi7191 to minimize digital noise coupling into the analog circuitry. nominal supply voltages are av dd = +5v, dv dd = +5v, and av ss = -5v. if the same supply is used for av dd and dv dd it is imperative that the supply is separately decoupled to the av dd and dv dd pins on the hi7191. separate analog and digital ground planes should be maintained on the system board and the grounds should be tied together back at the power supply. when the hi7191 is powered up it needs to be reset by pulling the reset line low. the reset sets the internal registers of the hi7191 as show n in table 2 and puts the part in the bipolar mode with a gain of 1 and offset binary coding. the filter notch of the digital filter is set at 30hz while the i/o is set up for bidirectional i/o ( data is read and written on the sdio line and sdo is three-stated), descending byte order, and msb first data format. a self calibration is performed before the device begins converting. drdy goes low when valid data is available at the output. the configuration of the hi71 91 is changed by writing new setup data to the control register. whenever data is written to byte 2 and/or byte 1 of the control register the part assumes that a critical setu p parameter is being changed which means that drdy goes high and the device is re- synchronized. if the configurat ion is changed such that the device is in any one of the calibration modes, a new calibration is performed before normal conversions continue. if the device is written to the conversion mode, a new calibration is not performed (a new calibration is recommended any time data is written to the control register). in either case, drdy goes low when valid data is available at the output. if a single data byte is written to byte 0 of the control register, the device assumes the gain has not been changed. it is up to the user to re-calibrate the device if the gain is changed in this manner. for this reason it is recommended that the entire c ontrol register be written when changing the gain of the device. this ensures that the part is re-calibrate d (if in a calibration mode) before the drdy output goes low indicating that valid data is available. the calibration registers can be read via the serial interface at any time. however, care must be taken when writing data to the calibration registers. if the hi7191 is internally updating any calibration register the user can not write to that calibration register. see the operational modes section for details on which calibration registers are updated for the various modes. since access to the calibration registers is asynchronous to the conversion process the us er is cautioned that new calibration data may not be used on the very next set of ?valid? data after a calibration register write. it is guaranteed that the new data will take effect on the second set of output data. non-calibrated data can be obtained from the device by writing 000000 (h) to the offset calibration register, 800000 (h) to the positive full scale calibration register, and 800000 (h) to the negative full scale calibration register. this sets the offset correction factor to 0 and the positive and negative gain slope factors to 1. if several hi7191s share a system master clock the sync pin can be used to synchronize their operation. a common sync input to multiple devices will synchronize operation such that all output register s are updated simultaneously. of course the sync pin would normally be activated only after each hi7191 has been calibrated or has had calibration coefficients written to it. the sync pin can also be used to control the hi7191 when an external multiplexer is used with a single hi7191. the sync pin in this application can be used to guarantee a maximum settling time of 3 conversion periods when switching channels on the multiplexer. analog section description figure 6 shows a simplified block diagram of the analog modulator front end of a sigma delta a/d converter. the input signal v in comes into a summing junction (the pgia in this case) where the previous modulator output is subtracted from it. the resulting signal is then integrated and the output table 2. register reset values register value (hex) data output register xxxx (undefined) control register 28b300 offset calibration register self calibration value positive full scale calibration register self calibration value negative full scale calibration register self calibration value hi7191 11 fn4138.8 june 1, 2006 of the integrator goes into the comparator. the output of the comparator is then fed back via a 1-bit dac to the summing junction. the feedback loop forces the average of the fed back signal to be equal to the input signal v in . analog inputs the analog input on the hi7191 is a fully differential input with programmable gain capabilit ies. the input accepts both unipolar and bipolar input signals and gains range from 1 to 128. the common mode range of this input is from av ss to av dd provided that the absolute value of the analog input voltage lies within the power supplies. the input impedance of the hi7191 is dependent upon the modulator input sampling rate and the sampling rate varies with the selected pgia gain. table 3 below shows the sampling rates and input impedances for the different gain settings of the hi7191. note that this table is valid only for a 10mhz master clock. if the input clock frequency is changed then the input impedance will change accordingly. the equation used to calculate the input impedance is: where c in is the nominal input capacitance (8pf) and f s is the modulator sampling rate. bipolar/unipolar input ranges the input on the hi7191 can accept either unipolar or bipolar input voltages. bipolar or unipolar options are chosen by programming the b/u bit of the control register. programming the part for either unipolar or bipolar operation does not change the input signal conditioning. the inputs are differential, and as a result are referenced to the voltage on the v inlo input. for example, if v inlo is +1.25v and the hi7191 is configured for unipolar operation with a gain of 1 and a v ref of +2.5v, the input voltage range on the v inhi input is +1.25v to +3.75v. if v inlo is +1.25v and the hi7191 is configured for bipolar mode with gain of 1 and a v ref of +2.5v, the analog input range on the v inhi input is -1.25v to +3.75v. programmable gain inst rumentation amplifier the programmable gain instrumentation amplifier allows the user to directly interface low le vel sensors and bridges directly to the hi7191. the pgia has 4 selectable gain options of 1, 2, 4, 8 which are implemented by multiple sampling of the input signal. input signals can be gained up further to 16, 32, 64 or 128. these higher gains are implemented in the digital section of the design to maintain a high signal to noise ratio through the front end amplifiers. the gain is digitally programmable in the control register via the serial interface. for optimum pgia performance the v cm pin should be tied to the mid point of the analog supplies. differential reference input the reference inputs of the of the hi7191, v rhi and v rlo , provide a differential referenc e input capability. the nominal differential voltage (v ref = v rhi - v rlo ) is +2.5v and the common mode