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| a 2.7 V to 5.25 V, Micropower, 8-Channel, 125 kSPS, 12-Bit ADC in 16-Lead TSSOP AD7888 FUNCTIONAL BLOCK DIAGRAM AIN1 AIN8 2.5V REF REF IN/REF OUT BUF FEATURES Specified for VDD of 2.7 V to 5.25 V Flexible Power/Throughput Rate Management Shutdown Mode: 1 A Max Eight Single-Ended Inputs Serial Interface: SPITM/QSPITM/MICROWIRETM/DSP Compatible 16-Lead Narrow SOIC and TSSOP Packages APPLICATIONS Battery-Powered Systems (Personal Digital Assistants, Medical Instruments, Mobile Communications) Instrumentation and Control Systems High-Speed Modems AD7888 I/P MUX T/H VDD COMP CHARGE REDISTRIBUTION DAC SAR + ADC CONTROL LOGIC GENERAL DESCRIPTION AGND SPORT AGND The AD7888 is a high speed, low power, 12-bit ADC that operates from a single 2.7 V to 5.25 V power supply. The AD7888 is capable of a 125 kSPS throughput rate. The input track-andhold acquires a signal in 500 ns and features a single-ended sampling scheme. The AD7888 contains eight single-ended analog inputs, AIN1 through AIN8. The analog input on each of these channels is from 0 to VREF. The part is capable of converting full power signals up to 2.5 MHz. The AD7888 features an on-chip 2.5 V reference that can be used as the reference source for the A/D converter. The REF IN/REF OUT pin allows the user access to this reference. Alternatively, this pin can be overdriven to provide an external reference voltage for the AD7888. The voltage range for this external reference is from 1.2 V to VDD. CMOS construction ensures low power dissipation of typically 2 mW for normal operation and 3 W in power-down mode. The part is available in a 16-lead narrow body small outline (SOIC) and a 16-lead thin shrink small outline (TSSOP) package. CS DIN DOUT SCLK PRODUCT HIGHLIGHTS 1. Smallest 12-bit 8-channel ADC; 16-lead TSSOP is the same area as an 8-lead SOIC and less than half the height. 2. Lowest Power 12-bit 8-channel ADC. 3. Flexible power management options including automatic power-down after conversion. 4. Analog input range from 0 V to VREF (VDD). 5. Versatile serial I/O port (SPI/QSPI/MICROWIRE/DSP Compatible). SPI and QSPI are trademarks of Motorola, Inc. MICROWIRE is a trademark of National Semiconductor Corporation. REV. B Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 www.analog.com Fax: 781/326-8703 (c) Analog Devices, Inc., 2001 5.25 REFIN/REFOUT AD7888-SPECIFICATIONST =(VT =to2.7T V tounlessV,otherwise noted.)= 2.5 V External/Internal Reference unless otherwise noted; f = 2 MHz (V = 2.7 V to 5.25 V); , DD SCLK DD A MIN MAX Parameter DYNAMIC PERFORMANCE Signal to Noise + Distortion Ratio2, 3 (SNR) Total Harmonic Distortion2 (THD) Peak Harmonic or Spurious Noise2 Intermodulation Distortion2 (IMD) Second Order Terms Third Order Terms Channel-to-Channel Isolation2 Full Power Bandwidth DC ACCURACY Resolution Integral Nonlinearity2 Differential Nonlinearity2 Offset Error Offset Error Match2 Gain Error2 Gain Error Match2 ANALOG INPUT Input Voltage Ranges Leakage Current Input Capacitance REFERENCE INPUT/OUTPUT REFIN Input Voltage Range Input Impedance REFOUT Output Voltage REFOUT Tempco LOGIC INPUTS Input High Voltage, VINH Input Low Voltage, VINL Input Current, IIN Input Capacitance, CIN4 LOGIC OUTPUTS Output High Voltage, VOH Output Low Voltage, VOL Floating-State Leakage Current Floating-State Output Capacitance5 Output Coding CONVERSION RATE Throughput Time Track/Hold Acquisition Time2 Conversion Time A Version 71 -80 -80 -78 -78 -80 2.5 12 2 2 6 4.5 2 2 3 0 to VREF 1 38 4 2.5/VDD 5 2.45/2.55 50 2.4 2.1 0.8 10 10 1 B Version 71 -80 -80 -78 -78 -80 2.5 12 1 -1/+1.5 6 4.5 2 2 3 0 to VREF 1 38 4 2.5/VDD 5 2.45/2.55 50 2.4 2.1 0.8 10 10 1 Unit dB typ dB typ dB typ dB typ dB typ dB typ MHz typ Bits LSB max LSB max LSB max LSB max LSB typ LSB max LSB max Volts A max pF typ pF typ V min/max k typ V min/max ppm/C typ V min V min V max A max pF max Test Condition/Comment fIN = 10 kHz Sine Wave, fSAMPLE = 125 kSPS fIN = 10 kHz Sine Wave, fSAMPLE = 125 kSPS fIN = 10 kHz Sine Wave, fSAMPLE = 125 kSPS fa = 9.983 kHz, fb = 10.05 kHz, fSAMPLE = 125 kSPS fa = 9.983 kHz, fb = 10.05 kHz, fSAMPLE = 125 kSPS fIN = 25 kHz @ 3 dB Any Channel Guaranteed No Missed Codes to 11 Bits (A Grade) Guaranteed No Missed Codes to 12 Bits (B Grade) VDD = 4.75 V to 5.25 V (Typically 3 LSB) VDD = 2.7 V to 3.6 V (Typically 2 LSB) Typically 30 LSB with Internal Reference When in Track When in Hold Functional from 1.2 V Very High Impedance If Internal Reference Disabled VDD = 4.75 V to 5.25 V VDD = 2.7 V to 3.6 V VDD = 2.7 V to 5.25 V Typically 10 nA, VIN = 0 V or VDD VDD - 0.5 VDD - 0.5 0.4 0.4 10 10 10 10 Straight (Natural) Binary 16 1.5 14.5 16 1.5 14.5 V min V max A max pF max ISOURCE = 200 A VDD = 2.7 V to 5.25 V ISINK = 200 A SCLK Cycles SCLK Cycles SCLK Cycles Conversion Time + Acquisition Time. 125 kSPS with 2 MHz Clock 7.25 s (2 MHz Clock) -2- REV. B AD7888 Parameter POWER REQUIREMENTS VDD IDD Normal Mode5 (Static) Normal Mode (Operational) Using Standby Mode Using Shutdown Mode Standby Mode6 Shutdown Mode6 Normal-Mode Power Dissipation Shutdown Power Dissipation Standby Power Dissipation A Version 2.7/5.25 700 700 450 80 12 200 2 1 3.5 2.1 10 3 1 600 1 B Version 2.7/5.25 700 700 450 80 12 200 2 1 3.5 2.1 10 3 1 600 1 Unit V min/max A max A typ A typ A typ A typ A max A max A max mW max mW max W max W max mW max W max Test Condition/Comment fSAMPLE = 125 kSPS fSAMPLE = 50 kSPS fSAMPLE = 10 kSPS fSAMPLE = 1 kSPS VDD = 2.7 V to 5.25 V VDD = 4.75 V to 5.25 V (0.5 A typ) VDD = 2.7 V to 3.6 V VDD = 5 V VDD = 3 V VDD = 5 V VDD = 3 V VDD = 5 V VDD = 3 V NOTES 1 Temperature ranges as follows: A Version: -40C to +105C; B Version: -40C to +105C. 2 See Terminology. 3 SNR calculation includes distortion and noise components. 4 Sample tested @ 25C to ensure compliance. 5 All digital inputs @ GND except CS @ VDD. No load on the digital outputs. Analog inputs @ GND. 6 SCLK @ GND when SCLK off. All digital inputs @ GND except for CS @ VDD. No load on the digital outputs. Analog inputs @ GND. Specifications subject to change without notice. ABSOLUTE MAXIMUM RATINGS 1 (TA = 25C unless otherwise noted) ORDERING GUIDE Linearity Error Package (LSB)1 Description 2 1 2 1 SOIC SOIC TSSOP TSSOP Package Option R-16A R-16A RU-16 RU-16 VDD to AGND . