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- 1 - ? andigilog, inc. 2006 www.andigilog.com october 2006 - 70a05011 l ow - oltage 1-w ire d igital t emperature s ensor asc7521 a v p roduct s pecification product description the ASC7521A is a high-precision cmos temperature sensor and voltage monitor with simple serial transport (sst) compatible serial digital interface, intended for use in pc hardware monitor applications. communication of device capabilities and temperature readings takes place over the high-speed bi-directional sst interface. the sst temperature sensor provides a means for an analog signal to travel over a digital bus enabling remote temperature sensing in areas previously not monitored in the pc. the temperature sensor supports an internal and external thermal diode. sensor localization is aided by two address pins that distinguish multiple sensors on the same bus. the ASC7521A is available in msop-8 surface mount package. features ? on-chip and remote temperature sensors ? accuracy: o +/- 3c over operational range o internal +/- 2c over 40c to 70c o remote +/- 1c over 50c to 70c ? operational range: -40c to 125c ? temperature resolution: 0.125c ? 1-wire sst serial interface ? negotiable sst signaling rate up to 2-mbps ? temperature and errors reported over sst ? internally corrected for diode non-ideality and series resistance ? 3-state address pins set one of 9 sst bus address 0x48 through 0x50 ? 8-lead msop package ? msl-1 per jedec j-std-020c ? pb-free matte sn leadfinish & rohs compliant packages pin configuration v dd 8 sst 1 7 gnd a dd0 2 3 d+ gnd 6 applications desktop and notebook computers application diagram ordering information part number package temp. range and operating voltage marking supplied in ASC7521Am8 8-lead msop -40c to 125c, 3.3v 521a ayww 2500 units tape & reel ayww ? assembly site, year, workweek 4 d- ASC7521A add1 cpu 3.3v ASC7521A sst interface sst add0 1 3 4 5 add1 5 7 8 2, 6
- 2 - ? andigilog, inc. 2006 www.andigilog.com october 2006 - 70a05011 ASC7521A absolute maxi mum ratings 1 parameter rating supply voltage, v dd -0.3, +3.63v voltage on any digital input or output 3 -0.3v to v dd + 0.3v input current on any pin 3 5ma package input current 3 20ma relative humidity (non-operating) 5% - 85% rh @ 25 c to 70 c maximum junction temperature, tjmax 150 c storage temperature range -60 c to +150 c ir reflow peak temperature 260 c lead soldering temperature (10 sec.) 300 c human body model 2000 v machine model 250 v esd 5 charged-device model >1000 v notes: 1. absolute maximum ratings are limits beyond which operation may cause permanent damage to the device. these are stress ratings only; functional operation at or above these limits is not implied. for guaranteed specifications and test conditions, see the el ectrical characteristics. the guaranteed specifications apply only for the test conditions listed. some performance characteristics may degrade when the device is not operated under the listed test conditions. 2. all voltages are measured with respect to gnd, unless otherwise specified. 3. when the input voltage (vin) at any pin exceeds the power supplies (vin< (gnd or gnda) or vin>v+, except for sst and analog voltage inputs), the current at that pin should be limited to 5ma. the 20ma maximum package input current rating limits to number of pins that can safely exceed the power supplies with an input current of 5ma to four. 4. the maximum power dissipation must be de-rated at elevated temperatures and is dictated by tjmax, ja and the ambient temperature, t a . the maximum allowable power dissipation at any temperature is pd = (tjmax - ta) / ja . it must also take into account self-heating that can adversely affect the accuracy of internal sensors. 5. human body model: 100pf capacitor discharged through a 1.5k resistor into each pin. machine model: 200pf capacitor discharged directly into each pin. charged-device model is per jesd22-c101c. electrical characteristics 6 (- 40c t +125c, v = 3 . 3 v unless otherwise noted. specifications subject to change without notice) a dd parameter conditions min typ max units supply voltage v dd 3.0 3.3 3.6 v sst signal meets sst specification version 1.0 for 1.5v interface - 40c t a +125c 3 c local sensor accuracy 7, 8 40c t a 70c 2 c local sensor resolution 0.125 c 0c t a 70c, -40c t d +125c 3 c remote diode sensor accuracy 7, 8, 9 0c t a 70c, 50c t d 70c 1 c remote diode sensor resolution 0.125 c temperature monitor cycle time 10 t c 0.2 sec notes: 6. these specifications are guarante ed only for the test conditions listed. 7. accuracy (expressed in c) = difference between the ASC7521A reported temperature and the device temperature. 8. the ASC7521A can be read at any time without interrupting the temperature conversion process. 9. calibration of the remote diode sensor input is set to meet the accuracy limits with a cpu thermal diode that has a non-ide ality factor of 1.009 with a series resistance of 4.52 ? . 10. total monitoring cycle time for all temperature and analog input voltage measurements is 0.2 second.