voltage cab be anywhere between av ss and av dd . larger values of v ref can be used without degradation in performance with the maximum reference voltage being v ref = +5v. smaller values of v ref can also be used but performance will be degraded since the lsb size is reduced. the full scale range of the hi7191 is defined as: and v rhi must always be greater than v rlo for proper operation of the device. the reference inputs provide a high impedance dynamic load similar to the analog inputs and the effective input impedance for the reference inputs can be calculated in the same manner as it is for the analog input impedance. the only difference in the calculation is that c in for the reference inputs is 10.67pf. therefor, the input impedance range for the reference inputs is from 149k in a gain of 8 or higher mode to 833k in the gain of 1 mode. v cm input the voltage at the v cm input is the voltage that the internal analog circuitry is referenced to and should always be tied to the midpoint of the av dd and av ss supplies. this point provides a common mode input voltage for the internal operational amplifiers and must be driven from a low noise, low impedance source if it is not tied to analog ground. failure to do so will result in degraded hi7191 performance. it is recommended that v cm be tied to analog ground when operating off of av dd = +5v and av ss = -5v supplies. v cm also determines the headroom at the upper and lower ends of the power supplies which is limited by the common mode input table 3. effective in put impedance vs gain gain sampling rate (khz) input impedance (m ) 1 78.125 1.6 2 156.25 0.8 4 312.5 0.4 8, 16, 32, 64, 128 625 0.2 pgia integrator comparator v rhi v rlo dac v in + - + - figure 6. simple modulator block diagram z in = 1/(c in x f s ), fsr bipolar = 2 x v ref /gain fsr unipolar = v ref /gain hi7191 12 fn4138.8 june 1, 2006 range where the internal operational amplifiers remain in the linear, high gain region of operation. the hi7191 is designed to have a range of av ss +1.8v < v cm < av dd - 1.8v. exceeding this range on the v cm pin will compromise the device performance. transducer burn-out current source the v inhi input of the hi7191 contains a 500na (typ) current source which can be turned on/o ff via the control register. this current source can be used in checking whether a transducer has burn t-out or become open before attempting to take measurements on that channel. when the current source is turned on an additional offset will be created indicating the presence of a tr ansducer. the current source is controlled by the bo bit (bit 4) in the control register and is disabled on power up. see figure 7 for an applications circuit. digital section description a block diagram of the digital section of the hi7191 is shown in figure 8. this section includes a low pass decimation filter, conversion controller, calib ration logic, serial interface, and clock generator. digital filtering one advantage of digital filtering is that it occurs after the conversion process and can remove noise introduced during the conversion. it can not, however, remove noise present on the analog signal prior to the adc (which an analog filter can). one problem with the modulator/ digital filter combination is that excursions outside the full scale range of the device could cause the modulator and digi tal filter to saturate. this device has headroom built in to the modulator and digital filter which tolerates signal deviations up to 33% outside of the full scale range of the device. if noise spikes can drive the input signal outside of this extended range, it is recommended that an input analog filter is used or the overall input signal level is reduced. low pass decimation filter the digital low-pass filter is a hogenauer (sinc 3 ) decimating filter. this filter was chosen be cause it is a cost effective low pass decimating filter that minimizes the need for internal multipliers and extensive storage and is most effective when used with high sampling or oversampling rates. figure 9 shows the frequency characteristics of the filter where f c is the -3db frequency of the input signal and f n is the programmed notch frequency. the analog modulator sends a one bit data stream to the f ilter at a rate of that is determined by: f modulator = f osc /128 f modulator = 78.125khz for f osc = 10mhz. the filter then converts the serial modulator data into 40-bit words for processing by the hogenauer filter. the data is decimated in the filter at a rate determined by the code word fp10-fp0 (programed by the user into the control register) and the external clock rate. the equation is: f notch = f osc /(512 x code). the control register has 11 bits that select the filter cutoff frequency and the first notch of the filter. the output data update rate is equal to the notch frequency. the notch frequency sets the nyquist sampling rate of the device while the -3db point of the filter determines the frequency spectrum of interest (f s ). the fp bits have a usable range of 10 through 2047 where 10 yields a 1.953khz nyquist rate. the hogenauer filter contains alias components that reflect around the notch frequency. if the spectrum of the frequency of interest reaches the alias component, the data has been aliased and therefore undersampled. filter characteristics please note: we have recently discovered a performance anomaly with the hi7191. the problem occurs when the digital code for the notch filter is programmed within certain frequencies. we believe the error is caused by the calibration logic and the digital v rhi v rlo v inhi v inlo av dd av ss current source hi7191 ratiometric configuration load cell figure 7. burn-out current source circuit modulator output serial i/o sdo sdio sclk cs drdy reset sync osc 2 osc 1 modulator clock digital calibration and control clock generator filter figure 8. digital section block diagram hi7191 13 fn4138.8 june 1, 2006 notch code not the absolute frequency. the error is seen when the user applies mid-scale (0v input, bipolar mode). with this input, the expected digital output should be mid-scale (800000 h ). instead, there is a small probability, of an erroneous negative full scale (000000 h ) output. refer to technical brief tb348 fo r complete details . the fp10 to fp0 bits programmed into the control register determine the cutoff (or notch) frequency of the digital filter. the allowable code range is 00a h . this corresponds to a maximum and minimum cutoff frequency of 1.953khz and 10hz, respectively when operating at a clock frequency of 10mhz. if a 1mhz clock is used then the maximum and minimum cutoff frequencies become 195.3khz and 1hz, respectively. a plot of the (sinx/x) 3 digital filter characteristics is shown in figure 10. this filt er provides greater than 120db of 50hz or 60hz rejection. changing the clock frequency or the programming of the fp bi ts does not change the shape of the filter characteristics, it merely shifts the notch frequency. this low pass digital filter at the output of the converter has an accompanying settling time for step inputs just as a low pass analog filter does. new data takes between 3 and 4 conversion periods to settle and update on the serial port with a conversion period t conv being equal to 1/f