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1c temperature monitor with series resistance cancellation ADT7461 rev. a in fo rmation furn ished by an alog d e v i c e s is believed to be accurate and reliable. how e ver, n o resp on sibili ty is assume d b y a n alog de vices fo r its use, nor for an y i n fri n geme nt s of p a t e nt s or ot h e r ri ght s o f th ird parties th at may result fro m its use . specifications subjec t to chan g e witho u t n o tice. no licen s e is g r an te d by implicati o n or ot herwi s e u n der a n y p a t e nt or p a t e nt ri ghts of analog de v i ces. trademarks an d registered tra d ema r ks are the prop erty o f their respective ow ners. one technolog y way, p.o . box 9106, norwood, ma 02062-9106, u.s.a. t e l: 781. 329. 4 700 www.analog.com fax: 781. 326. 87 03 ? 2004 analog de vices, i n c. al l r i ght s r e ser v ed . features on-chip and remote temperature sensor 0.25c resolu tion/1c accu racy on remote channel 1c resolu tion/3c accu racy on local channel automaticall y cancels up to 3 k? (typ) of resi stance in series with remote di ode to allow n o ise filtering extended, swit chable temperature me asure m ent range 0 c to +127 c (d ef ault) or C5 5c t o +150 c pin- and regist er-compatible with adm10 32 2-wire smbus s e rial interf ace with smbus ale r t support programmable over/under t e mperature limi ts offset register s for system cal i bration up to two overtemperature f a il-safe therm ou tpu t s small 8 - lea d s o ic or msop package 170 a operati n g current, 5.5 a standby c u r r ent applic ati o ns deskto p and n o tebo o k co mputers industrial cont rollers smart batterie s automotive enbedded syst ems burn-in applications instrumentation general description the ad t7461 1 i s a d u al- c h a nn e l d i gi ta l th e r m o m e t e r a n d un der / o v er te m p er a t ur e a l a r m, in te nde d fo r us e in pc s an d t h er mal ma na gem e n t syst em s. i t is p i n- an d r e g i s t er -com p a t i ble wi t h t h e ad m1 032. th e adt7 461 has thr e e addi tional f e a t ur es: ser i es r e sis t a n ce can c e lla tio n (w h e r e u p t o 3 k? (typ ical) o f r e sis t a n c e in s e r i es w i t h t h e tem p era t ur e m o ni to r i n g dio d e ma y b e a u t o ma t i cal l y ca n c e l le d f r om t h e t e m p er a t ur e r e s u l t , al lo win g n o is e f i lt er in g); co nf igura b le aler t o u t p ut; a nd an ex tende d , sw i t chab le t e m p era t ur e m e as ur e m e n t ra n g e . the ad t7461 c a n acc u ra t e l y meas ur e the t e m p era t ur e o f a r e m o t e t h er mal dio d e t o 1c and t h e am b i en t t e m p era t ur e t o 3c. the t e m p era t ur e m e as ur e m e n t ra n g e def a u l ts t o 0c t o +127c, co m p a t i b le wi th t h e ad m1032, b u t c a n b e s w i t ch ed to a wider m e as urem en t ra n g e o f ?55c t o +150c. the ad t746 1 co mm uni c a t es o v er a 2-wir e s e r i al in ter f ace com p a t i b le w i t h sys t em ma na g e m e n t b u s (s mb us) s t a nda r d s. a n aler t output s i g n a l s w h e n t h e on - c h i p or re mot e te m p e r a t u r e i s out of r a nge. the therm output i s a c o m p ar ator output t h at a l l o w s on / o f f co n t r o l o f a co olin g fa n. the aler t o u t p ut can b e r e c o nf igur e d as a s e cond therm o u t p u t , if r e q u ir e d . 1 pr otected by u. s. patents 5,195,827; 5,867,012; 5,982,221; 6,097,239; 6,133,753; 6,169,442; othe r patents pending. 04110- 0- 012 dig i tal mux dig i tal mux sclk sdata gnd v dd 6 4 address pointer register local temperature low limit register local temperature high limit register remote temperature low limit register remote temperature high limit register limit co mparato r local temperature value register remote temperature value register adc analog mux on-chip temperature sensor run/standby busy remote offset register external diode open-circuit ADT7461 status register smbus interface local therm limit register external therm limit register configuration register interrupt masking 7 5 1 8 therm alert/ therm2 d+ d? src block 2 3 conversion rate register f i gur e 1 . f u nctio n al bl oc k dia g r a m
ADT7461 rev. a | page 2 of 24 table of contents specifications ....................................................................................3 smbus timing specifications ........................................................4 absolute maximum ratings ...........................................................5 esd caution .................................................................................5 pin configuration and function descriptions ............................6 typical performance characteristics ............................................7 functional description ...................................................................9 series resistance cancellation ...................................................9 temperature measurement method .........................................9 temperature measurement results .........................................10 temperature measurement range ..........................................10 temperature data format ........................................................10 ADT7461 registers ...................................................................11 serial bus interface ....................................................................14 addressing the device ..............................................................14 alert output ...........................................................................16 low power standby mode ........................................................16 sensor fault detection .............................................................16 the ADT7461 interrupt system ..............................................16 application information ..........................................................18 factors affecting diode accuracy ..........................................18 thermal inertia and self-heating ...........................................18 layout considerations ..............................................................19 application circuit ....................................................................20 outline dimensions ......................................................................21 ordering guide .........................................................................21 revision history 10/04changed from rev. 0 to rev. a change to smbus specifications................................................4 changes to figure 6 and figure 10............................................7 added figure 9 and figure 13....................................................7 changes to temperature measurement section ....................10 changes to figure 19 and figure 25........................................16 changes to serial bus interface section..................................14 10/03revision 0: initial version
ADT7461 rev. a | page 3 of 24 specifications t a = ?40c to +120c, v dd = 3 v to 5.5 v, unless otherwise noted. table 1. parameter min typ max unit test conditions power supply supply voltage, v dd 3.0 3.30 5.5 v average operating supply current, i dd 170 215 a 0.0625 conversions/sec rate 1 5.5 10 a standby mode , C40c t a +85c 5.5 20 a standby mode, +85c t a +120c undervoltage lockout thresh old 2.2 2.55 2.8 v v dd input, disables adc, rising edge power-on-reset threshold 1 2.5 v temperature-to-digital converter local sensor accuracy 1 3 c ?40c t a +100c, 3 v v dd 3.6 v resolution 1 c remote diode sensor accuracy 1 c +60c t a +100c, ?55c t d 2 +150c, 3 v v dd 3.6 v 3 c ?40c t a +120c, ?55c t d 2 +150c, 3 v v dd 5.5 v resolution 0.25 c remote sensor source current 96 a high level 3 36 a middle level 3 6 a low level 3 conversion time 32.13 114.6 ms from stop bit to conversion complete (both channels), one- shot mode with averaging switched on 3.2 12.56 ms one-shot mode with averaging off (i.e., conversion rate = 16, 32, or 64 conversions per second) maximum series resistance cancelled 3 k? resistance split evenly on both the d+ and dC inputs open-drain digital outputs ( therm , alert / therm2 ) output low voltage, v ol 0.4 v i out = ?6.0 ma 3 high level output leakage current, i oh 0.1 1 a v out = v dd 3 alert output low sink current 1 ma alert forced to 0.4 v smbus interface 3, 4 logic input high voltage, v ih 2.1 v 3 v v dd 3.6 v sclk, sdata logic input low voltage, v il 0.8 v 3 v v dd 3.6 v sclk, sdata hysteresis 500 mv smbus output low sink current 6 ma sdata forced to 0.6 v logic input current, i ih , i il ?1 +1 a smbus input capacitance, sclk, sdata 5 pf smbus clock frequency 400 khz smbus timeout 5 25 64 ms user programmable sclk falling edge to sdata valid time 1 s master clocking in data 1 see for information on other conversion rates. table 8 2 guaranteed by characterization, but not production tested. 3 guaranteed by design, but not production tested. 4 see section for more information. smbus timing specifications 5 disabled by default. details on how to enable it are in the smbus section of this data sheet.
ADT7461 r e v. a | pa ge 4 o f 2 4 smbus timing specifications table 2. s m bus timing s p ecifications 1 parameter limit at t min an d t ma x u n i t d e s c r i p t i o n f sclk 400 khz max t low 1.3 s min clock l o w pe rio d , between 10% points t high 0.6 s min clock hig h perio d , between 90% points t r 300 ns max clock/data rise time t f 300 ns max clock/data fall ti me t su ; s t a 600 ns min start condition setup time t hd; sta 2 600 ns min start condition hold time t su ; da t 3 100 ns min data setup time t hd; dat 300 ns min data hold time t su ; s t o 4 600 ns min stop condition setup time t bu f 1.3 s min bus bree time between stop a n d start conditions 1 guarante e d by d e sign, but no t pro d uctio n te s t e d . 2 ti m e fr om 10% of sd ata t o 90% of s c lk. 3 ti m e f o r 10% or 90% of sd ata t o 10% of s c lk. 4 ti m e f o r 90% of s c lk t o 10% of sd ata. 04110-0-001 sclk sdata t r t f t low t hd;dat t hd;sta t high t su;dat stop start stop start t su;sta t su;sto t hd;sta t buf f i gure 2. s e r i al bus t i ming
ADT7461 r e v. a | pa ge 5 o f 2 4 absolute maximum ratings table 3. p a r a m e t e r r a t i n g positive supply voltage (v dd ) to gnd ?0.3 v, +5.5 v d+ ?0.3 v to v dd + 0.3 v d? to gnd ?0.3 v to +0.6 v sclk, sdata, alert ?0.3 v to +5.5 v ther m ?0.3 v to v dd + 0.3 v input current, s d ata, ther m ?1 ma, +50 ma input current, d ? 1 ma esd rating, all p i ns (human body model) 2000 v maximum junction temperature (t j max) 150c storage temperature range ?65c to +150c ir reflow peak temperature 220c pb-free parts only 260c (0.5c) lead temperature (soldering 10 sec) 300c ther m al c h a r act e ris t ics 8-l e ad so i c p a c k a g e ja = 121c/w 8-l e ad mso p p a c k a g e ja = 142c/w s t r e s s es a b o v e t h os e lis t e d u n de r a b s o l u t e m a xi m u m r a t i n g s ma y c a us e p e r m a n en t dama ge t o t h e de vice . this is a s t r e s s r a t i ng o n ly ; f u nc t i on a l op e r a t i o n of t h e d e v i c e a t t h e s e or a n y o t h e r con d i t io ns a b o v e t h o s e i ndic a te d i n t h e op er a t io na l s e c t io n o f t h is sp e c if ic a t io n is no t im plie d . e x p o sur e t o a b s o l u te max i m u m ra t i ng co ndi t i on s fo r ex ten d e d p e r i o d s ma y a f fe c t de vice r e l i ab i l i t y . esd caution esd (electrostatic discharge) sensitive device. ele c tros tatic charg e s as high as 4000 v readily accumulate on the human body and test eq uipment and can discharge wi thout detection. although this product features proprietary esd protection circu i try, permanent dama ge may occur on devices subjected to high energy electrostatic discharges. theref ore, prop er esd precautions a r e recommended to avoid perform a nce degradation or l o ss of functiona l ity.