- 3 - ? andigilog, inc. 2006 www.andigilog.com october 2006 - 70a05011 ASC7521A pin descriptions pin # name direction description 1 v dd (3.3v) supply supply voltage, 3.3v +/- 10% 2 gnd supply ground 3 d+ current source remote diode anode or positive lead 4 d- current sink remote diode cathode or negative lead 5 add1 input device address tri-state selector: ground, float or v dd select device address 6 gnd supply ground 7 add0 input device address tri-state selector: ground, float or v dd select device address 8 sst input digital input / outpu t. sst bi-directional data line. figure 1. block diagram on- chip sensor control and sst interface adc remote diode open / short add1 add0 sst d + d - on - chip t emp erature remote temp erature dib register vdd vss
- 4 - ? andigilog, inc. 2006 www.andigilog.com october 2006 - 70a05011 ASC7521A sst sensors the sst temperature sensor provides a means for an analog signal to travel over a single-wire digital bus enabling remote temperature sensing in areas previously not monitored in the pc. the temperature sensor supports an internal temperature sensor and external thermal diodes. this section outlines general requirements for simple serial transport (sst) sensors intended for use in pc desktop applications that conform to sst version 1.0 specification. the ASC7521A reports external temperature sensed by a remote diode-connected transistor and an internal temperature measurement. addressing the ASC7521A complies with the address range set aside for fixed-address, discoverable devices as defined in the sst specification version 1.0. si mple temperature sensors use fixed addresses in the range of 0x48 to 0x50. the ASC7521A may be programmed to any of these addresses via the address select pins ad0 and ad1. frame check sequence (fcs) each message requires a frame check sequence byte to ensure reliable data exchange between host and client. the message originator and client both make an fcs calculation. one fcs byte must be returned from the message target to the originator after all bytes including the header and the data block are written. if data is read from the target, a second fcs byte must follow the data block read. the fcs byte is the result of an 8-bit cyclic redundancy check (crc) of the each data block preceding the fcs up to the most recent, earlier fcs byte. the first fcs in the message does not include the two address timing negotiation ?0? bits that precede the address byte or the message timing negotiation bit after the address byte. the first fcs does include the address byte in its computation. the fcs is initialized at 0x00 and is calculated in a way that confor ms to a crc-8 represented by the crc polynomial, c(x) = x 8 + x 2 + x + 1. bus voltage all sst sensor devices used for pc applications must be capable of operating the sst inte rface portion of the sensor device at 1.5 volts as defined in 1.5 volt static (dc) characteristics section of the sst version 1.0 specification . bus timing all sst sensor devices must be able to negotiate timing and operate at a maximum bus transfer rate of 2-mbps. if the bus address timing is negotiated at a lower rate due to the performance limitations of other devices on the bus, the sensor device will operate at that lower rate. device power-on timing following a power-on reset, such as a system transitioning from s3-s5 to s0, the ASC7521A will be able to participate in the address and message timing negotiation and respond to required sst bus commands such as respond to a getdib() command within 10ms of the device?s v dd rail reaching 90%. the ASC7521A has an internal power on reset and will be fully functional within 50ms of power on. the ASC7521A does not employ any device power management. voltage and temperature sensor data little endian format the bit level transfer is defined in the sst specification. the 2- byte data values are returned in little endian format, in other words, the lsb is sent first followed by msb. for multi-function devices that allow access to multiple sensors, the data is returned lsb followed by the msb for the first sensor, lsb followed by the msb for the second sensor, and so on. the specific order is explicitly specified in the command description. atomic readings the ASC7521A ensures that every value returned is derived from a single analog to digital conversion and is not skewed (e.g. the msb and the lsb come from two different conversions). conversion time the maximum refresh time for all temperature values is 200ms. the ASC7521A provides the logic to ensure all readings meet the conversion time requirements. temperature data data precision, accuracy and resolution the temperature data meet s the following minimum requirements: ? operational range: -40c to +125c ? internal sensor accuracy: o +/- 3c over operational range o +/- 2c over 40c to 70c ? remote sensor accuracy (when ta is from 0c to 70c): o +/- 3c over operational range o +/- 1c over 50c to 70c ? resolution: 0.125c temperature data format the data format is capable of reporting temperature values in the range of +/-512c. the temperature sensor data is returned as a 2?s complement 16-bit binary value. it represents the number of 1/64c increments in the actual reading. this allows temperatures to be repr esented with approximately a 0.016c resolution.