n . input filtering the digital filter does not provide rejection at integer multiples of the modulator sa mpling frequency. this implies that there are frequency bands where noise passes to the output without attenuation. for most cases this is not a problem because the high oversampling rate and noise shaping characteristics of the modulator cause this noise to become a small portion of the broadband noise which is filtered. however, if an anti-ali as filter is necessary a single pole rc filter is usually sufficient. if an input filter is used the us er must be careful that the source impedance of the filter is low enough not to cause gain errors in the system. the dc input impedance at the inputs is >1g but it is a dynamic load that changes with clock frequency and selected gain. the input sample rate, also dependent upon clock frequency and gain, determines the allotted time for the input capacitor to charge. the addition of external compone nts may cause the charge time of the capacitor to increase beyond the allotted time. the result of the input not settling to the proper value is a system gain error which can be eliminated by system calibration of the hi7191. clocking/oscillators the master clock into the hi7191 can be supplied by either a crystal connected between the osc 1 and osc 2 pins as shown in figure 10a or a cmos compatible clock signal connected to the osc 1 pin as shown in figure 10b. the input sampling frequency, modulator sampling frequency, filter -3db frequency, output upda te rate, and calibration time are all directly related to the master clock frequency, f osc . for example, if a 1mhz clo ck is used instead of a 10mhz clock, what is normally a 10hz conversion rate becomes a 1hz conversion rate. lowering the clock frequency will also lower the amount of current drawn from the power supplies. please note that the hi7191 spec ifications are written for a 10mhz clock only. operational modes the hi7191 contains several operational modes including calibration modes for cancelling offset and gain errors of both internal and external circuitry. a calibration routine should be initiated whenever there is a change in the ambient operating temperature or supply voltage. calibration should also be initiated if ther e is a change in the gain, filter notch, bipolar, or unipolar input range. non-calibrated data can be obtained from the device by writing 000000 to the offset calibration register, 800000 (h) to the positive full alias band f n f c frequency (hz) amplitude (db) f n f c 2f n 3f n 4f n 0 -20 -40 -60 -80 -100 -120 figure 9. low pass filter frequency characteristics figure 10a. figure 10b. figure 10. oscillator configurations hi7191 osc 1 osc 2 10mhz 16 17 hi7191 osc 1 osc 2 10mhz 16 17 no connection hi7191 14 fn4138.8 june 1, 2006 scale calibration register, and 800000 (h) to the negative full scale calibration regist er. this sets the offset correction factor to 0 and both the positive and negative gain slope factors to 1. the hi7191 offers several different modes of self-calibration and system calibration. for calibration to occur, the on-chip microcontroller must convert th e modulator output for three different input conditions - ?zero-scale,? ?positive full scale,? and ?negative full scale?. with these readings, the hi7191 can null any offset errors and calculate the gain slope factor for the transfer function of the conv erter. it is imperative that the zero-scale calibration be performed before either of the gain calibrations. however, the order of the gain calibrations is not important. the calibration modes are user selectable in the control register by using the md bits (md2-md0) as shown in table 6. drdy will go low indicating that the calibration is complete and there is valid data at the output. conversion mode for conversion mode operation the hi7191 converts the differential voltage between v inhi and v inlo . from switching into this mode it ta kes 3 conversion periods (3 x 1/f n ) for drdy to go low and new data to be valid. no calibration coefficients are generated when operating in conversion mode as data is calibrated using the existing calibration coefficients. self-calibration mode please note: self-calibration is only valid when operating in a gain of one. in addition, the offset and gain errors are not reduced as with the full system calibration. the self-calibration mode is a three step process that updates the offset calibration register, the positive full scale calibration register, and the negative full scale calibration register. in this mode an internal offset calibration is done by disconnecting the external inputs and shorting the inputs of the pgia together. after 3 conversion periods the offset calibration register is updated with the value that corrects any in ternal offset errors. after the offset calibration is completed the positive and negative full scale calibratio n registers are updated. the inputs v inhi and v inlo are disconnected and the external reference is applied across the modulator inputs. the hi7191 then takes 3 conversion cycles to sample the data and update the positive full sc ale calibration register. next the polarity of the reference voltage across the modulator input terminals is reversed and after 3 conversion cycles the negative full scale calibration register is updated. the values stored in the positive and negative full scale calibration registers correct for any internal gain errors in the a/d transfer function. after 3 more conversion cycles the drdy line will activate signaling that the calibration is complete and valid data is present in the data output register. system offset calibration mode the system offset calibration mode is a single step process that allows the user to lump offs et errors of external circuitry and the internal errors of the hi7191 together and null them out. this mode will convert the external differential signal applied to the v in inputs and then store that value in the offset calibration register. the user must apply the zero point or offset voltage to the hi7191 analog inputs and allow the signal to settle before selecting this mode. after 4 conversion periods the drdy line will activate signaling that the calibration is complete and valid data is present in the data output register. system positive full scale calibration mode the system positive full scale calibration mode is a single step process that allows the user to lump gain errors of external circuitry and the internal errors of the hi7191 together and null them out. this mode will convert the external differential signal applied to the v in inputs and stores the converted value in the positive full scale calibration register. the user must apply the +full scale voltage to the hi7191 analog inputs and allow the signal to settle before selecting this mode. after 4 conversion periods the drdy line will activate signaling the calibration is complete and valid data is present in the data output register. system negative full scale calibration mode the system negative full scale calibration mode is a single-step process that allows the user to lump gain errors of external circuitry and the in ternal errors of the hi7191 together and null them out. this mode will convert the external differential signal applied