ADT7461 r e v. a | pa ge 6 o f 2 4 pin conf iguration and fu nction descriptions 04110-0-013 sclk sdata alert/therm2 gnd 1 v dd ADT7461 top view (not to scale) 8 2 d+ 7 3 d? 6 4 therm 5 f i gure 3. pin config ur ation ta ble 4. pi n f u nct i on d e s c ri pt i o ns pin no. mnemonic description 1 v dd positive supply, 3 v to 5.5 v. 2 d+ positive conne c t ion to remote temperature sensor. 3 d? negative conne ction to remote temperature sensor. 4 ther m open-drain output that can be used to turn a fa n on /off or throt t le a cpu clock i n the event of an overtemperatur e condition. requires pull-up to v dd . 5 gnd supply ground connectio n. 6 alert / ther m2 open-drain logic output used as interrupt or smbus al ert. this may also be c o nfigured as a second ther m output. req u ire s pull-up resistor. 7 sdata logic input/ output, smbus seri al data . open-drain output. re q u ires pull-up resistor. 8 sclk logic input, smbus serial cl ock. requires pull-u p resistor.
ADT7461 r e v. a | pa ge 7 o f 2 4 typical perf orm ance cha r acte ristics 04110-0-017 60 0 2 0 4 06 08 0 leakage resistance (m ? ) 100 te mp e rature e rror ( c) ?80 ?60 ?40 ?20 0 20 40 d+ to gnd d+ to v cc f i gure 4. t e mper at ur e e r ror v s . l e aka g e r e sistance 04110-0-022 ?3 ?10 1 0 3 0 5 0 7 0 9 0 110 130 150 temperature ( c) te mp e rature e rror ( c) ?0.8 ?0.7 ?0.6 ?0.5 ?0.4 ?0.3 ?0.2 ?0.1 0 f i g u re 5. t e mper at ur e e r ror v s . ac t u a l t e m p er at ure u s ing 2n 39 06 04110-0-027 4 0 100 200 300 frequency (mhz) 400 500 600 te mp e rature e rror ( c) ?2 ?1 0 1 2 3 40mv no filter 60mv no filter 40mv with filter 60mv with filter f i gure 6. t e mper at ur e e r ror v s . d i ffe r e ntia l mod e n o is e f r equenc y ( w it h and w i t h out r- c-r f ilte r of 1 0 0 ?C 2. 2 nfC 1 0 0 ?) 04110-0-015 20 02 0 frequency (mhz) 40 te mp e rature e rror ( c) ?15 ?10 ?5 0 5 10 15 250mv external 250mv internal 100mv external 100mv internal f i gure 7. t e mper at ur e e r ror v s . p o w e r sup p ly n o ise f r equ e nc y 04110-0-018 0 0 5 10 15 20 capacitance (nf) 25 te mp e rature e rror ( c) ?70 ?60 ?50 ?40 ?30 ?20 ?10 f i gure 8. t e mper at ur e e r ror v s . cap a c i tanc e b e t w een d+ and d ? 04110-0-024 180 160 140 120 100 0 100 200 300 frequency (mhz) 400 500 600 te mp e rature e rror ( c) 80 60 40 20 0 ?20 100mv no filter 100mv with filter f i gure 9. t e mper at ur e e r ror v s . 1 0 0 m v d i fferenti a l m o de no is e f r equ e nc y ( w it h and w i t h out r- c-r f ilte r of 1 0 0 ?C 2. 2 nfC 1 0 0 ?)