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 V to +7 V Analog Input Voltage to AGND . . . . . -0.3 V to VDD + 0.3 V Digital Input Voltage to AGND . . . . . . -0.3 V to VDD + 0.3 V Digital Output Voltage to AGND . . . . -0.3 V to VDD + 0.3 V REFIN/REFOUT to AGND . . . . . . . . -0.3 V to VDD + 0.3 V Input Current to Any Pin Except Supplies2 . . . . . . . . 10 mA Operating Temperature Range Commercial (A Version) . . . . . . . . . . . . . . . . . . . . . . -40C to +105C (B Version) . . . . . . . . . . . . . . . . . . . . . . . 0C to +105C Storage Temperature Range . . . . . . . . . . . -65C to +150C Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . 150C SOIC, TSSOP Package, Power Dissipation . . . . . . . . 450 mW JA Thermal Impedance . . . . . . . . . . . . 124.9C/W (SOIC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150.4C/W (TSSOP) JC Thermal Impedance . . . . . . . . . . . . . 42.9C/W (SOIC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27.6C/W (TSSOP) Lead Temperature, Soldering Vapor Phase (60 secs) . . . . . . . . . . . . . . . . . . . . . . 215C Infrared (15 secs) . . . . . . . . . . . . . . . . . . . . . . . . . 220C ESD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 kV NOTES 1 Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those listed in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. 2 Transient currents of up to 100 mA will not cause SCR latch-up. Model AD7888AR AD7888BR AD7888ARU AD7888BRU EVAL-AD7888CB2 EVAL-CONTROL BRD23 NOTES 1 Linearity error here refers to integral linearity error. 2 This can be used as a stand-alone evaluation board or in conjunction with the EVAL-CONTROL BOARD for evaluation/demonstration purposes. 3 This board is a complete unit allowing a PC to control and communicate with all Analog Devices evaluation boards ending in the CB designators. CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the AD7888 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high-energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. WARNING! ESD SENSITIVE DEVICE REV. B -3- AD7888 TIMING SPECIFICATIONS1 (T = T A MIN to TMAX, unless otherwise noted) Parameter fSCLK tCONVERT tACQ t1 t2 3 t3 3 t4 t5 t6 t7 t8 4 t9 2 Limit at TMIN, TMAX (A, B Versions) 4.75 V to 5.25 V 2.7 V to 3.6 V 2 14.5 tSCLK 1.5 tSCLK 10 30 75 20 20 0.4 tSCLK 0.4 tSCLK 80 5 2 14.5 tSCLK 1.5 tSCLK 10 60 100 20 20 0.4 tSCLK 0.4 tSCLK 80 5 Unit MHz max Description ns min ns max ns max ns min ns min ns min ns min ns max s typ Throughput Time = tCONVERT + tACQ = 16 tSCLK CS to SCLK Setup Time Delay from CS until DOUT 3-State Disabled Data Access Time after SCLK Falling Edge Data Setup Time Prior to SCLK Rising Edge Data Valid to SCLK Hold Time SCLK High Pulsewidth SCLK Low Pulsewidth CS Rising Edge to DOUT High Impedance Power-Up Time from Shutdown NOTES 1 Sample tested at 25C to ensure compliance. All input signals are specified with tr = tf = 5 ns (10% to 90% of V DD) and timed from a voltage level of 1.6 V. 2 Mark/Space ratio for the SCLK input is 40/60 to 60/40. See Serial Interface section. 3 Measured with the load circuit of Figure 1 and defined as the time required for the output to cross 0.8 V or 2.4 V with V DD = 5 V 10% and time for an output to cross 0.4 V or 2.0 V with V DD = 3 V 10%. 4 t8 is derived from the measured time taken by the data outputs to change 0.5 V when loaded with the circuit of Figure 1. The measured number is then extrapolated back to remove the effects of charging or discharging the 50 pF capacitor. This means that the time, t 8, quoted in the timing characteristics is the true bus relinquish time of the part and is independent of the bus loading. Specifications subject to change without notice. 200 A IOL TO OUTPUT PIN 1.6V CL 50pF 200 A IOH Figure 1. Load Circuit for Digital Output Timing Specifications -4- REV. B AD7888 PIN CONFIGURATIONS SOIC AND TSSOP CS 1 16 SCLK 15 DOUT 14 DIN REF IN/REF OUT 2 VDD 3 AGND 4 AD7888 TOP VIEW 13 AGND AIN1 5 (Not to Scale) 12 AIN8 AIN2 6 AIN3 7 AIN4 8 11 AIN7 10 AIN6 9 AIN5 PIN FUNCTION DESCRIPTIONS Pin No. 1 2 Mnemonic CS REF IN/REF OUT Function Chip Select. Active low logic input. This input provides the dual function of initiating conversions on the AD7888 and also frames the serial data transfer. Reference Input/Output. The on-chip reference is available on this pin for use external to the AD7888. Alternatively, the internal reference can be disabled and an external reference applied to this input. The voltage range for the external reference is from 1.2 V to VDD. Power Supply Input. The VDD range for the AD7888 is from 2.7 V to 5.25 V. Analog Ground. Ground reference point for all circuitry on the AD7888. All analog input signals and any external reference signals should be referred to this AGND voltage. Both of these pins should connect to the AGND plane of a system. Analog Input 1 through Analog Input 8. Eight single-ended analog input channels that are multiplexed into the on-chip track/hold. The analog input channel to be converted is selected by using the ADD0 through ADD2 bits of the Control Register. The input range for all input channels is 0 to VREF. Any unused input channels should be connected to AGND to avoid noise pickup. Data In. Logic Input. Data to be written to the AD7888's Control Register is provided on this input and is clocked into the register on the rising edge of SCLK (see Control Register section). Data Out. Logic Output. The conversion result from the AD7888 is provided on this output as a serial data stream. The bits are clocked out on the falling edge of the SCLK input. The data stream consists of four leading zeros followed by the 12 bits of conversion data, which is provided MSB first. Serial Clock. Logic Input. SCLK provides the serial clock for accessing data from the part and writing serial data to the Control Register. This clock input is also used as the clock source for the AD7888's conversion process. 