- 5 - ? andigilog, inc. 2006 www.andigilog.com october 2006 - 70a05011 ASC7521A values that would represent temperatures below -273.15c (0 k or absolute zero) are reserved and are not be returned except as specifically noted. for the ASC7521A the required resolution is 0.125c. bits [2:0] will be defined but they are beyond the required resolution. the sign bit will indicate a negative temperature except when reporting an error condition (see sensor error condition ). temperature 2?s complement representation 80c 0001 0100 0000 0000 79.875c 0001 0011 1111 1000 1c 0000 0000 0100 0000 0c 0000 0000 0000 0000 -1c 1111 1111 1100 0000 -5c 1111 1110 1100 0000 table 1. temperature representation sign integer temperature 0c to 512c fractional temperature lsb 0.125c always zero 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 figure 2. temperature reading a to d converter resolution and mapping the mapping of the a-d converter bit values is a two?s complement representation with the binary point between bits 5 and 6 of the 16-bit data word. bit 15 is the sign, bits 14 through 6 are integer temperature in degrees, bits 5 down to 3 are the fractional part with 0.125c as the lsb. the lowest 3 bits are set to zero. temperature inputs the simple temperature sensor has an internal thermal sensor plus an external sensor using a remote diode. both temperature readings are internally corrected for lead resistance and non-ideality for the thermal diode of a pentium? 4, 65nm process (1.009 non-ideality, 4.35 ? lead resistance). the range of measurement currents falls within the intel recommended range of 10 a and 170 a to minimize the impact of beta variation in the cpu substrate thermal diode. note that pent ium 4, 90 nm process is 1.011 non-ideality and series resistance of 3.33 ?. if a diode connected discrete transistor is used instead of a cpu diode, a correction must be applied to the reading to compensate for the difference in non-ideality. a 2n3904 npn transistor has a non-ideality ( ) factor of approximately 1.04. to correct the value reported to the actual temperature use the following formula: t actual = t reported x transistor / 1.009 it is recommended that the actual transistor type and manufacturers chosen for the remote sensor be characterized for non-ideality as part of system qualification. sensor error condition the ASC7521A has the capability to detect and report open or shorted external diode inputs per sensor error condition. when an error or failure condition is detected, the sensor device must return a large negative value in response to either the getinttemp() or ge texttemp() command. in this manner software is provided with a means to determine whether or not the sensor is working normally and that the data returned is good. the ASC7521A will write one of the values from the table below to appropriate memory locations for getinttemp() and/or getexttemp(). the ASC7521A uses the oem defined values of 0x8102 (open) and 0x8103 (short) rat her than the generic errors defined for codes 0x8000 to 0x8003. error code description 0x8000 to 0x80ff reserved 0x8102 remote diode open 0x8103 remote diode short 0x8100-0x81ff reserved table 2. error codes
- 6 - ? andigilog, inc. 2006 www.andigilog.com october 2006 - 70a05011 ASC7521A sst interface multi client mode sensors operate in multi-client mode for read bit timing. reference the sst specificat ion version 1.0 for details. sst device commands getdib() command (0xf7) read the device identifier block (dib). the read length of the command is either 8 or 16 bytes. 8 bytes is the minimum numbe r of bytes populated by a fixed address discoverable client. write data length: 0x01 read data length: 0x08/0x10 command code: 0xf7 note: un-shaded table entries are created by the host. shaded entries are the response bytes from the ASC7521A to the host. # bits # bits host sending ASC7521A sending hex value hex value 8 8 8 8 8 target address write length read length getdib cmd fcs 0x48 0x01 0x10 0xf7 0xdc 8 8 8 8 8 dib byte 1 ? dib byte 15 dib byte 16 fcs (data) (data) (data) (data) (data dependent) figure 3. getdib() command (16-byte read length) 8 8 8 8 8 target address write length read length getdib cmd fcs 0x48 0x01 0x08 0xf7 0x23 8 8 8 8 8 dib byte 1 ? dib byte 7 dib byte 8 fcs (data) (data) (data) (data) (data dependent) figure 4. getdib() command (8-byte read length) ping() command the ping() command provides a safe means for software to ve rify that a device is responding at a particular address. write data length: 0x00 read data length: 0x00 command code: none 8 8 8 8 target address write length read length fcs 0x48 0x00 0x00 0xd7 figure 5. example of ping()