ADT7461 r e v. a | pa ge 8 o f 2 4 04110-0-025 5 0 100 200 300 frequency (mhz) 400 500 600 te mp e rature e rror ( c) ?1 0 1 2 3 4 40mv no filter 60mv no filter 40mv with filter 60mv with filter f i gure 10. t e mpe r a t ur e e r r o r v s . co m m o n -mode n o ise f r equ e nc y ( w it h and w i t h out r- c-r f ilte r of 1 0 0 ?C 2. 2 nfC 1 0 0 ?) 04110-0-020 40 0 100 200 300 3v 5.5v scl clock frequency (khz) 400 50 150 250 350 i dd ( a) 0 5 10 15 20 25 30 35 f i gure 1 1 . sta n db y sup p l y c u rrent vs . cl ock f r equenc y 04110-0-021 7 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 5.4 v dd (v) i dd ( a) 0 1 2 3 4 5 6 f i gure 12. standby current v s . sup p ly v o ltag e 04110-0-026 55 45 35 25 15 5 0 100 200 300 frequency (mhz) 400 500 600 te mp e rature e rror ( c) ?5 100mv no filter 100mv with filter f i gure 13. t e mpe r a t ur e e r r o r v s . 1 0 0 m v co mm on-m ode nois e f r eque nc y ( w it h and w i t h out r- c-r f ilte r of 1 0 0 ?C 2. 2 nfC 1 0 0 ?) 04110-0-019 800 0.01 0.1 1 1 0 3v 5.5v conversion rate (hz) 100 i dd ( a) 0 100 200 300 400 500 600 700 f i gure 14. o p er atin g sup p ly cu rrent v s . con v e r s i on r a te 04110-0-023 0 2 10 200 1k 2k 3k 4k series resistance ( ? ) te mp e rature e rror ( c) ?5 0 5 10 15 20 25 30 35 40 45 50 3.3v t = ? 30 3.3v t = +25 3.3v t = +120 5.5v t = ? 30 5.5v t = +25 5.5v t = +120 f i gure 15. t e mpe r a t ur e e r r o r v s . s e ri es r e s i s t anc e
ADT7461 rev. a | page 9 of 24 functional description the ADT7461 is a local and remote temperature sensor and over/under temperature alarm, with the added ability to auto- matically cancel the effect of 3 k? (typical) of resistance in series with the temperature monitoring diode. when the ADT7461 is operating normally, the on-board adc operates in a free-running mode. the analog input multiplexer alternately selects either the on-chip temperature sensor to measure its local temperature or the remote temperature sensor. the adc digitizes these signals and the results are stored in the local and remote temperature value registers. the local and remote measurement results are compared with the corresponding high, low, and therm temperature limits, stored in eight on-chip registers. out-of-limit comparisons generate flags that are stored in the status register. a result that exceeds the high temperature limit, the low temperature limit, or an external diode fault will cause the alert output to assert low. exceeding therm temperature limits causes the therm output to assert low. the alert output can be reprogrammed as a second therm output. the limit registers can be programmed and the device con- trolled and configured via the serial smbus. the contents of any register can also be read back via the smbus. control and configuration functions consist of switching the device between normal operation and standby mode, selecting the temperature measurement scale, masking or enabling the alert output, switching pin 6 between alert and therm2 , and selecting the conversion rate. series resistance cancellation parasitic resistance to the d+ and d? inputs to the ADT7461, seen in series with the remote diode, is caused by a variety of factors, including pcb track resistance and track length. this series resistance appears as a temperature offset in the remote sensors temperature measurement. this error typically causes a 0.5c offset per ohm of parasitic resistance in series with the remote diode. the ADT7461 automatically cancels out the effect of this series resistance on the temperature reading, giving a more accurate result, without the need for user characterization of this resis- tance. the ADT7461 is designed to automatically cancel typically up to 3 k? of resistance. by using an advanced temperature measurement method, this is transparent to the user. this feature allows resistances to be added to the sensor path to produce a filter, allowing the part to be used in noisy environ- ments. see the section on noise filtering for more details. temperature measurement method a simple method of measuring temperature is to exploit the negative temperature coefficient of a diode, measuring the base-emitter voltage (v be ) of a transistor operated at constant current. however, this technique requires calibration to null out the effect of the absolute value of v be , which varies from device to device. the technique used in the ADT7461 is to measure the change in v be when the device is operated at three different currents. previous devices have used only two operating currents, but it is the use of a third current that allows automatic cancellation of resistances in series with the external temperature sensor. figure 16 shows the input signal conditioning used to measure the output of an external temperature sensor. this figure shows the external sensor as a substrate transistor, but it could equally be a discrete transistor. if a discrete transistor is used, the collec- tor will not be grounded and should be linked to the base. to prevent ground noise interfering with the measurement, the more negative terminal of the sensor is not referenced to ground, but is biased above ground by an internal diode at the d? input. c1 may be added as a noise filter (a recommended maximum value of 1,000 pf). however, a better option in noisy environments is to add a filter, as described in the noise filtering section. see the layout considerations section for more information on c1. to me a su re ? v be , the operating current through the sensor is switched among three related currents. shown in figure 16, n1 i and n2 i are different multiples of the current, i. the currents through the temperature diode are switched between i and n1 i, giving ?v be1 , and then between i and n2 i, giving ?v be2 . the temperature may then be calculated using the two ?v be measurements. this method can also be shown to cancel the effect of any series resistance on the temperature measurement. the resulting ?v be waveforms are passed through a 65 khz low-pass filter to remove noise and then to a chopper-stabilized amplifier. this amplifies and rectifies the waveform to produce a dc voltage proportional to ?v be . the adc digitizes this vol- tage and a temperature measurement is produced. to reduce the effects of noise, digital filtering is performed by averaging the results of 16 measurement cycles for low conversion rates. at rates of 16, 32, and 64 conversions/second, no digital averaging takes place. signal conditioning and measurement of the internal tempera- ture sensor is performed in the same manner.