3 4, 13 VDD AGND 5-12 AIN1-AIN8 14 15 DIN DOUT 16 SCLK REV. B -5- AD7888 TERMINOLOGY Integral Nonlinearity Peak Harmonic or Spurious Noise This is the maximum deviation from a straight line passing through the endpoints of the ADC transfer function. The endpoints of the transfer function are zero scale, a point 1/2 LSB below the first code transition, and full scale, a point 1/2 LSB above the last code transition. Differential Nonlinearity Peak harmonic or spurious noise is defined as the ratio of the rms value of the next largest component in the ADC output spectrum (up to fS/2 and excluding dc) to the rms value of the fundamental. Normally, the value of this specification is determined by the largest harmonic in the spectrum, but for ADCs where the harmonics are buried in the noise floor, it will be a noise peak. Intermodulation Distortion This is the difference between the measured and the ideal 1 LSB change between any two adjacent codes in the ADC. Offset Error This is the deviation of the first code transition (00 . . . 000) to (00 . . . 001) from the ideal, i.e., AGND + 0.5 LSB. Offset Error Match This is the difference in offset error between any two channels. Gain Error With inputs consisting of sine waves at two frequencies, fa and fb, any active device with nonlinearities will create distortion products at sum and difference frequencies of mfa nfb where m, n = 0, 1, 2, 3, etc. Intermodulation distortion terms are those for which neither m nor n is equal to zero. For example, the second order terms include (fa + fb) and (fa - fb), while the third order terms include (2fa + fb), (2fa - fb), (fa + 2fb) and (fa - 2fb). The AD7888 is tested using the CCIF standard where two input frequencies near the top end of the input bandwidth are used. In this case, the second order terms are usually distanced in frequency from the original sine waves while the third order terms are usually at a frequency close to the input frequencies. As a result, the second and third order terms are specified separately. The calculation of the intermodulation distortion is as per the THD specification where it is the ratio of the rms sum of the individual distortion products to the rms amplitude of the sum of the fundamentals expressed in dBs. Channel-to-Channel Isolation This is the deviation of the last code transition (111 . . . 110) to (111 . . . 111) from the ideal (i.e., VREF - 1.5 LSB) after the offset error has been adjusted out. Gain Error Match This is the difference in gain error between any two channels. Track/Hold Acquisition Time The track/hold amplifier returns into track mode at the end of conversion. Track/Hold acquisition time is the time required for the output of the track/hold amplifier to reach its final value, within 1/2 LSB, after the end of conversion. Signal to (Noise + Distortion) Ratio This is the measured ratio of signal to (noise + distortion) at the output of the A/D converter. The signal is the rms amplitude of the fundamental. Noise is the sum of all nonfundamental signals up to half the sampling frequency (fS/2), excluding dc. The ratio is dependent on the number of quantization levels in the digitization process; the more levels, the smaller the quantization noise. The theoretical signal to (noise + distortion) ratio for an ideal N-bit converter with a sine wave input is given by: Signal to (Noise + Distortion) = (6.02 N + 1.76) dB Thus for a 12-bit converter, this is 74 dB. Total Harmonic Distortion Channel-to-channel isolation is a measure of the level of crosstalk between channels. It is measured by applying a full-scale 25 kHz sine wave signal to all nonselected input channels and determining how much that signal is attenuated in the selected channel. The figure given is the worst case across all four or eight channels for the AD7888. PSR (Power Supply Rejection) Variations in power supply will affect the full-scale transition, but not the converter's linearity. Power supply rejection is the maximum change in the full-scale transition point due to a change in power-supply voltage from the nominal value. Total harmonic distortion (THD) is the ratio of the rms sum of harmonics to the fundamental. For the AD7888, it is defined as: THD (dB) = log 2 2 2 V22 + V3 + V42 + V5 + V6 V1 where V1 is the rms amplitude of the fundamental and V2, V3, V4 , V5 and V6 are the rms amplitudes of the second through the sixth harmonics. -6- REV. B AD7888 CONTROL REGISTER The Control Register on the AD7888 is an 8-bit, write-only register. Data is loaded from the DIN pin of the AD7888 on the rising edge of SCLK. The data is transferred on the DIN line at the same time as the conversion result is read from the part. This requires 16 serial clocks for every data transfer. Only the information provided on the first 8 rising clock edges (after CS falling edge) is loaded to the Control Register. MSB denotes the first bit in the data stream. The bit functions are outlined in Table I. The default contents of the Control Register on power-up is all zeros. Table I. Control Register Bit Function Description MSB DONTC ZERO ADD2 ADD1 ADD0 REF PM1 PM0 Bit 7 6 5 4 3 2 Mnemonic DONTC ZERO ADD2 ADD1 ADD0 REF Comment Don't Care. The value written to this bit of the Control Register is a don't care, i.e., it doesn't matter if the bit is 0 or 1. A zero must be written to this bit to ensure correct operation of the AD7888. These three address bits are loaded at the end of the present conversion sequence and select which analog input channel is converted for the next conversion. The selected input channel is decoded as shown in Table II. Reference Bit. With a 0 in this bit, the on-chip reference is enabled. With a 1 in this bit, the on-chip reference is disabled. To obtain best performance from the AD7888, the internal reference should be disabled when using an externally applied reference source. (See On-Chip Reference section.) Power Management Bits. These two bits decode the mode of operation of the AD7888 as shown in Table III. 1, 0 PM1, PM0 PERFORMANCE CURVES Figure 2 shows a typical FFT plot for the AD7888 at 100 kHz sample rate and 10 kHz input frequency. Figure 3 shows a typical plot for the SNR vs. frequency for a 5 V supply and with a 5 V external reference. 