to the v in inputs and stores the converted value in the negative full scale calibration register. the user must apply the -full scale voltage to the hi7191 analog inputs and allow the signal to settle before selecting this mode. after 4 conversion periods the drdy line will activate signaling the calibration is complete and valid data is present in the data output register. table 4. hi7191 operational modes md2 md1 md0 operational mode 0 0 0 conversion 0 0 1 self calibration (gain of 1 only) 0 1 0 system offset calibration 0 1 1 system positive fu ll scale calibration 1 0 0 system negative full scale calibration 1 0 1 system offset/internal gain calibration (gain of 1 only) 1 1 0 system gain calibration 111reserved hi7191 15 fn4138.8 june 1, 2006 system offset/interna l gain calibration mode please note: system offset/internal gain is only valid when operating in a gain of one. in addition, the offset and gain errors are not reduced as with the full system calibration. the system offset/internal gain calibration mode is a single step process that updates the offset calibration register, the positive full scale calibration register, and the negative full scale calibratio n register. first the external differential signal applied to the v in inputs is converted and that value is stored in the offset calibration register. the user must apply the zero point or offset voltage to the hi7191 analog inputs and allow the signal to settle before selecting this mode. after this is completed the positive and negative full scale calibration registers are updated. the inputs v inhi and v inlo are disconnected and the external reference is switched in. the hi7191 then takes 3 conversion cycles to sample the data and update the positive full scale calibration register. next the polarity of the reference voltage across the v inhi and v inlo terminals is reversed and after 3 conversion cycles the negative full calibration register is updated. the values stored in the positive and negative full scale calibration registers correct for any internal gain errors in the a/d transfer function. after 3 more conver sion cycles, the drdy line will activate signaling that the calibr ation is complete and valid data is present in the data output register. system gain calibration mode the gain calibration mode is a single step process that updates the positive and negative full scale calibration registers. this mode will convert the external differential signal applied to the v in inputs and then store that value in the negative full scale ca libration register. then the polarity of the input is reversed internally and another conversion is performed. this conversion result is written to the positive full scale calibration register. the user must apply the +full scale voltage to the hi7191 analog inputs and allow the signal to settle before selecting this mode. after 1 more conversion period the drdy line will activate signaling the calibration is complete and valid data is present in the data output register. reserved this mode is not used in the hi7191 and should not be selected. there is no internal detection logic to keep this condition from being selected and care should be taken not to assert this bit combination. offset and span limits there are limits to the amount of offset and gain which can be adjusted out for the hi7191. for both bipolar and unipolar modes the minimum and maximum input spans are 0.2 x v ref /gain and 1.2 x v ref /gain respectively. in the unipolar mode the offset plus the span cannot exceed the 1.2 x v ref /gain limit. so, if the span is at its minimum value of 0.2 x v ref /gain, the offset must be less than 1 x v ref /gain. in bipolar mode the span is equidistant around the voltage used for the zero scale point. for this mode the offset plus half the span cannot exceed 1.2 x v ref /gain. if the span is at 0.2 x v ref /gain , then the offset can not be greater than 2 x v ref /gain. serial interface the hi7191 has a flexible, sync hronous serial communication port to allow easy interfacing to many industry standard microcontrollers and microproc essors. the serial i/o is compatible with most synchronous transfer formats, including both the motorola 6805/11 spi and intel 8051 ssr protocols. the serial interface is a flexible 2-wire or 3-wire hardware interface where the hi7191 can be configured to read and write on a single bidirectional line (sdio) or configured for writing on sdio and reading on the sdo line. the interface is byte organiz ed with each register byte having a specific address and single or multiple byte transfers are supported. in addition, the interfac e allows flexibility as to the byte and bit access order. that is, the user can specify msb/lsb first bit positioning and can access bytes in ascending/descending order from any byte position. the serial interface allows the user to communicate with 5 registers that control the operation of the device. data output register - a 24-bit, read only register containing the conversion results. control register - a 24-bit, read/writ e register containing the setup and operating modes of the device. offset calibration register - a 24-bit, read/write register used for calibrating the zero po int of the converter or system. positive full scale calibration register - a 24-bit, read/write register used for calibrating the positive full scale point of the converter or system. negative full scale calibration register - a 24-bit, read/write register used for calibrating the negative full scale point of the converter or system. two clock modes are supported. the hi7191 can accept the serial interface clock (sclk) as an input from the system or generate the sclk signal as an output. if the mode pin is logic low the hi7191 is in external clocking mode and the sclk pin is configured as an input. in this mode the user supplies the serial interface clock and all interface timing specifications are synchronous to this input. if the mode pin is logic high the hi7191 is in self-clocking mode and the sclk pin is configured as an output. in self-clocking mode, sclk runs at f sclk = osc 1 /8 and stalls high at byte boundaries. sclk does not have the capability to stall low in this mode. all interface timing specifications are synchronous to the sclk output. hi7191 16 fn4138.8 june 1, 2006 normal operation in self-clocking mode is as follows (see figure 12): cs is sampled low on falling osc 1 edges. the first sclk transition output is delayed 29 osc 1 cycles from the next rising osc 1 . sclk transitions eight times and then stalls high for 28 osc 1 cycles. after this stall period is completed sclk will again transition eight times and stall high. this sequence will repeat continuously while cs is active. the extra osc 1 cycle required when coming out of the cs inactive state is a one clock cycle latency required to properly sample the cs input. note that the normal stall at byte boundaries is 28 osc 1 cycles thus giving a sclk rising to rising edge stall period of 32 osc 1 cycles. the effects of cs on the i/o are different for self-clocking mode (mode = 1) than for external mode (mode = 0). for external clocking mode cs inactive disables the i/o state machine, effectively freezing the state of the i/o cycle. that is, an i/o cycle can be