ADT7461 rev. a | page 10 of 24 04110-0-002 i n1 in 2 i i bias v dd v out+ to adc v out? remote sensing transistor *capacitor c1 is optional. it should only be used in noisy environments. d+ d? c1* bias diode low-pass filter f c = 65khz f i gure 1 6 . input s i gna l c o nd i t io n i ng temperature measurement results the r e s u l t s o f t h e lo c a l an d r e m o te t e m p er a t u r e m e as ur emen t s a r e s t o r e d in t h e lo cal an d r e m o t e t e m p er a t ur e val u e r e g i s t ers a nd a r e com p a r e d wi t h limi ts p r og ra mm e d in to th e lo cal and r e m o t e hig h and lo w limi t r e g i st ers. the lo cal tem p e r a t ur e val u e is i n r e g i s t er 0x00 a nd has a r e s o - l u t i o n o f 1c. th e ext e r n al t e m p era t ur e val u e i s s t o r e d i n tw o r e g i s t ers, w i t h t h e up p e r b y t e i n r e g i s t er 0x01 a nd t h e lo w e r b y t e in r e g i s t er 0x10. onl y t h e t w o ms bs in t h e ext e r n al t e m p - era t ur e lo w b y t e a r e us e d . this g i v e s t h e exter n al t e m p era t ur e m e as ur em en t a r e s o l u tio n o f 0.25c. t a b l e 5 sho w s th e da ta fo r m a t fo r t h e ext e r n al t e m p er a t ur e lo w b y t e . table 5. exte nded te mperature resolution ( r emote tem p erature l o w byte) extended re solution remote temperature low byt e 0.00c 0 000 0000 0.25c 0 100 0000 0.50c 1 000 0000 0.75c 1 100 0000 w h en r e adin g t h e f u l l ext e r n al t e m p era t ur e val u e , b o t h t h e hig h a nd lo w b y t e , t h e tw o r e g i s t ers sh o u ld b e r e ad i n s u cces sion. readin g on e r e g i s t er do es n o t l o c k the o t h e r , s o bo th sh o u ld b e r e ad b e fo r e t h e n e xt con v ersio n f i nis h es. i n p r ac t i ce , t h er e is m o r e th a n en o u gh tim e t o r e ad bo th r e gis t e r s, as tra n sa cti o n s o v er t h e s m bus a r e sig n if ican t l y fas t er t h a n a c o n v ersio n t i m e . temperature measurement range the t e m p er a t ure m e as ur e m en t ra n g e fo r b o t h i n t e r n al an d ext e r n al m e as ur em en ts is, b y defa u l t, 0c t o +127c. h o w e v e r , th e ADT7461 c a n be o p er a t e d usin g a n ext e n d ed t e m p er a t ur e ra n g e . i t can m e as ur e t h e f u l l t e m p er a t ur e ra n g e o f a n ext e r n al dio d e , f r o m ?55 c t o +150c. th e us er can s w i t c h between t h es e tw o t e m p era t ur e ra n g es b y s e t t in g o r cle a r i n g bi t 2 in t h e co nf igura t io n r e g i st er . a va lid r e su l t is a v a i lab l e in t h e n e xt m e as ur e m en t c y cle a f t e r cha n g i n g t h e t e m p er a t ur e ra n g e . i n ext e n d e d t e m p er a t ur e m o de , t h e u p p e r an d lo w e r t e m p - era t ur e tha t c a n be m e as ur ed b y th e ad t7461 is limi ted b y t h e r e m o t e dio d e s e le c t io n. th e t e m p era t ur e r e g i s t e r s t h em s e l v es ca n ha v e val u es f r o m ?64c t o +191c. h o w e ver , m o s t t e m p - era t ur e s e n s in g dio d es ha v e a maxim u m t e m p er a t ur e ra n g e o f ?55c t o +150c. a b o v e 1 5 0 c , th e y m a y l o se th e i r se m i c o n - d u c t o r ch a r ac t e r i st ic s and a p p r o x im a t e c o nd uc to rs inst e a d . th is r e s u l t s in a di o d e sh o r t. i n t h is c a s e , a re ad o f t h e t e m p er a t ure r e s u l t r e g i ster w i l l g i ve t h e l a st go o d te m p er a t ure me as ure m e n t. the us er sh ou l d b e a w a r e t h a t t h e t e m p er a t ur e me as ur e m e n t on t h e exter n al channe l ma y no t b e acc u r a te fo r t e m p er a t ur es t h a t a r e o u tsi d e t h e op er a t i n g ran g e of t h e r e mo te s e ns o r . i t s h o u ld be n o t e d tha t whil e bo th lo cal a n d r e m o t e t e m p era t ur e m e as ur em en ts ca n b e made w h i l e t h e p a r t is in e x t e n d e d t e m p - era t ur e m o de , th e ad t7461 i t s e lf s h o u ld n o t be exp o s e d t o t e m p - era t ur es g r e a t e r tha n t h os e s p e c i f i e d in t h e a b sol u t e maxim u m ra t i n g s s e ct io n . f u r t h e r , t h e de vice is o n l y gua r a n t e e d t o o p era t e a s s p e c if i e d a t a m b i en t t e m p era t ur es f r o m ?40c t o +120c. temperature data format the ad t7461 has tw o t e m p era t ur e da ta f o r m a t s. w h en t h e t e m p era t ur e m e as ur emen t ran g e is f r o m 0c t o +127c (defa u l t ), t h e t e m p er a t ur e da t a fo r m a t fo r b o t h in t e r n al and ext e r n al t e m p er a t ur e r e s u l t s is b i na r y . w h e n t h e m e as ur emen t ra n g e is in exte n d e d m o d e , a n o f fs et b i na r y da t a fo r m a t is us e d fo r b o t h in t e r n a l a nd ext e r n al r e s u l t s. t e m p era t ur e val u es in t h e o f fs et b i na r y da t a fo r m a t a r e o f fs et b y 64c. e x a m ples o f t e m p - era t ur es i n b o t h da t a fo r m a t s a r e s h own in t a b l e 6. table 6. temp erature data format (local and remote tem p erature high byte) temperature binary offset binary 1 C55c 0 000 0000 2 0 000 1001 0c 0 000 0000 0 100 0000 +1c 0 000 0001 0 100 0001 +10c 0 000 1010 0 100 1010 +25c 0 001 1001 0 101 1001 +50c 0 011 0010 0 111 0010 +75c 0 100 1011 1 000 1011 +100c 0 110 0100 1 010 0100 +125c 0 111 1101 1 011 1101 +127c 0 111 1111 1 011 1111 +150c 0 111 1111 3 1 101 0110 1 off s et bi n a ry sca l e t e m p era t ure va lue s a r e of fs et by 64 c. 2 binary s c ale temp. meas urement retur n s 0c for a l l tempe r atures < 0 c. 3 binary scale temp. measurement retur n s 127c for all tem p erature > 127c.