73.0 -10 -30 4096 POINT FFT SAMPLING 100kSPS fIN = 10kHz SNR = 70dB VDD = 5V 5V EXT REFERENCE 72.5 dB -50 SNR - dB 0 12.21 24.41 FREQUENCY - kHz 36.62 48.83 72.0 -70 71.5 -90 -110 71.0 0 10.89 21.14 INPUT FREQUENCY - kHz 31.59 42.14 Figure 2. Dynamic Performance Figure 3. SNR vs. Input Frequency REV. B -7- AD7888 Figure 4 shows the typical power supply rejection ratio vs. frequency for the part. The power supply rejection ratio is defined as the ratio of the power in the ADC output at frequency f to the power of a full-scale sine wave applied to the ADC of frequency fs: PSRR (dB) = 10 log (Pf/Pfs) Pf = Power at frequency f in ADC output, Pfs = power at frequency fs in ADC full scale input. Here a 100 mV peak-to-peak sine wave is coupled onto the VDD supply. Both the 2.7 V and 5.5 V supply performances are shown. -75 -77 -79 -81 PSRR - dB -83 -85 -87 -89 -91 -93 2.65 CHARGE REDISTRIBUTION DAC VDD = 5.5V/2.7V 100mV p-p SINE WAVE ON VDD REFIN = 2.488V EXT REFERENCE CHARGE REDISTRIBUTION DAC A AIN SW1 AGND B SAMPLING CAPACITOR CONTROL LOGIC ACQUISITION PHASE SW2 COMPARATOR (REF IN/REF OUT)/2 Figure 5. ADC Acquisition Phase When the ADC starts a conversion, (see Figure 6), SW2 will open and SW1 will move to Position B causing the comparator to become unbalanced. The control logic and the charge redistribution DAC are used to add and subtract fixed amounts of charge from the sampling capacitor to bring the comparator back into a balanced condition. When the comparator is rebalanced, the conversion is complete. The control logic generates the ADC output code. Figure 7 shows the ADC transfer function. A VIN SW1 12.85 23.15 33.65 43.85 INPUT FREQUENCY - kHz 54.35 64.15 SAMPLING CAPACITOR B CONTROL LOGIC CONVERSION PHASE SW2 COMPARATOR AGND Figure 4. PSRR vs. Frequency CIRCUIT INFORMATION (REF IN/REF OUT)/2 Figure 6. ADC Conversion Phase ADC TRANSFER FUNCTION The AD7888 is a fast, low power, 12-bit, single supply, 8-channel A/D converter. The part can be operated from 3 V (2.7 V to 3.6 V) supply or from 5 V (4.75 V to 5.25 V) supply. When operated from either a 5 V supply or a 3 V supply, the AD7888 is capable of throughput rates of 125 kSPS when provided with a 2 MHz clock. The AD7888 provides the user with an 8-channel multiplexer, on-chip track/hold, A/D converter, reference and serial interface housed in a tiny 16-lead TSSOP package, which offers the user considerable space saving advantages over alternative solutions. The serial clock input accesses data from the part and also provides the clock source for the successive-approximation A/D converter. The analog input range is 0 to VREF (where the externally-applied VREF can be between 1.2 V and VDD). The 8-channel multiplexer is controlled by the part's Control Register. This Control Register also allows the user to power-off the internal reference and to determine the Modes of Operation. CONVERTER OPERATION The output coding of the AD7888 is straight binary. The designed code transitions occur at successive integer LSB values (i.e., 1 LSB, 2 LSBs, etc.). The LSB size is = VREF/ 4096. The ideal transfer characteristic for the AD7888 is shown in Figure 7 below. 111...111 111...110 ADC CODE 111...000 1LSB = VREF/4096 011...111 000...010 000...001 000...000 0V 0.5LSB ANALOG INPUT +VREF - 1.5LSB The AD7888 is a successive-approximation analog-to-digital converter based around a charge redistribution DAC. Figures 5 and 6 show simplified schematics of the ADC. Figure 5 shows the ADC during its acquisition phase. SW2 is closed and SW1 is in Position A, the comparator is held in a balanced condition and the sampling capacitor acquires the signal on AIN. Figure 7. Transfer Characteristic -8- REV. B AD7888 TYPICAL CONNECTION DIAGRAM Figure 8 shows a typical connection diagram for the AD7888. Both AGND pins are connected to the analog ground plane of the system. VREF is connected to a well decoupled VDD pin to provide an analog input range of 0 V to VDD. The conversion result is output in a 16-bit word with four leading zeroes followed by the MSB of the 12-bit result. For applications where power consumption is of concern, the automatic power down at the end of conversion should be used to improve power performance. See Modes of Operation section of the data sheet. SUPPLY 2.7V TO 5.25V 10 F 0.1 F SERIAL INTERFACE VDD REF IN/ REF OUT For ac applications, removing high frequency components from the analog input signal is recommended by use of an RC lowpass filter on the relevant analog input pin. In applications where harmonic distortion and signal to noise ratio are critical the analog input should be driven from a low impedance source. Large source impedances will significantly affect the ac performance of the ADC. This may necessitate the use of an input buffer amplifier. The choice of the op amp will be a function of the particular application. When no amplifier is used to drive the analog input the source impedance should be limited to low values. The maximum source impedance will depend on the amount of total harmonic distortion (THD) that can be tolerated. The THD will increase as the source impedance increases and performance will degrade. Figure 10 shows a graph of the total harmonic distortion versus analog input signal frequency for different source impedances. -65 THD vs. FREQUENCY FOR DIFFERENT SOURCE IMPEDANCES -70 VDD = 5V 5V EXT REFERENCE RIN = 1k , CIN = 100pF THD - dB AD7888 0V TO REF IN/ REF OUT INPUT AIN1 AIN2 AIN8 AGND AGND SCLK DOUT C/ P DIN CS -75 RIN = 50 , CIN = 2.2nF -80 Figure 8. Typical Connection Diagram Analog Input Figure 9 shows an equivalent circuit of the analog input structure of the AD7888. The two diodes D1 and D2 provide ESD protection for the analog inputs. Care must be taken to ensure that the analog input signal never exceeds the supply rails by more than 200 mV. This will cause these diodes to become forwardbiased and start conducting current into the substrate. 