- 7 - ? andigilog, inc. 2006 www.andigilog.com october 2006 - 70a05011 ASC7521A resetdevice() command the resetdevice() command is used to reset all device functions to their power-on reset values. it is used by the system to re cover from serious hardware or bus errors. write data length: 0x01 read data length: 0x00 command code: 0xf6 8 8 8 8 8 target address write length read length resetdevice command fcs 0x48 0x01 0x00 0xf6 0x8c figure 6. resetdevice() format targeting a non-default address 8 8 8 8 target address write length read length resetdevice command 0x00 0x01 0x00 0xf6 figure 7. resetdevice() format targeting the default address sensor command summary getinttemp() returns the temperature of the dev ice?s internal thermal sensor. write data length: 0x01 read data length: 0x02 command code: 0x00 example bus transaction for a thermal sensor device lo cated at address 0x48 returning a value of 60c: 8 8 8 8 target address write length read length command 0x48 0x01 0x02 0x00 8 8 8 8 fcs lsb msb fcs 0x6a 0x00 0x0f 0x2d figure 8. get internal temperature command example getexttemp() returns the temperature of the external thermal diode. write data length: 0x01 read data length: 0x02 command code: 0x01 getalltemps() returns a 4-byte block of data containing both the internal and ex ternal temperatures in the foll owing order internal then exte rnal temperatures.
- 8 - ? andigilog, inc. 2006 www.andigilog.com october 2006 - 70a05011 ASC7521A write data length: 0x01 read data length: 0x04 command code: 0x00 optional sst device commands the optional sst commands alert() , suspend() are not supported in the ASC7521A. vendor specific extensions the vendor specific command codes are in t he range from 0xe0 and 0xe7. reading and writing to specific internal registers is provided for custom tuning of sens or response characteristics. writereg () writes to the sensor?s internal registers. write data length: 2+n (command + address + number of bytes to write) read data length: 0x00 command code: 0xe0 example bus transaction to write to a sensor located at address 0x48. this example writes 2 c onsecutive locations (0x20 and 0x 21) to values 0x25 and 0x28. 8 8 8 8 target address write length read length command 0x48 0x04 0x00 0xe0 8 8 8 8 ram addr write data write data fcs 0x20 0x25 0x28 0x1b figure 9. example register write readreg () reads from the sensor?s internal registers. write data length: 0x02 (command + address) read data length: n (number of bytes to read) command code: 0xe1 example bus transaction to read a sensor lo cated at address 0x48. this example r eads 2 consecutive locations (0x20 and 0x21). 8 8 8 8 target address write length read length command 0x48 0x02 0x02 0xe1 8 8 8 8 ram addr fcs read data read data fcs 0x20 0x9d 0x25 0x28 0x37 figure 10. example register read vencmdenable () vendor command enable enables t he vendor specified extensions. write data length: 0x01 read data length: 0x00 command code: 0xe2
- 9 - ? andigilog, inc. 2006 www.andigilog.com october 2006 - 70a05011 ASC7521A 8 8 8 8 8 target address write length read length command fcs 0x48 0x01 0x00 0xe2 0xe0 figure 11. vendor command enable vencmddisable () vendor command disable disables the vendor specified extensions. write data length: 0x01 read data length: 0x00 command code: 0xe3 8 8 8 8 8 target address write length read length command fcs 0x48 0x01 0x00 0xe3 0xe7 figure 12. vendor command disable reserved or unsupported commands attempts to access the sensor using a reserved or unsupported co mmand will not result in the device or bus failure. the sensor will return a modified fcs when any of the following commands are receiv ed. to modify the fcs the sensor will invert all of the bit s in the correct fcs (1?s complement). a modified fcs is also called an abort fcs. the sensor will return an abort fcs (modified fcs) for a reserved and unsupported command code (commands codes between 0xe4 to 0xf5 and 0xf8 to 0xff). the sensor will return