ADT7461 rev. a | page 11 of 24 the user may switch between measurement ranges at any time. switching the range will also switch the data format. the next temperature result following the switching will be reported back to the register in the new format. however, the contents of the limit registers will not change. it is up to the user to ensure that when the data format changes, the limit registers are repro- grammed as necessary. more information on this can be found in the limit registers section. ADT7461 registers the ADT7461 contains 22 8-bit registers in total. these regis- ters are used to store the results of remote and local temperature measurements and high and low temperature limits and to confi- gure and control the device. a description of these registers fol- lows. additional details are given in table 7 through table 11. address pointer register the address pointer register itself does not have or require an address, as the first byte of every write operation is automa- tically written to this register. the data in this first byte always contains the address of another register on the ADT7461, which is stored in the address pointer register. it is to this register address that the second byte of a write operation is written to or to which a subsequent read operation is performed. the power-on default value of the address pointer register is 0x00, so if a read operation is performed immediately after power-on, without first writing to the address pointer, the value of the local temperature will be returned, since its register address is 0x00. temperature value registers the ADT7461 has three registers to store the results of local and remote temperature measurements. these registers can only be written to by the adc and can be read by the user over the smbus. the local temperature value register is at address 0x00. the external temperature value high byte register is at address 0x01, with the low byte register at address 0x10. the power-on default for all three registers is 0x00. configuration register the configuration register is address 0x03 at read and address 0x09 at write. its power-on default is 0x00. only four bits of the configuration register are used. bits 0, 1, 3, and 4 are reserved and should not be written to by the user. bit 7 of the configuration register is used to mask the alert output. if bit 7 is 0, the alert output is enabled. this is the power-on default. if bit 7 is set to 1, the alert output is disabled. this only applies if pin 6 is configured as alert . if pin 6 is configured as therm2 , then the value of bit 7 has no effect. if bit 6 is set to 0, which is power-on default, the device is in operating mode with the adc converting. if bit 6 is set to 1, the device is in standby mode and the adc does not convert. the smbus does, however, remain active in standby mode, so values can be read from or written to the ADT7461 via the smbus in this mode. the alert and therm outputs are also active in standby mode. changes made to the registers in standby mode that affect the therm or alert outputs will cause these signals to be updated. bit 5 determines the configuration of pin 6 on the ADT7461. if bit 5 is 0, (default) then pin 6 is configured as an alert output. if bit 5 is 1, then pin 6 is configured as a therm2 output. bit 7, the alert mask bit, is only active when pin 6 is configured as an alert output. if pin 6 is setup as a therm2 output, then bit 7 has no effect. bit 2 sets the temperature measurement range. if bit 2 is 0 (default value), the temperature measurement range is set between 0c to +127c. setting bit 2 to 1 means that the measurement range is set to the extended temperature range. table 7. configuration register bit assignments bit name function power-on default 7 mask1 0 = alert enabled 1 = alert masked 0 6 run/stop 0 = run 1 = standby 0 5 alert / therm2 0 = alert 1 = therm2 0 4C3 reserved 0 2 temperature range select 0 = 0c to 127c 1 = extended range 0 1C0 reserved 0 conversion rate register the conversion rate register is address 0x04 at read and address 0x0a at write. the lowest four bits of this register are used to program the conversion rate by dividing the internal oscillator clock by 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, or 1024 to give conversion times from 15.5 ms (code 0x0a) to 16 seconds (code 0x00). for example, a conversion rate of 8 conversions per second means that beginning at 125 ms intervals the device performs a conversion on the internal and the external temperature channels. this register can be written to and read back over the smbus. the higher four bits of this register are unused and must be set to 0. the default value of this register is 0x08, giving a rate of 16 conversions per second. use of slower conversion times greatly reduces the device power consumption, as shown in table 8.