20 mA is the maximum current these diodes can conduct without causing irreversible damage to the part. However, it is worth noting that a small amount of current (1 mA) being conducted into the substrate due to an overvoltage on an unselected channel, can cause inaccurate conversions on a selected channel. The capacitor C1 in Figure 9 is typically about 4 pF and can primarily be attributed to pin capacitance. The resistor R1 is a lumped component made up of the on resistance of a multiplexer and a switch. This resistor is typically about 100 . The capacitor C2 is the ADC sampling capacitor and has a capacitance of 20 pF typically. Note: The analog input capacitance seen when the track and hold is in track mode is typically 38 pF, while in hold mode it is typically 4 pF. VDD -85 RIN = 10 , CIN = 10nF -90 0.15 10.89 21.14 31.59 INPUT FREQUENCY - kHz 42.14 49.86 Figure 10. THD vs. Analog Input Frequency Analog Input Selection On power-up, the default AIN selection is AIN1. When returning to normal operation from power-down, the AIN selected will be the same one that was selected prior to power-down being initiated. Table II below shows the multiplexer address corresponding to each analog input from AIN1 to AIN8 for the AD7888. Table II. Channel Configurations ADD2 0 0 0 0 1 1 1 1 ADD1 0 0 1 1 0 0 1 1 ADD0 0 1 0 1 0 1 0 1 Analog Input Channel AIN1 AIN2 AIN3 AIN4 AIN5 AIN6 AIN7 AIN8 D1 R1 VIN C1 4pF D2 C2 20pF CONVERSION PHASE - SWITCH OPEN TRACK PHASE - SWITCH CLOSED On-Chip Reference Figure 9. Equivalent Analog Input Circuit The AD7888 has an on-chip 2.5 V reference. This reference can be enabled or disabled by clearing or setting the REF bit in the Control Register, respectively. If the on-chip reference is to be used externally in a system, it must be buffered before it is applied elsewhere. If an external reference is applied to the device, the internal reference is automatically overdriven. However, in REV. B -9- AD7888 order to obtain optimum performance from the device it is advised to disable the internal reference by setting the REF bit in the Control Register when an external reference is applied. When the internal reference is disabled, SW1 in Figure 11 will open and the input impedance seen at the REF IN/REF OUT pin is the input impedance of the reference buffer, which is in the region of giga . When the reference is enabled, the input impedance seen at the pin is typically 5 k. REF IN/REF OUT SW1 5k 2.5V the only way to fully power it up again is to reprogram the power management bits to PM1 = PM0 = 0, i.e., normal mode. In this case the device will power up on the 16th SCLK rising edge after the CS falling edge as this is when the power management bits become effective. Power-Up Times The AD7888 has an approximate 1 s power-up time when powering up from standby or when using an external reference. When VDD is first connected, the AD7888 will fully power up, i.e., it powers up in normal mode. If the part is put into shutdown, a subsequent power-up will take approximately 5 s. The AD7888 wake-up time is very short in the autostandby mode so it is possible to wake up the part and carry out a valid conversion in the same read/write operation. POWER vs. THROUGHPUT RATE Figure 11. On-Chip Reference Circuitry Table III. Power Management Options PM1 0 PM0 0 Mode Normal Operation. In this mode, the AD7888 remains in full power mode regardless of the status of any of the logic inputs. This mode allows the fastest possible throughput rate from the AD7888. Full Shutdown. In this mode, the AD7888 is in full shutdown mode with all circuitry on the AD7888, including the on-chip reference, entering its power-down mode. The AD7888 retains the information in the control Register bits while in full shutdown. The part remains in full shutdown until these bits are changed. Autoshutdown. In this mode, the AD7888 automatically enters full shutdown mode at the end of each conversion. Wake-up time from full shutdown is 5 s and the user should ensure that 5 s have elapsed before attempting to perform a valid conversion on the part in this mode. Autostandby. In this standby mode, portions of the AD7888 are powered down but the onchip reference voltage remains powered up. The REF bit should be 0 to ensure the on-chip reference is enabled. This mode is similar to autoshutdown but allows the part to power-up much faster. By operating the AD7888 in autoshutdown or autostandby mode the average power consumption of the AD7888 decreases at lower throughput rates. Figure 12 shows how as the throughput rate is reduced, the device remains in its power-down state longer and the average power consumption over time drops accordingly. For example, if the AD7888 were operated in a continuous sampling mode, with a throughput rate of 10 kSPS and a SCLK of 2 MHz (VDD = 5 V), and if PM1 = 1 and PM0 = 0, i.e., the device is in autoshutdown mode and the on-chip reference is used, the power consumption is calculated as follows. The power dissipation during normal operation is 3.5 mW (VDD = 5 V). If the power-up time is 5 s and the remaining conversionplus-acquisition time is 15.5 tSCLK, i.e., approximately 7.75 s, (see Figure 14a), the AD7888 can be said to dissipate 3.5 mW for 12.75 s during each conversion cycle. If the throughput rate is 10 kSPS, the cycle time is 100 s and the average power dissipated during each cycle is (12.75/100) x (3.5 mW) = 446.25 W. If VDD = 3 V SCLK = 2 MHz, and the device is again in autoshutdown mode using the on-chip reference, the power dissipation during normal operation is 2.1 mW. The AD7888 can now be said to dissipate 2.1 mW for 12.75 s during each conversion cycle. With a throughput rate of 10 kSPS, the average power dissipated during each cycle is (12.75/100) x (2.1 mW) = 267.75 W. Figure 12 shows the power vs. throughput rate for automatic shutdown with both 5 V and 3 V supplies. 10 0 1 1 0 1 1 The AD7888 provides flexible power management to allow the user to achieve the best power performance for a given throughput rate. The power management options are selected by programming the power management bits (i.e., PM1 and PM0) in the control register. Table III summarizes the options available. When the power management bits are programmed for either of the auto power-down modes, the part will enter the power-down mode on the 16th rising SCLK edge after the falling edge of CS. The first falling SCLK edge after the CS falling edge will cause the part to power up again. When the AD7888 is in full shutdown, POWER - mW POWER-DOWN OPTIONS 1 VDD = 5V SCLK = 2MHz VDD = 3V SCLK = 2MHz 0.1 0.01 0 10 20 30 THROUGHPUT - kSPS 40 50 Figure 12. Power vs. Throughput -10- REV. B AD7888 CS 1 SCLK THE PART REMAINS POWERED UP AT ALL TIMES AS PM1 AND PM0 = 0 16 DOUT 4 LEADING ZEROES + CONVERSION RESULT DIN DATA IN CONTROL REGISTER DATA IS LOADED ON THE FIRST 8 CLOCKS. PM1 AND PM0 = 0 TO KEEP THE PART IN THIS MODE Figure 13. Normal-Mode Operation MODES OF OPERATION Full Shutdown (PM1 = 0, PM0 = 1) The AD7888 has a number of different modes of operation. These are designed to provide flexible power management