interrupt ed using chip se lect and the hi7191 will continue with that i/o cycle when re-enabled via cs . sclk can continue toggling while cs is inactive. if cs goes inactive during an i/o cycle, it is up to the user to ensure that the state of sclk is identical when reactivating cs as to what it was when cs went inactive. for read operations in external clocking mode, the output will go three-state immediately upon deactivation of cs . for self-clocking mode (mode = 1), the effects of cs are different. if cs transitions high (inactive) during the period when data is being transferred (any non stall time) the hi7191 will complete the data transfer to the byte boundary. that is, once sclk begins the eight transition sequence, it will always complete the eight cycles . if cs remains inactive after the byte has been transferred it will be sampled and sclk will remain stalled high indefinitely. if cs has returned to active low before the data byte transfer period is completed the hi7191 acts as if cs was active during the entire transfer period. it is important to realize that the user can interrupt a data transfer on byte boundaries. that is, if the instruction register calls for a 3 byte transfer and cs is inactive after only one byte has been transferred, the hi7191, when reactivated, will continue with the remaining two bytes before looking for the next instru ction register write cycle. note that the outputs will not go three-state immediately upon cs inactive for read operations in self-clocking mode. in the case of cs going inactive during a read cycle the outputs remain driving until after the last data bit is transferred. in the case of cs inactive during the clock stall time it takes 1 osc 1 cycle plus prop delay (max) for the outputs to be disabled. i/o port pin descriptions the serial i/o port is a bidirectional port which is used to read the data register and read or write the co ntrol register and calibration registers. the port contains two data lines, a synchronous clock, and a status flag. figure 11 shows a diagram of the serial interface lines. sdo - serial data out. data is read from this line using those protocols with separate lines for transmitting and receiving data. an example of such a standard is the motorola serial peripheral interface (spi) using the 68hc05 and 68hc11 family of microcontrollers, or other similar processors. in the case of using bidirectional data transfer on sdio, sdo does not output data and is set in a high impedance state. sdio - serial data in or out. da ta is always written to the device on this line. however, this line can be used as a bidirectional data line. this is done by properly setting up the control register. bidirectional data transfer on this line can be used with intel standard serial interfaces (ssr, mode 0) in mcs51 and mcs96 family of microcontrollers, or other similar processors. sclk - serial clock. the serial clock pin is used to synchronize data to and from the hi7191 and to run the port state machines. in synchronous external clock mode, sclk is configured as an input, is supplied by the user, and can run up to a 5mhz rate. in synchronous self clocking mode, sclk is configured as an output and runs at osc 1 /8. cs - chip select. this signal is an active low input that allows more than one device on the same serial communication lines. the sdo and sdio will go to a high impedance state when this signal is high. if driven high during any communication cycle, that cycle will be suspended until cs reactivation. chip select can be tied low in systems that maintain control of sclk. drdy - data ready. this is an output status flag from the device to signal that the data output register has been updated with the new conversion result. drdy is useful as an edge or level sensitive interrupt signal to a microprocessor or microcontroller. drdy low indicates that new data is available at the data output register. drdy will return high upon completion of a complete data output register read cycle. mode - mode. this input is used to select between synchronous self clocking mode (?1?) or the synchronous external clocking mode (?0?). when this pin is tied to v dd the serial port is configured in the synchronous self clocking mode where the synchronous shift clock (sclk) for the serial port is generated by the hi 7191 and has a frequency of osc 1 /8. when the pin is tied to dgnd the serial port is configured for the synchronous external clocking mode where the synchronous shift clock for the serial port is generated by an external device up to a maximum frequency of 5mhz. chip select sdo sdio sclk cs drdy hi7191 device status bidirectional data data out port clock mode clock mode figure 11. hi7191 serial interface hi7191 17 fn4138.8 june 1, 2006 programming the se rial interface it is useful to think of the hi7191 interface in terms of communication cycles. each communication cycle happens in 2 phases. the first phase of every communication cycle is the writing of an instructio n byte. the second phase is the data transfer as described by the instruction byte. it is important to note that phase 2 of the communication cycle can be a single byte or a multi-byte transfer of data. for example, the 3-byte data output register can be read using one multi-byte communic ation cycle rather than three single-byte communication cycles. it is up to the user to maintain synchronism with respec t to data transfers. if the system processor ?gets lost? th e only way to recover is to reset the hi7191. figure 13 shows both a 2-wire and a 3-wire data transfer. several formats are available for reading from and writing to the hi7191 registers in both t he 2-wire and 3-wire protocols. a portion of these formats is controlled by the cr<2:1> (bd and msb ) bits which control the byte direction and bit order of a data transfer respectively. these two bits can be written in any combination but only the two most useful will be discussed here. the first combination is to reset both the bd and msb bits (bd = 0, msb = 0). this sets up the interface for descending byte order and msb first format. when this combination is used the user should always write the instruction register such that the starting byte is the most significant byte address. for example, read three bytes of dr starting with the most significant byte. the first byte read will be the most significant in msb to lsb format. the next byte will be the next least significant (recall descending byte order) again in msb to lsb order. the last byte will be the next lesser significant byte in msb to lsb order. the entire word was read msb to lsb format. the second combination is to set both the bd and msb bits to 1. this sets up the interface for ascending byte order and lsb first format. when this combination is used the user should always write the instruct ion register such that the starting byte is the least si gnificant byte address. for example, read three bytes of dr starting with the least significant byte. the first byte read will be the least significant in lsb to msb format. the next byte will be the next greater significant (recall ascending byte order) again in lsb to msb order. the last byte will be the next greater significant byte in lsb to msb order. the entire word was read msb to lsb