ADT7461 rev. a | page 12 of 24 table 8. conversion rate register codes code conversion/second average supply current a typ at v dd = 5.5 v 0x00 0.0625 121.33 0x01 0.125 128.54 0x02 0.25 131.59 0x03 0.5 146.15 0x04 1 169.14 0x05 2 233.12 0x06 4 347.42 0x07 8 638.07 0x08 16 252.44 0x09 32 417.58 0x0a 64 816.87 0x0b to 0xff reserved limit registers the adt has eight limit registers high lo and ter temperature limits for oth local and remote temperature measurements the remote temperature high and lo limits span to registers each to contain an upper and loer te for each limit there is also a ter hsteresis register all limit registers can e ritten to and read ac over the sus see tale for details of the limit registers addresses and their poer-on default values hen pin is configured as an alert output the high limit registers perform a comparison hile the lo limit registers perform a comparison for eample if the high limit register is programmed ith c then measuring c ill result in an out-of-limit condition setting a flag in the status register f the lo limit register is programmed ith c measuring c or loer ill result in an out-of-limit condition eceeding either the local or remote ter limit asserts ter lo hen pin is configured as ter eceeding either the local or remote high limit asserts ter lo a default hsteresis value of c is provided that applies to oth ter channels this hsteresis value ma e reprogrammed to an value after poer-up register address t is important to rememer that the temperature limits data format is the same as the temperature measurement data format so if the temperature measurement uses default inar then the temperature limits also use the inar scale f the temperature measurement scale is sitched hoever the temperature limits do not sitch automaticall the user must reprogram the limit registers to the desired value in the correct data format for eample if the remote lo limit is set at c and the default inar scale is eing used the limit register value should e f the scale is sitched to offset inar the value in the lo temperature limit register should e reprogrammed to e status register the status register is a read-onl register at address t contains status information for the adt it of the status register indicates that the adc is us con- verting hen it is high the other its in this register flag the out-of-limit temperature measurements its to and its to and the remote sensor open circuit it f pin is configured as an alert output the folloing applies f the local temperature measurement eceeds its limits it high limit or it lo limit of the status register asserts to flag this condition f the remote temperature measurement eceeds its limits then it high limit or it lo limit asserts it asserts to flag an open-circuit condition on the remote sensor these five flags are nord together so if an of them is high the alert interrupt latch ill e set and the alert output ill go lo reading the status register clears the five flags its to pro- vided the error conditions causing the flags to e set have gone aa a flag it can e reset onl if the corresponding value reg- ister contains an in-limit measurement or if the sensor is good the alert interrupt latch is not reset reading the status register t resets hen the alert output has een serviced the master reading the device address provided the error condi- tion has gone aa and the status register flag its are reset hen flag andor flag are set the ter output goes lo to indicate that the temperature measurements are outside the programmed limits the ter output does not need to e reset unlie the alert output once the measurements are ithin the limits the corresponding status register its are reset automaticall and the ter output goes high the user ma add hsteresis programming register the ter output ill e reset onl hen the temperature falls to limit valuehsteresis value hen pin is configured as ter onl the high temp- erature limits are relevant f flag andor flag are set the ter output goes lo to indicate that the temperature measurements are outside the programmed limits flag and flag have no effect on ter the ehavior of ter is otherise the same as ter table 9. status register bit assignments bit name function 7 busy 1 when adc converting 6 lhigh* 1 when local high temperature limit tripped 5 llow* 1 when local low temperature limit tripped 4 rhigh* 1 when remote high temperature limit tripped 3 rlow* 1 when remote low temperature limit tripped 2 open* 1 when remote sensor open circuit 1 rthrm 1 when remote therm limit tripped 0 lthrm 1 when local therm limit tripped *these flags stay high until the status register is read or they are reset by por.