options. These options can be chosen to optimize the power dissipation/throughput rate ratio for differing application requirements. The modes of operation are controlled by the PM1 and PM0 bits of the Control Register as outlined previously. Normal Mode (PM1 = 0, PM0 = 0) This mode is intended for fastest throughput rate performance as the user does not have to worry about any power-up times with the AD7888 remaining fully powered all the time. Figure 13 shows the general diagram of the operation of the AD7888 in this mode. The data presented to the AD7888 on the DIN line during the first eight clock cycles of the data transfer are loaded to the Control Register. The part will remain powered up at the end of the conversion as long as PM1 and PM0 were set to zero in the write during that conversion. To continue to operate in this mode, the user must ensure that PM1 and PM0 are both loaded with 0 on every data transfer. The falling edge of CS initiates the sequence and the input signal is sampled on the second rising edge of the SCLK input. Sixteen serial clock cycles are required to complete the conversion and access the conversion result. Once a data transfer is complete (CS has returned high), another conversion can be initiated immediately by bringing CS low again. THE PART ENTERS SHUTDOWN AT THE END OF CONVERSION AS PM1 = 1 AND PM0 = 0 In this mode, all internal circuitry on the AD7888, including the on-chip reference, is powered-down. The part retains the information in the Control Register during full shutdown. The part remains in full shutdown until the power management bits are changed. If the power management bits are changed to PM1 = 1 and PM0 = 0, i.e., the autoshutdown mode, the part will remain in shutdown (now in autoshutdown) but will power up once a conversion is initiated after that (see Power-Up Times section). The part changes mode as soon as the control register has been updated, so if the part is in full shutdown mode and the power management bits are changed to PM1 = PM0 = 0, i.e., normal mode, then the part will power up on the 16th SCLK rising edge. Autoshutdown (PM1 = 1, PM0 = 0) In this mode, the AD7888 automatically enters its power-down mode at the end of every conversion. Figure 14a shows the general diagram of the operation of the AD7888 in this mode. When CS goes from high to low, all on-chip circuitry will start to power up on the next falling edge of SCLK. On the sixteenth SCLK rising edge the part will power down again. It takes approximately 5 s for the AD7888 internal circuitry to be fully powered up. As a result, a conversion (or sample-and-hold acquisition) should not be initiated during this 5 s. The input signal is sampled on the second rising edge of SCLK following the CS falling edge. The user should ensure that 5 s elapse between the first falling edge of SCLK after the falling edge of THE PART POWERS UP FROM SHUTDOWN ON SCLK FALLING EDGE AS PM1 = 1 AND PM0 = 0 CS 1 SCLK 16 1 2 16 t10 = 5 s DOUT 4 LEADING ZEROES + CONVERSION RESULT 4 LEADING ZEROES + CONVERSION RESULT DIN DATA IN DATA IN CONTROL REGISTER DATA IS LOADED ON THE FIRST 8 CLOCKS. PM1 = 1 AND PM0 = 0 PM1 = 1 AND PM0 = 0 TO KEEP THE PART IN THIS MODE Figure 14a. Autoshutdown Operation REV. B -11- AD7888 THE PART ENTERS SHUTDOWN AT THE END OF CONVERSION AS PM1 = 1 AND PM0 = 0 CS 1 SCLK 8 16 1 8 16 1 8 16 THE PART BEGINS TO POWERUP FROM SHUTDOWN THE PART REMAINS POWERED UP AS PM1 AND PM0 = 0 THE PART ENTERS SHUTDOWN AT THE END OF CONVERSION AS PM1 = 1 AND PM0 = 0 DOUT 4 LEADING ZEROES + CONVERSION RESULT 4 LEADING ZEROES + CONVERSION RESULT 4 LEADING ZEROES + CONVERSION RESULT DIN DATA IN DATA IN DATA IN CONTROL REGISTER DATA IS LOADED ON THE FIRST 8 CLOCKS. PM1 = 1 AND PM0 = 0 PM1 AND PM0 = 0 TO PLACE THE PART IN NORMAL MODE PM1 = 1 AND PM0 = 0 TO PLACE THE PART BACK IN AUTOSHUTDOWN MODE Figure 14b. Autoshutdown Operation CS and the second rising edge of SCLK as shown in Figure 14a. In microcontroller applications, this is readily achievable by driving the CS input from one of the port lines and ensuring that the serial data read (from the microcontrollers serial port) is not initiated for 5 s. In DSP applications, where the CS is generally derived from the serial frame synchronization line, it is not possible to separate the first falling edge and second rising edge of SCLK after the CS falling edge by up to 5 s. Therefore, the user will need to write to the Control Register to exit this mode and (by writing PM1 = 0 and PM0 = 0) put the part into normal mode. A second conversion will then need to be initiated when the part is powered up to obtain a conversion result as shown in Figure 14b. Autostandby (PM1 = 1, PM0 = 1) In this mode, the AD7888 automatically enters a standby (or sleep) mode at the end of every conversion. In this standby mode, all on-chip circuitry, apart from the on-chip reference, is powered down. This mode is similar to the autoshutdown but in this case, the power-up time is much shorter as the on-chip reference remains powered up at all times. Figure 15 shows the general diagram of the operation of the AD7888 in this mode. On the first falling SCLK edge after CS goes low, the AD7888 comes out of standby. The AD7888 wake-up time is very short in this mode so it is possible to wake up the part and carry out a valid conversion in the same read/ write operation. The input signal is sampled on the second rising edge of SCLK following the CS falling edge. At the end of conversion (last rising edge of SCLK) the part automatically enters its standby mode. THE PART ENTERS STANDBY AT THE END OF CONVERSION AS PM1 = 1 AND PM0 = 1 CS 1 SCLK 16 THE PART POWERS UP FROM STANDBY ON SCLK FALLING EDGE AS PM1 = 1 AND PM0 = 1 1 16 DOUT 4 LEADING ZEROES + CONVERSION RESULT 4 LEADING ZEROES + CONVERSION RESULT DIN DATA IN DATA IN CONTROL REGISTER DATA IS LOADED ON THE FIRST 8 CLOCKS. PM1 = 1 AND PM0 = 1 PM1 = 1 AND PM0 = 1 TO KEEP THE PART IN THIS MODE Figure 15. Autostandby Operation -12- REV. B AD7888 SERIAL INTERFACE Figure 16 shows the detailed timing diagram for serial interfacing to the AD7888. The serial clock provides the conversion clock and also controls the transfer of information to and from the AD7888 during conversion. CS initiates the data transfer and conversion process. For the autoshutdown