format. after completion of each communication cycle, the hi7191 interface enters a standby mode while waiting to receive a new instruction byte. instruction byte phase the instruction byte phase initiates a data transfer sequence. the processor writes an 8-bit byte (instruction byte) to the instruction register. the instruction byte informs the hi7191 about the data transfer phase activities and includes the following information: ? read or write cycle ? number of bytes to be transferred ? which register and starting byte to be accessed data transfer phase in the data transfer phase, data transfer takes place as set by the instruction register contents. see write operation and read operation sections for detailed descriptions. osc 1 cs sclk 29 33 37 41 45 89 121 125 figure 12. sclk output in self-clocking mode instruction byte data byte 1 data byte 2 data byte 3 instruction data transfer cycle cs sdio figure 13a. 2-wire, 3-byte read or write transfer instruction byte data byte 1 data byte 2 data byte 3 instruction data transfer cycle cs sdio sdo figure 13b. 3-wire, 3-byte read transfer hi7191 18 fn4138.8 june 1, 2006 instruction register the instruction register is an 8- bit register which is used during a communications cycle for setting up read/write operations. r/w - bit 7 of the instruction register determines whether a read or write operation will be done following the instruction byte load. 0 = read, 1 = write. mb1, mb0 - bits 6 and 5 of the instruction register determine the number of bytes that will be accessed following the instruction byte load. see table 5 for the number of bytes to transfer in the transfer cycle. fsc - bit 4 is used to determine whether a positive full scale calibration register i/o transfer (fsc = 0) or a negative full scale calibration register i/o transfer (fsc = 1) is being performed (see table 6). a3, a2, a1, a0 - bits 3 and 2 (a3 and a2) of the instruction register determine which internal register will be accessed while bits 1 and 0 (a1 and a0) determine which byte of that register will be accessed firs t. see table 6 for the address decode. write operation data can be written to the control register, offset calibration register, positive full scale calibration register, and the negative full scale calibration register. write operations are done using the sdio, cs and sclk lines only, as all data is written into the hi7191 via the sdio line even when using the 3-wire conf iguration. figures 14 and 15 show typical write timing diagrams. the communication cycle is st arted by asserting the cs line low and starting the clock from its idle state. to assert a write cycle, during the instruction phase of the communication cycle, the instruction byte shoul d be set to a write transfer (r /w = 1). when writing to the serial port, data is latched into the hi7191 on the rising edge of sclk. data can then be changed on the falling edge of sclk. data can also be changed on the rising edge of sclk due to the 0ns hold time required on the data. this is useful in pipelined applications where the data is latched on the rising edge of the clock. read operation - 3-wire transfer data can be read from the data output register, control register, offset calibration re gister, positive full scale calibration register, and the negative full scale calibration register. when configured in 3-wire transfer mode, read operations are done using the sdio, sdo, cs and sclk lines. all data is read via the sdo line. figures 16 and 17 show typical 3-wire read timing diagrams. the communication cycle is st arted by asserting the cs line and starting the clock from its idle state. to assert a read cycle, during the instruction phase of the communication cycle, the instruction byte should be set to a read transfer (r /w = 0). when reading the serial port, data is driven out of the hi7191 on the falling edge of sclk. data can be registered externally on the next rising edge of sclk. read operation - 2-wire transfer data can be read from the data output register, control register, offset calibration re gister, positive full scale calibration register, and the negative full scale calibration register. when configured in two-wire transfer mode, read operations are done using the sdio, cs and sclk lines. all data is read via the sdio line. figures 18 and 19 show typical 2-wire read timing diagrams. the communication cycle is star ted by asserting the cs line and starting the clock from its idle state. to assert a read cycle, during the instructi on phase of the communication cycle, the instruction byte should be set to a read transfer (r /w = 0). when reading the serial port, data is driven out of the hi7191 on the falling edge of sclk. data can be registered externally on the next rising edge of sclk. msb654321lsb r/w mb1 mb0 fsc a3 a2 a1 a0 table 5. multiple byte access bits mb1 mb0 description 0 0 transfer 1 byte 0 1 transfer 2 bytes 1 0 transfer 3 bytes 1 1 transfer 4 bytes table 6. internal data access decode starting byte fsca3a2a1a0 description x 0000data output register, byte 0 x 0001data output register, byte 1 x 0010data output register, byte 2 x 0100control register, byte 0 x 0101control register, byte 1 x 0110control register, byte 2 x 1000offset cal register, byte 0 x 1001offset cal register, byte 1 x 1010offset cal register, byte 2 0 1100positive full scale cal register, byte 0 0 1101positive full scale cal register, byte 1 0 1110positive full scale cal register, byte 2 1 1100negative full scale cal register, byte 0 1 1101negative full scale cal register, byte 1 1 1110negative full scale cal register, byte 2 hi7191 19 fn4138.8 june 1, 2006 detailed register descriptions data output register the data output register contai ns 24 bits of converted data. this register is a read only register. byte 2 msb22212019181716 d23 d22 d21 d20 d19 d18 d17 d16 byte 1 15 14 13 12 11 10 9 8 d15 d14 d13 d12 d11 d10 d9 d8 byte 0 7654321lsb d7 d6 d5 d4 d3 d2 d1 d0 figure 14. data write cycle, sclk idle low figure 15. data write cycle, sclk idle high figure 16. data read cycle, 3-wire configuration, sclk idle low figure 17. data read cycle, 3-wire configuration, sclk idle high ir write phase data transfer phase - two-byte write cs sclk sdio sdo three-state three-state i0 i1 i2 i3 i4 i5 i6 i7 b0 b1 b2 b3 b4 b5 b6 b7 b8 b9 b10 b11 b12 b13 b14 b15 ir write phase data transfer phase - two-byte write cs sclk sdio sdo i0 i1 i2 i3 i4 i5 i6 i7 b0 b1 b2 b3 b4 b5 b6 b7 b8 b9 b10 b11 b12 b13 b14 b15 three-state three-state data transfer phase - two-byte read cs sclk sdio sdo i0 i1 i2 i3 i4 i5 i6 i7 b0 b1 b2 b3 b4 b5 b6 b7 b8 b9 b10 b11 b12 b13 b14 b15 ir write phase ir write phase data transfe r phase - two-byte read cs sclk sdio sdo i0 i1 i2 i3 i4 i5 i6 i7 b0 b1 b2 b3 b4 b5 b6 b7 b8 b9 b10 b11 b12 b13 b14 b15 hi7191 20 fn4138.8 june 1, 2006 control register the control register contains 24-bits to control the various sections of the hi7191. this regi ster is a read/write register. dc - bit 23 is the data coding bit used to select between two?s complementary and offset binary data coding. when this bit is set (dc = 1) the data in the data output register will be two?s complement. when cleared (dc = 0) this data will be offset binary. when operating in the unipolar mode the output data is available