an abort fcs (modified fcs) for reserved commands (command codes 0x02 to 0xdf. the sensor will return an abort fcs (modified fcs) for unused vendor specific test and manufacturing command codes (command codes 0xe8 to 0xef). if any of these types of comm ands exist, they will be disabled during normal operation. malformed commands a malformed command is one which is valid but has an incorrect write or read length for the given command. if a get temperature command with a write length not equal to 1 is sent, then the ASC7521A will send an abort fcs and wait for a new command. an abort fcs will be formed by creating a 1?s complement of the the good fcs. if a get temperature command and the read length is not equal to 2 or 4 then te ASC7521A will send an abort fcs and wait for a stop on the sst bus. see the command summary section for the expected write and read lengt hs of the legal commands. there will be no checking for malformed writereg() and readreg() commands (vendor specific extensions).
- 10 - ? andigilog, inc. 2006 www.andigilog.com october 2006 - 70a05011 ASC7521A command summary hex cmd command name received bytes wr len rd len bytes sent by client - ping() 3(target,wr,rd) 0 0 fcs 0x00 getinttemp() 4(target,wr,rd,cmd) 1 2 fcs/2/fcs 0x01 getexttemp() 4(target,wr,rd,cmd) 1 2 fcs/2/fcs 0x00 getalltemps() 4(target,wr,rd,cmd) 1 4 fcs/4/fcs 0x02-0xdf unsupported abort fcs 0xe0 writereg() 4(target,wr,rd,cmd) 3+ 0 fcs 0xe1 readreg() 4(target,wr,rd,cmd) 2 1+ fcs/1+/fcs 0xe2 vencmdenable() 4(target,wr,rd,cmd) 1 0 fcs 0xe3 vencmddisable() 4(target,wr,rd,cmd) 1 0 fcs 0xe4-0xf5 unsupported abort fcs 0xf6 resetdevice() 4(target,wr,rd,cmd) 1 0 fcs 0xf6 resetdevice() 4(target,wr,rd,cmd) 1 0 none if default address (0x00) 0xf7 getdib() 4(target,wr,rd,cmd) 1 8 fcs/8/fcs 0xf7 getdib() 4(target,wr,rd,cmd) 1 16 fcs/16/fcs 0xf8-0xff unsupported abort fcs table 3. command summary device identifier block (dib) the device identifier block describes the identity and functions of a client device on the sst bus. sixteen bytes are allocated for this function as shown in figure 13. device identifier block is returned by the ASC7521A with a getdib() command. the ASC7521A returned values are shown with the description of each field below. 8 8 16 16 8 vendor id device id device capabilities version/ revision lsb msb lsb msb device interface 8 8 8 16 24 8 function interface device interface extension reserved reserved vendor specific id client device address figure 13. device identifier block device capabilities field (1-byte) msb 6 5 4 3 2 1 lsb address type reserved wake capable alert support suspend support slow device 110 0 0 0 0 0 figure 14. device capabilities field
- 11 - ? andigilog, inc. 2006 www.andigilog.com october 2006 - 70a05011 ASC7521A version / revision field (1-byte) msb 6 5 4 3 2 1 lsb pre- release sst version minor revision 1 001 0000 (default) for v1.0 pre-production 0 001 0000 for v1.0 production figure 15. version / revision field vendor id field (2-bytes) andigilog vendor id is 16 bits = 0x19c9 (this field is stored in the format ls byte, ms byte = 0xc919). vendor ids can be foun d at: http://www.pcisig.com/membership/vid_search device id field (2-bytes) this field uniquely identifies the device from a specific vendor. place the least significant byte as the first byte and the m ost significant byte as the second byte. part number value (ms,ls) stored value (ls,ms) ASC7521A 0x7521 0x2175 device interface field (1-byte) the vendor sets to ?1?, bit positions in this field in the event the device supports higher laye r protocols that are industry s pecific using table 4 . value = 0x02 bit protocol meaning 7 - reserved for future use , must be set = ?0? 6 - reserved for future use , must be set = ?0? 5 ipmi device supports additional access and ca pabilities per the ip mi specification. 4 asf device supports additional access and ca pabilities per the asf specification. 3 serial-ata device supports additional access and capab ilities per the serial-ata specification. 2 pci-express device supports additional access and capabilities per the pci express specification. 1 sst device supports additional access and capabilities per the sst functional descriptor specification (to be published at a future date). 0 oem device supports vendor-specific additiona l access and capabilities per the vendor id and device id. table 4. device interface field function interface field (1-byte) this field provides a mechanism for a device to pass higher-layer sst device-specific information. value = 0x00