mode, the first falling edge of SCLK after the falling edge of CS wakes up the part. In all cases, it gates the serial clock to the AD7888 and puts the on-chip track/hold into track mode. The input signal is sampled on the second rising edge of the SCLK input after the falling edge of CS. Thus, the first one and one-half clock cycles after the falling edge of CS is when the acquisition of the input signal takes place. This time is denoted as the acquisition time (tACQ). In autoshutdown mode, the acquisition time must allow for the wake-up time of 5 s. The on-chip track/hold goes from track mode to hold mode on the second rising edge of SCLK and a conversion is also initiated on this edge. The conversion process takes a further fourteen and one-half SCLK cycles to complete. The rising edge of CS will put the bus back into three-state. If CS is left low a new conversion will be initiated. The input channel that is sampled is the one selected in the previous write to the Control Register. Thus, the user must write ahead of the channel for conversion. In other words, the user must write the channel address for the next conversion while the present conversion is in progress. Writing of information to the Control Register takes place on the first eight rising edges of SCLK in a data transfer. The Control Register is always written to when a data transfer takes place. The user must be careful to always set up the correct information on the DIN line when reading data from the part. Sixteen serial clock cycles are required to perform the conversion process and to access data from the AD7888. In applications where the first serial clock edge, following CS going low, is a falling edge, this edge clocks out the first leading zero. Thus, the first rising clock edge on the SCLK clock has the first leading zero provided. In applications where the first serial clock edge, following CS going low, is a rising edge, the first leading zero may not be set up in time for the processor to read it correctly. However, subsequent bits are clocked out on the falling edge of SCLK so they are provided to the processor on the following rising edge. Thus, the second leading zero is clocked out on the falling edge subsequent to the first rising edge. The final bit in the data transfer is valid on the 16th rising edge, having being clocked out on the previous falling edge. NOTE: The mark space ratio for SCLK is specified for at least 40% high time (with corresponding 60% low time) or 40% low time (with corresponding 60% high time). As the SCLK frequency is reduced, the mark space ratio may vary provided the conversion time never exceeds 50 s--to avoid capacitive droop effects. t ACQ CS t CONVERT t1 SCLK THREESTATE 1 2 t6 3 4 5 6 15 16 t2 t7 4 LEADING ZEROS t3 DB11 DB10 DB9 DB0 t8 DOUT THREESTATE t4 t5 DIN DONTC ZERO ADD2 ADD1 ADD0 REF PM1 PM0 Figure 16. Serial Interface Timing Diagram REV. B -13- AD7888 MICROPROCESSOR INTERFACING The serial interface on the AD7888 allows the part to be directly connected to a range of many different microprocessors. This section explains how to interface the AD7888 with some of the more common microcontroller and DSP serial interface protocols. AD7888 to TMS320C5x The serial interface on the TMS320C5x uses a continuous serial clock and frame synchronization signals to synchronize the data transfer operations with peripheral devices like the AD7888. The CS input allows easy interfacing with an inverter between the serial clock of the TMS320C5x and the AD7888 being the only glue logic required. The serial port of the TMS320C5x is set up to operate in burst mode with internal CLKX (TX serial clock) and FSX (TX frame sync). The serial port control register (SPC) must have the following setup: FO = 0, FSM = 1, MCM = 1 and TXM = 1. The connection diagram is shown in Figure 17. AD7888* SCLK The Timer Registers, etc., are loaded with a value that will provide an interrupt at the required sample interval. When an interrupt is received, a value is transmitted with TFS/DT (ADC control word). The TFS is used to control the RFS and hence the reading of data. The frequency of the serial clock is set in the SCLKDIV Register. When the instruction to transmit with TFS is given, (i.e., AX0 = TX0), the state of the SCLK is checked. The DSP will wait until the SCLK has gone high, low and high before transmission will start. If the timer and SCLK values are chosen such that the instruction to transmit occurs on or near the rising edge of SCLK, the data may be transmitted or it may wait until the next clock edge. For example, the ADSP-2111 has a master clock frequency of 16 MHz. If the SCLKDIV Register is loaded with the value 3, a SCLK of 2 MHz is obtained, and eight master clock periods will elapse for every one SCLK period. If the timer registers are loaded with the value 803, then 100.5 SCLKs will occur between interrupts and subsequently between transmit instructions. The situation will result in nonequidistant sampling as the transmit instruction is occurring on a SCLK edge. If the number of SCLKs between interrupts is not a figure of N.5, equidistant sampling will be implemented by the DSP. AD7888* SCLK DOUT TMS320C5x* CLKX CLKR DOUT DIN CS DR DT FSX FSR ADSP-21xx* SCLK DR DT RFS TFS *ADDITIONAL PINS OMITTED FOR CLARITY DIN Figure 17. Interfacing to the TMS320C5x AD7888 to ADSP-21xx CS The ADSP-21xx family of DSPs are interfaced to the AD7888 with an inverter between the serial clock of the ADSP-21xx and the AD7888. This is the only glue logic required. The SPORT control register should be set up as follows: TFSW = RFSW = 1, Alternate Framing INVRFS = INVTFS = 1, Active Low Frame Signal DTYPE = 00, Right Justify Data SLEN = 1111, 16-Bit Data Words ISCLK = 1, Internal Serial Clock TFSR = RFSR = 1, Frame Every Word IRFS = 0 ITFS = 1 The connection diagram is shown in Figure 18. The ADSP21xx has the TFS and RFS of the SPORT tied together with TFS set as an output and RFS set as in input. The DSP operated in Alternate Framing Mode and the SPORT Control Register is set up as described. The frame synchronization signal generated on the TFS is tied to CS and, as with all signal processing applications, equidistant sampling is necessary. However, in this example the timer interrupt is used to control the sampling rate