in st raight binary only (the dc bit is ignored). this bit is cleared after a reset is applied to the part. fp10 through fp0 - bits 22 through 12 are the filter programming bits that determine the frequency response of the digital filter. these bits determine the filter cutoff frequency, the position of the first notch and the data rate of the hi7191. the first notch of the filter is equal to the decimation rate and can be determined by the formula: f notch = f osc /(512 x code) where code is the decimal equi valent of the value in fp10 through fp0. the values that can be programmed into these bits are 10 to 2047 decimal, which allows a conversion rate range of 9.54hz to 1.953khz when using a 10mhz clock. changing the filter notch frequency, as well as the selected gain, impacts resolution. the output data rate (or effective conversion time) for the device is equal to the frequency selected for the first notch to the filter. for example, if the first notch of the filter is select ed at 50hz then a new word is available at a 50hz rate or every 20ms. if the first notch is at 1khz a new word is available every 1ms. the settling-time of the converter to a full scale step input change is between 3 and 4 times the data rate. for example, with the first filter notch at 50hz, the worst case settling time to a full scale step input change is 80ms. if the first notch is 1khz, the settling time to a full scale input step is 4ms maximum. the -3db frequency is determined by the programmed first notch frequency according to the relationship: f -3db = 0.262 x f notch . md2 through md0 - bits 11 through 9 are the operational modes of the converter. see table 4 for the operational modes description. after a reset is applied to the part these bits are set to the self calibration mode. b/u - bit 8 is the bipolar/unipolar select bit. when this bit is set the hi7191 is configured for bipolar operation. when this bit is reset the part is in unipolar mode. this bit is set after a reset is applied to the part. figure 18. data read cycle, 2-wire configuration, sclk idle low figure 19. data read cycle, 2-wire configuration, sclk idle high three-state three-state ir write phase data transfer phase - two-byte read cs sclk sdio sdo i0 i1 i2 i3 i4 i5 i6 i 7 b0 b1 b2 b3 b4 b5 b6 b7 b8 b9 b10 b11 b12 b13 b14 b15 three-state three-state ir write phase data transfer phase - two-byte read cs sclk sdio sdo i0 i1 i2 i3 i4 i5 i6 i 7 b0 b1 b2 b3 b4 b5 b6 b7 b8 b9 b10 b11 b12 b13 b14 b15 byte 2 msb22212019181716 dc fp10 fp9 fp8 fp7 fp6 fp5 fp4 byte 1 15 14 13 12 11 10 9 8 fp3 fp2 fp1 fp0 md2 md1 md0 b/u byte 0 7654321lsb g2 g1 g0 bo sb bd msb sdl hi7191 21 fn4138.8 june 1, 2006 g2 through g0 - bits 7 through 5 select the gain of the input analog signal. the gain is accomplished through a programmable gain instrumentat ion amplifier that gains up incoming signals from 1 to 8. this is achieved by using a switched capacitor voltage mult iplier network preceding the modulator. the higher gains (i.e., 16 to 128) are achieved through a combination of a pgia gain of 8 and a digital multiply after the digital filter (see table 7). the gain will affect noise and signal to no ise ratio of t he conversion. these bits are cleared to a gain of 1 (g2, g1, g0 = 000) after a reset is applied to the part. bo - bit 4 is the transducer burn-out current source enable bit. when this bit is set (bo = 1) the burn-out current source connected to v inhi internally is enabled. this current source can be used to detect the presence of an external connection to v inhi . this bit is cleared after a reset is applied to the part. sb - bit 3 is the standby mode enable bit used to put the hi7191 in a lower power/standby mode. when this bit is set (sb = 1) the filter nodes are halted, the drdy line is set high and the modulator clock is disabled. when this bit is cleared the hi7191 begins operation as described by the contents of the control register. for example, if the control register is programmed for self calibration mode and a notch frequency to 10hz, the hi7191 will perform the self calibration before providing the data at the 10hz rate. this bit is cleared after a reset is applied to the part. bd - bit 2 is the byte direction bit used to select the multi- byte access ordering. the bit determines the either ascending or descending order access for the multi-byte registers. when set (bd = 1) the user can access multi-byte registers in ascending byte order and when cleared (bd = 0) the multi-byte registers are accessed in descending byte order. this bit is cleared after a reset is applied to the part. msb - bit 1 is used to select whether a serial data transfer is msb or lsb first. this bit allows the user to change the order that data can be transm itted or received by the hi7191. when this bit is cleared (msb = 0) the msb is the first bit in a serial data transfer. if set (msb = 1), the lsb is the first bit transferred in the serial data stream. this bit is cleared after a reset is applied to the part. sdl - bit 0 is the serial data line control bit. this bit selects the transfer protocol of the serial interface. when this bit is cleared (sdl = 0), both read and write data transfers are done using the sdio line. when set (sdl = 1), write transfers are done on the sdio line and read transfers are done on the sdo line. this bi t is cleared after a reset is applied to the part. reading the data output register the hi7191 generates an active low interrupt (drdy ) indicating valid conversion results are available for reading. at this time the data output r egister contains the latest conversion result available from the hi7191. data integrity is maintained at the serial output port but it is possible to miss a conversion result if the data output register is not read within a given period of time. maintaining data integrity means that if a data output register read of conversion n is begun but not finished before the next conversion (conversion n + 1) is complete, the drdy line remains active low and the data being read is not overwritten. in addition to the data output register, the hi7191 has a one conversion result storage buffer. no conversion results will be lost if the following constraints are met. 1) a data output register r ead cycle is started for a given conversion (conversion x) 1/f n - (128*1/f osc ) after drdy initially goes active low. failu re to start the read cycle may result in conversion x + 1 data overwriting conversion x results. for example, with f osc = 10mhz, f n = 2khz, the read cycle must start within 1/2000 - 128(1/10 6 ) = 487 s after drdy went low. 2) the data output register read cycle for conversion x must be completed within 2(1/f n )-1440(1/f osc ) after drdy initially goes active low. if the read cycle for conversion x is not complete within this time the re sults of conversion x + 1 are lost and results from conversion x + 2 are now stored in the data output word buffer. completing the data output regi ster read cycle inactivates the drdy interrupt. if the one word data output buffer is full when this read is complete this data will be immediately transferred to the data output register and a new drdy interrupt will be issued after the minimum drdy pulse high time is met. writing the control register if data is