- 12 - ? andigilog, inc. 2006 www.andigilog.com october 2006 - 70a05011 ASC7521A device interface extension field (1-byte) this field is used to provide additional information about the device to the upper layers of software. value = 0x00 reserved field (3-bytes) value = 0x00 0x00 0x00 vendor specific id field (1-byte) this field is set by the vendor in a way that uniquely identi fies this device apart from all others with an otherwise common di b content. value = 0x00 ? for fixed address devic es this field may be set to zero. client device address (1-byte) sst client device address is set according to the connection of pins add0 and add1. float is defined as an unconnected pin. add0 add1 address ground ground 0x48 float ground 0x49 v dd ground 0x4a ground float 0x4b float float 0x4c v dd float 0x4d ground v dd 0x4e float v dd 0x4f v dd v dd 0x50
- 13 - ? andigilog, inc. 2006 www.andigilog.com october 2006 - 70a05011 ASC7521A applications information remote diodes the ASC7521A is designed to work with a variety of remote sensors in the form of a diode-connected transistor or the substrate thermal diode of a cpu or graphics controller. actual diodes are not suited for these measurements. there is some variation in the performance of these diodes, described in terms of its departure from the ideal diode equation. this factor is called diode non-ideality, . nf the equation relating diode temperature to a change in thermal diode voltage with two driving currents is: v be = (nf ) kt q ln( n ) where: nf = pentium 4, 65nm non-ideality factor, (nominal 1.009). k = boltzman?s constant, (1.38 x 10 -23 ). t = diode junction temperature in kelvins. q = electron charge (1.6 x 10 -19 coulombs). n = ratio of the two driving currents (10). the ASC7521A is designed and trimmed for an expected value of 1.009, based on the typical value for the pentium 4, 65nm. there is also a tolerance on the value provided. the values for cpus may have different nominal values and tolerances. consult the cpu or gpu manufacturer?s data sheet for the factor. nf nf table 5 gives a representative sample of what one may expect in the range of non-ideality. the trend with cpus is for a lower value with a larger spread. when thermal diode has a non-ideality factor other than 1.0046 the difference in temperature reading at a particular temperature may be interpreted with the following equation: ? ? ? ? ? ? ? ? = actual reported actual n t t 009.1 where: reported t = reported temperature in temperature register. actual t = actual remote diode temperature. actual n = selected diode?s non-ideality factor, . nf temperatures are in kelvins or c + 273.15. this equation assumes that the series resistance of the remote diode 4.52 ?. although the temperature error caused by non-ideality difference is directly proportional to the difference from 1.009, but a small difference in non-ideality results in a relatively large difference in temperature re ading. for example, if there were a 1% tolerance in the non-ideality of a diode it would result in a 2.7 degree difference (at 0c) in the result (0.01 x 273.15). this difference varies with temperature such that a fixed offset value may only be used over a very narrow range. typical correction method required when measuring a wide range of temperature values is to scale the temperature reading in the host firmware. part nf min nf nom nf max series res pentium? iii (cpuid 68h) 1.0057 1.008 1.0125 pentium 4, 130nm 1.001 1.002 1.003 3.64 pentium 4, 90nm 1.011 3.33 pentium 4, 65nm 1.000 1.009 1.050 4.52 intel pentium m 1.001 5 1.0022 1.0029 3.06 2n3904 1.003 1.0046 1.005 0.6 table 5 representative cpu thermal diode and transistor non-ideality factors cpu or asic substrate remote diodes a substrate diode is a parasitic pnp transistor that has its collector tied to ground through the substrate and the base (d-) and emitter (d+) brought out to pins. connection to these pins is shown in figure 16 cpu remote diode connection . the non-ideality figures in table 5 representative cpu thermal diode and transistor non- ideality factors include the effects of any package resistance and represent the value seen from the cpu socket. the temperature indicated will need to be compensated for the departure from a non-ideality of 1.0046 and series resistance of 0.6 ? . figure 16 cpu remote diode connection discrete remote diodes when sensing temperatures other than the cpu or gpu substrate, an npn or pnp transistor may be used. most commonly used are the 2n3904 and 2n3906. these have characteristics similar to the cpu substrate diode with non- ideality around 1.0046. they are connected with base to collector shorted as shown in figure 17 discrete remote diode connection . d+ d- cpu asc7521 substrat e