of the ADC and, under certain conditions, equidistant sampling may not be achieved. *ADDITIONAL PINS OMITTED FOR CLARITY Figure 18. Interfacing to the ADSP-21xx AD7888 to DSP56xxx The connection diagram in Figure 19 shows how the AD7888 can be connected to the SSI (Synchronous Serial Interface) of the DSP56xxx family of DSPs from Motorola. The SSI is operated in synchronous mode (SYN bit in CRB = 1) with internally generated 1-bit clock period frame sync for both TX and RX (bits FSL1 = 1 and FSL0 = 0 in CRB). Set the word length to 16 by setting bits WL1 = 1 and WL0 = 0 in CRA. An inverter is also necessary between the SCLK from the DSP56xxx and the SCLK pin of the AD7888 as shown in Figure 19. AD7888* SCLK DOUT DIN CS DSP56xxx* SCK SRD STD SC2 *ADDITIONAL PINS OMITTED FOR CLARITY Figure 19. Interfacing to the DSP56xxx -14- REV. B AD7888 AD7888 to MC68HC11 The Serial Peripheral Interface (SPI) on the MC68HC11 is configured for Master Mode (MSTR = 1), Clock Polarity Bit (CPOL) = 1 and the Clock Phase Bit (CPHA) = 1. The SPI is configured by writing to the SPI Control Register (SPCR)--see 68HC11 User Manual. The serial transfer will take place as two 8-bit operations. A connection diagram is shown in Figure 20. AD7888* SCLK DOUT DIN CS APPLICATION HINTS Grounding and Layout The AD7888 has very good immunity to noise on the power supplies as can be seen by the PSRR vs. Frequency graph. However, care should still be taken with regard to grounding and layout. The printed circuit board that houses the AD7888 should be designed so the analog and digital sections are separated and confined to certain areas of the board. This facilitates the use of ground planes that can be easily separated. A minimum etch technique is generally best for ground planes as it gives the best shielding. Digital and analog ground planes should be joined in only one place. Both AGND pins of the AD7888 should be sunk in the AGND plane. The AGND plane and DGND plane connection should be made at one point only, a star ground point that should be established as close as possible to an AGND pin of the AD7888. Avoid running digital lines under the device as these will couple noise onto the die. The analog ground plane should be allowed to run under the AD7888 to avoid noise coupling. The power supply lines to the AD7888 should use as large a trace as possible to provide low impedance paths and reduce the effects of glitches on the power supply line. Fast switching signals like clocks should be shielded with digital ground to avoid radiating noise to other sections of the board, and clock signals should never be run near the analog inputs. Avoid crossover of digital and analog signals. Traces on opposite sides of the board should run at right angles to each other. This will reduce the effects of feedthrough through the board. A microstrip technique is by far the best but is not always possible with a double-sided board. In this technique, the component side of the board is dedicated to ground planes while signals are placed on the solder side. Good decoupling is also important. All analog supplies should be decoupled with 10 F tantalum in parallel with 0.1 F capacitors to AGND. To achieve the best from these decoupling components, they must be placed as close as possible to the device, ideally right up against the device. Evaluating the AD7888 Performance MC68HC11* SCLK/PD4 MISO/PD2 MOSI/PD3 PA0 *ADDITIONAL PINS OMITTED FOR CLARITY Figure 20. Interfacing to the MC68HC11 AD7888 to 8051 It is possible to implement a serial interface using the data ports on the 8051. This allows a full duplex serial transfer to be implemented. The technique involves "bit-banging" an I/O port (e.g., P1.0) to generate a serial clock and using two other I/O ports (e.g., P1.1 and P1.2) to shift data in and out--see Figure 21. AD7888* SCLK DOUT DIN CS P1.0 P1.1 P1.2 P1.3 8051* *ADDITIONAL PINS OMITTED FOR CLARITY Figure 21. Interfacing to the 8051 Using I/O Ports AD7888 to PIC16C6x/7x The PIC16C6x Synchronous Serial Port (SSP) is configured as an SPI Master with the Clock Polarity Bit = 1. This is done by writing to the Synchronous Serial Port Control Register (SSPCON). See user PIC16/17 Microcontroller User Manual. Figure 22 shows the hardware connections needed to interface to the PIC16/17. In this example I/O port RA1 is being used to pulse CS. This microcontroller only transfers eight bits of data during each serial transfer operation. Therefore, two consecutive read/write operations are needed. AD7888* SCLK DOUT DIN CS The recommended layout for the AD7888 is outlined in the evaluation board for the AD7888. The evaluation board package includes a fully assembled and tested evaluation board, documentation, and software for controlling the board from the PC via the EVAL-CONTROL BOARD. The EVAL-CONTROL BOARD can be used in conjunction with the AD7888 evaluation board, as well as many other Analog Devices evaluation boards ending in the CB designator, to demonstrate/evaluate the ac and dc performance of the AD7888. The software allows the user to perform ac (fast Fourier transform) and dc (histogram of codes) tests on the AD7888. PIC16C6x/7x* SCK/RC3 SDO/RC5 SDI/RC4 RA1 *ADDITIONAL PINS OMITTED FOR CLARITY Figure 22. Interfacing to the PIC16C6x/17x REV. B -15- AD7888 OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 16-Lead Small Outline (SOIC) (R-16A) C01356-0-6/01(B) 0.3937 (10.00) 0.3859 (9.80) 16 9 8 0.1574 (4.00) 0.1497 (3.80) 1 0.2440 (6.20) 0.2284 (5.80) PIN 1 0.0098 (0.25) 0.0040 (0.10) 0.0688 (1.75) 0.0532 (1.35) 0.0196 (0.50) x 45 0.0099 (0.25) 0.0500 SEATING (1.27) PLANE BSC 0.0192 (0.49) 0.0138 (0.35) 0.0099 (0.25) 0.0075 (0.19) 8 0 0.0500 (1.27) 0.0160 (0.41) 16-Lead Thin Shrink Small Outline (TSSOP) (RU-16) 0.201 (5.10) 0.193 (4.90) 16 9 0.177 (4.50) 0.169 (4.30) 1 8 PIN 1 0.006 (0.15) 0.002 (0.05) 0.0433 (1.10) MAX 0.0118 (0.30) 0.0075 (0.19) 0.256 (6.50) 0.246 (6.25) 0.0256 SEATING (0.65) PLANE BSC 8 0 0.0079 (0.20) 0.0035 (0.090) 0.028 (0.70) 0.020 (0.50) AD7888-Revision History Data Sheet changed from REV. A to REV. B. Edit to DC Accuracy section of Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 PRINTED IN U.S.A. Location Page -16- REV. B |
Price & Availability of EVAL-CONTROLBOARD
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