written to byte 2 and/or byte 1 of the control register the drdy output is taken high and the device re-calibrates if written to a calibration mode. this action is taken because it is assumed that by writing byte 2 or byte 1 that the user either reprogrammed the filter or changed modes of the part. however, if a single data byte is written to byte 0, it is assumed that the gain has not been changed. it is up to the user to re- calibrate the hi7191 after the gain has been changed by this method. it is recommended that t he entire control register be written to when changing the selected gain. this ensures that the part is re-calibrated before the drdy signal goes low indicating valid data is available. table 7. gain select bits g2 g1 g0 gain gain achieved 0 0 0 1 pgia = 1, filter multiply = 1 0 0 1 2 pgia = 2, filter multiply = 1 0 1 0 4 pgia = 4, filter multiply = 1 0 1 1 8 pgia = 8, filter multiply = 1 1 0 0 16 pgia = 8, filter multiply = 2 1 0 1 32 pgia = 8, filter multiply = 4 1 1 0 64 pgia = 8, filter multiply = 8 1 1 1 128 pgia = 8, filter multiply = 16 hi7191 22 fn4138.8 june 1, 2006 offset calibration register the offset calibration register is a 24-bit register containing the offset correction factor. this register is indeterminate on power-up but will contain a self calibration correction value after a reset has been applied. the offset calibration register holds the value that corrects the filter output data to all 0?s when the analog input is 0v. positive full scale calibration register the positive full scale calibration register is a 24-bit register containing the positive full scale correction coefficient. this coefficient is used to determine the positive gain slope factor. this register is indeterminate on power-up but will contain a self calibration correction coefficient after a reset has been applied. negative full scale calibration register the negative full scale calibr ation register is a 24-bit register containing the negative full scale correction coefficient. this coefficient is used to determine the negative gain slope factor. this register is indeterminate on power-up but will contain a self calibration correction coefficient after a reset has been applied. byte 2 msb22212019181716 o23 o22 o21 o20 o19 o18 o17 o16 byte 1 15 14 13 12 11 10 9 8 o15 o14 o13 o12 o11 o10 o9 o8 byte 0 7654321lsb o7 o6 o5 o4 o3 o2 o1 o0 byte 2 msb22212019181716 p23 p22 p21 p20 p19 p18 p17 p16 byte 1 15 14 13 12 11 10 9 8 p15 p14 p13 p12 p11 p10 p9 p8 byte 0 7654321lsb p7 p6 p5 p4 p3 p2 p1 p0 byte 2 msb22212019181716 n23 n22 n21 n20 n19 n18 n17 n16 byte 1 15 14 13 12 11 10 9 8 n15 n14 n13 n12 n11 n10 n9 n8 byte 0 7654321lsb n7 n6 n5 n4 n3 n2 n1 n0 hi7191 23 fn4138.8 june 1, 2006 die characteristics die dimensions: 3550 m x 6340 m metallization: type: alsicu thickness: metal 2, 16k ? metal 1, 6k ? substrate potential (powered up): av ss passivation: type: sandwich thickness: nitride 8k ? usg 1k ? metallization mask layout hi7191 sclk sdo sdio cs drdy dgnd av ss v rlo v rhi v cm v inlo v inhi av dd mode sync reset agnd dv dd osc 2 osc 1 hi7191 24 fn4138.8 june 1, 2006 hi7191 dual-in-line plastic packages (pdip) notes: 1. controlling dimensions: inch. in case of conflict between english and metric dimensions, the inch dimensions control. 2. dimensioning and tolerancing per ansi y14.5m - 1982. 3. symbols are defined in the ?mo series symbol list? in section 2.2 of publication no. 95. 4. dimensions a, a1 and l are measured with the package seated in jedec seating plane gauge gs - 3. 5. d, d1, and e1 dimensions do not include mold flash or protrusions. mold flash or protrusions shal l not exceed 0.010 inch (0.25mm). 6. e and are measured with the leads constrained to be perpen- dicular to datum . 7. e b and e c are measured at the lead tips with the leads uncon- strained. e c must be zero or greater. 8. b1 maximum dimensions do not include dambar protrusions. dam- bar protrusions shall not exceed 0.010 inch (0.25mm). 9. n is the maximum number of terminal positions. 10. corner leads (1, n, n/2 and n/2 + 1) for e8.3, e16.3, e18.3, e28.3, e42.6 will have a b1 dimension of 0.030 - 0.045 inch (0.76 - 1.14mm). e a -c- c l e e a c e b e c -b- e1 index 12 3 n/2 n area seating base plane plane -c- d1 b1 b e d d1 a a2 l a1 -a- 0.010 (0.25) c a m bs e20.3 (jedec ms-001-ad issue d) 20 lead dual-in-line plastic package symbol inches millimeters notes min max min max a- 0.210 - 5.33 4 a1 0.015 - 0.39 -4 a2 0.115 0.195 2.93 4.95 - b 0.014 0.022 0.356 0.558 - b1 0.045 0.070 1.55 1.77 8 c 0.008 0.014 0.204 0.355 - d 0.980 1.060 24.89 26.9 5 d1 0.005 - 0.13 -5 e 0.300 0.325 7.62 8.25 6 e1 0.240 0.280 6.10 7.11 5 e 0.100 bsc 2.54 bsc - e a 0.300 bsc 7.62 bsc 6 e b - 0.430 - 10.92 7 l 0.115 0.150 2.93 3.81 4 n20 209 rev. 0 12/93 25 all intersil u.s. products are manufactured, asse mbled and tested utilizing iso9000 quality systems. intersil corporation?s quality certifications ca n be viewed at www.intersil.com/design/quality intersil products are sold by description only. intersil corpor ation reserves the right to make changes in circuit design, soft ware and/or specifications at any time without notice. accordingly, the reader is cautioned to verify that data sheets are current before placing orders. information furnishe d by intersil is believed to be accurate and reliable. however, no responsibility is assumed by intersil or its subsidiaries for its use; nor for any infringements of paten ts or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of intersil or its subsidiari es. for information regarding intersil corporation and its products, see www.intersil.com fn4138.8 june 1, 2006 hi7191 small outline plast ic packages (soic) notes: 1. symbols are defined in the ?mo series symbol list? in section 2.2 of publication number 95. 2. dimensioning and tolerancing per ansi y14.5m - 1982. 3. dimension ?d? does not include mold flash, protrusions or gate burrs. mold flash, protrusion and gate burrs shall not exceed 0.15mm (0.006 inch) per side. 4. dimension ?e? does not include interlead flash or protrusions. interlead flash and protrusions shall not exceed 0.25mm (0.010 inch) per side. 5. the chamfer on the body is optional. if it is not present, a visual index feature must be located within the crosshatched area. 6. ?l? is the length of terminal for soldering to a substrate. 7. ?n? is the number of terminal positions. 8. terminal numbers are shown for reference only. 9. the lead width ?b?, as measured 0.36mm (0.014 inch) or greater above the seating plane, shall not exceed a maximum value of 0.61mm (0.024 inch) 10. controlling dimension: millimeter. converted inch dimensions are not necessarily exact. index area e d n 123 -b- 0.25(0.010) c a m b s e -a- l b m -c- a1 a seating plane 0.10(0.004) h x 45 c h 0.25(0.010) b m m m20.3 (jedec ms-013-ac issue c) 20 lead wide body small outline plastic package symbol inches millimeters notes min max min max a 0.0926 0.1043 2.35 2.65 - a1 0.0040 0.0118 0.10 0.30 - b 0.014 0.019 0.35 0.49 9 c 0.0091 0.0125 0.23 0.32 - d 0.4961 0.5118 12.60 13.00 3 e 0.2914 0.2992 7.40 7.60 4 e 0.050 bsc 1.27 bsc - h 0.394 0.419 10.00 10.65 - h 0.010 0.029 0.25 0.75 5 l 0.016 0.050 0.40 1.27 6 n20 207 0 8 0 8 - rev. 2 6/05 |
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