- 14 - ? andigilog, inc. 2006 www.andigilog.com october 2006 - 70a05011 ASC7521A while it is important to minimi ze the distance to the remote diode to reduce high-frequency noise pickup, they may be located many feet away with proper shielding. shielded, twisted-pair cable is recommended, with the shield connected only at the ASC7521A end as close as possible to the ground pin of the device. figure 17 discrete remote diode connection as with the cpu substrate diode, the temperature reported will be subject to the same errors due to non-ideality variation and series resistance. however, the transistor?s die temperature is usually not the temperature of interest and care must be taken to minimi ze the thermal resistance and physical distance between that temperature and the remote diode. the offset and response time will need to be characterized by the user. series resistance any external series resistance in the connections from the ASC7521A to the cpu pins should be accounted for in interpreting the results of a measurement. the impact of series resistance on the measured temperature is a result of measurement currents developing offset voltages that add to the di ode voltage. this is relatively constant with temperature and may be corrected with a fixed value in the offset register . to determine the temperature impact of resistance is as follows: ?= ? ? ? ? ? ? ? ? = ?= /675.0 /200 135 , c r cv a r t or it r t s sr dvsr where: t r = difference in the temperat ure reading from actual. s r = total series resistance of interconnect (both leads). i d = difference in the two diode current levels (135a). v t = scale of temperature vs. v be (200v/c). for example, a total series resistance of 10 ? would give an offset of +6.75c. board layout considerations the distance between the remote sensor and the ASC7521A should be minimized. all wiring should be defended from high frequency noise sources and a balanced differential layout maintained on d+ and d-. any noise, both common-mode and differential, induced in the remote diode interconnect may result in an offset in the temperature reported. circuit board layout should follow the recommendation of figure 18 . basically, use 10-mil lines and spaces with grounds on each side of the differential pair. choose the ground plane closest to the cpu when using the cpu?s remote diode. figure 18 recommended remote diode circuit board interconnect noise filtering is accomplished by using a bypass capacitor placed as close as possible to the ASC7521A d+ and d- pins. a 1.0nf ceramic capacitor is recommended, but up to 3.3nf may be used. additional filtering takes place within the ASC7521A. it is recommended that the following guidelines be used to minimize noise and achieve highest accuracy: 1. place a 0.1f bypass capacitor to digital ground as close as possible to the power pin of the ASC7521A. 2. match the trace routing of the d+ and d- leads and use a 1.0nf filter capacitor close to the ASC7521A. use ground runs along side the pair to minimize differential coupling as in figure 18 . 3. place the ASC7521A as close to the cpu or gpu remote diode leads as possible to minimize noise and series resistance. 4. avoid running diode connections close to or in parallel with high-speed busses, staying at least 2cm away. 5. avoid running diode connections close to on-board switching power supply inductors. 6. pc board leakage should be minimized by maintaining minimum trace spacing and covering traces over their full length with solder mask. thermal considerations the temperature of the ASC7521A will be close to that of the pc board on which it is mounted. conduction through the leads is the primary path for heat flow. the reported local 10 mils d + 10 mils d - gnd gnd d - 2n3904 d + ASC7521A 2n3906 d + ASC7521A d -
- 15 - ? andigilog, inc. 2006 www.andigilog.com october 2006 - 70a05011 ASC7521A sensor is very close to the circuit board temperature and typically between the board and ambient. in order to measure pc boar d temperature in an area of interest, such as the area around the cpu where voltage regulator components generate significant heat, a remote diode-connected transistor should be used. a surface-mount sot-23 or sot-223 is recommended. the small size is advantageous in minimizing response time because of its low thermal mass, but at the same time it has low surface area and a high thermal resistance to ambient air. a compromise must be achieved between minimizing thermal mass and increasing the surface area to lower the junction-to-ambient thermal resistance. in order to sense temperature of air-flows near board- mounted heat sources, such as memory modules, the sensor should be mounted above the pc board. a to-92 packaged transistor is recommended. the power consumption of the ASC7521A is relatively low and should have little self-heating effect on the local sensor reading. at the highest measur ement rate the dissipation is less than 2mw, resulting in only a few tenths of a degree rise.
- 16 - ? andigilog, inc. 2006 www.andigilog.com october 2006 - 70a05011 ASC7521A m8 package ? 8-lead msop package dimensions pb-free package 2.85mm (min) 3.05mm (max) 4.75mm (min) 5.05mm (max) 0.95mm bsc 2.90mm (min) 3.10mm (max) 0.25mm (min) 0.40mm (max) 2.90mm (min) 3.10mm (max) 4.75mm (min) 5.05mm (max) 0.65mm bsc 1.10mm (max) 0.525mm bsc 0 (min) 6 (max) 2.85mm (min) 3.05mm (max) 0.10mm 0.78mm (min) 0.94mm (max) 0.05mm (min) 0.15mm (max) 2.90mm (min) 3.10mm (max) a a 0.25mm (min) 0.40mm (max) 0.25mm (min) 0.35mm (max) 0.13mm (min) 0.23mm (max) 0.13mm (min) 0.18mm (max) 0 (min) 6 (max) 9 (min) 15 (max) 0.40mm (min) 0.70mm (max) detail b section a detail b
andigilog, inc. 8380 s. kyrene rd., suite 101 tempe, arizona 85284 tel: (480) 940-6200 fax: (480) 940-4255 - 17 - ? andigilog, inc. 2006 www.andigilog.com october 2006 - 70a05011 ASC7521A notes:
andigilog, inc. 8380 s. kyrene rd., suite 101 tempe, arizona 85284 tel: (480) 940-6200 fax: (480) 940-4255 - 18 - ? andigilog, inc. 2006 www.andigilog.com october 2006 - 70a05011 ASC7521A data sheet classifications preliminary specification this classification is shown on the heading of each page of a specification for produc ts that are either under development (design and qualificat ion), or in the formative planning stages. andigilog reserves the right to change or discontinue these products without notice. new release specification this classification is shown on the heading of the first page onl y of a specification for prod ucts that are either under the later stages of development (characte rization and qualification), or in the early weeks of release to production. andigilog reserves the right to c hange the specification and information for these products without notice. fully released specification fully released datasheets do not contain any classifica tion in the first page header. these documents contain specification on products t hat are in full production. andigilog will no t change any guaranteed limits without written notice to the customers. obsolete datasheets that were written prior to january 1, 2001 without any header classification information should be considered as obsolete and non-active specifications, or in the best case as preliminary specifications. pentium? is a trademark of intel corporation life support policy andigilog's products are not authorized for use as critical components in life support devices or systems without the express written approval of the president and general counsel of andigilog, inc. as used herein: 1. life support devices or systems are dev ices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in th e labeling, can be reasonably expected to result in a significant injury to the user. 2. a critical component is any component of a life support devic e or system whose failure to perform can be reasonably expecte d to cause the failure of the life support device or sy stem, or to affect its safety or effectiveness.

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