ADT7461 rev. a | page 13 of 24 offset register offset errors may be introduced into the remote temperature measurement by clock noise or by the thermal diode being located away from the hot spot. to achieve the specified accuracy on this channel, these offsets must be removed. the offset value is stored as a 10-bit, twos complement value in registers 0x11 (high byte) and 0x12 (low byte, left justified). only the upper 2 bits of register 0x12 are used. the msb of register 0x11 is the sign bit. the minimum offset that can be programmed is ?128c, and the maximum is +127.75c. the value in the offset register is added or subtracted to the measured value of the remote temperature. the offset register powers up with a default value of 0c and will have no effect unless the user writes a different value to it. table 10. sample offset register codes offset value 0x11 0x12 ?128c 1000 0000 00 00 0000 ?4c 1111 1100 00 00 0000 ?1c 1111 1111 00 000000 ?0.25c 1111 1111 10 00 0000 0c 0000 0000 00 00 0000 +0.25c 0000 0000 01 00 0000 +1c 0000 0001 00 00 0000 +4c 0000 0100 00 00 0000 +127.75c 0111 1111 11 00 0000 one-shot register the one-shot register is used to initiate a conversion and comparison cycle when the ADT7461 is in standby mode, after which the device returns to standby. writing to the one-shot register address (0x0f) causes the ADT7461 to perform a conversion and comparison on both the internal and the external temperature channels. this is not a data register as such, and it is the write operation to address 0x0f that causes the one-shot conversion. the data written to this address is irrelevant and is not stored. consecutive alert register the value written to this register determines how many out-of- limit measurements must occur before an alert is generated. the default value is that one out-of-limit measurement gen- erates an alert . the maximum value that can be chosen is 4. the purpose of this register is to allow the user to perform some filtering of the output. this is particularly useful at the fastest three conversion rates, where no averaging takes place. this register is at address 0x22. table 11. consecutive alert register bit register value number of out-of-limit measurements required yxxx 000x 1 yxxx 001x 2 yxxx 011x 3 yxxx 111x 4 x = dont care bit. y = smbus timeout bit. default = 0. see serial bus interface section. table 12. list of registers read address (hex) write address (hex) name power-on default not applicable not applicable address pointer undefined 00 not applicable local temperature value 0000 0000 (0x00) 01 not applicable external tempera ture value high byte 0000 0000 (0x00) 02 not applicable status undefined 03 09 configuration 0000 0000 (0x00) 04 0a conversion rate 0000 1000 (0x08) 05 0b local temperature high limit 0101 0101 (0x55) (85c) 06 0c local temperature low limit 0000 0000 (0x00) (0c) 07 0d external temperature high l imit high byte 0101 0101 (0x55) (85c) 08 0e external temperature low l imit high byte 0000 0000 (0x00) (0c) not applicable 0f one-shot 10 not applicable external te mperature value low byte 0000 0000 11 11 external temperature offset high byte 0000 0000 12 12 external temperatur e offset low byte 0000 0000 13 13 external temperature high limit low byte 0000 0000 14 14 external temperature low limit low byte 0000 0000 19 19 external therm limit 0110 1100 (0x55) (85c) 20 20 local therm limit 0101 0101 (0x55) (85c) 21 21 therm hysteresis 0000 1010 (0x0a) (10c) 22 22 consecutive alert 0000 0001 (0x01) fe not applicable manufacturer id 0100 0001 (0x41) ff not applicable die revision code 0101 0001 (0x51) *writing to address 0f causes the ADT7461 to perform a single measur ement. it is not a data regist er as such and it does not ma tter what data is written to it.
ADT7461 rev. a | page 14 of 24 serial bus interface control of the ADT7461 is carried out via the serial bus. the ADT7461 is connected to this bus as a slave device, under the control of a master device. after a conversion sequence completes, there should be no smbus transactions to the adt7361 for at least one conversion time, to allow the next conversi on to complete. the conversion time depends on the value programmed in the conversion rate register. the ADT7461 has an smbus timeout feature. when this is enabled, the smbus will timeout after typically 25 ms of no activity. however, this feature is not enabled by default. bit 7 of the consecutive alert register (address = 0x22) should be set to enable it. consult the smbus 1.1 specification for more information (www.smbus.org). addressing the device in general, every smbus device has a 7-bit device address, except for some devices that have extended 10-bit addresses. when the master device sends a device address over the bus, the slave device with that address will respond. the ADT7461 is available with one device address, 0x4c (1001 100b). the serial bus protocol operates as follows: 1. the master initiates data transfer by establishing a start condition, defined as a high-to-low transition on the serial data line sdata, while the serial clock line sclk remains high. this indicates that an address/data stream will follow. all slave peripherals connected to the serial bus respond to the start condition and shift in the next eight bits, consis- ting of a 7-bit address (msb first) plus an r/ w bit, which determines the direction of the data transfer, i.e., whether data will be written to or read from the slave device. the peripheral whose address corresponds to the transmitted address responds by pulling the data line low during the low period before the ninth clock pulse, known as the acknowledge bit. all other devices on the bus now remain idle while the selected device waits for data to be read from or written to it. if the r/ w bit is a 0, the master will write to the slave device. if the r/ w bit is a 1, the master will read from the slave device. 2. data is sent over the serial bus in a sequence of nine clock pulses, eight bits of data followed by an acknowledge bit from the slave device. transitions on the data line must occur during the low period of the clock signal and remain stable during the high period, since a low-to-high transition when the clock is high may be interpreted as a stop signal. the number of data bytes that can be transmitted over the serial bus in a single read or write operation is limited only by what the master and slave devices can handle. 3. when all data bytes have been read or written, stop con- ditions are established. in write mode, the master will pull the data line high during the tenth clock pulse to assert a stop condition. in read mode, the master device will override the acknowledge bit by pulling the data line high during the low period before the ninth clock pulse. this is known as no acknowledge. the master will then take the data line low during the low period before the tenth clock pulse, then high during the tenth clock pulse to assert a stop condition. any number of bytes of data may be transferred over the serial bus in one operation, but it is not possible to mix read and write in one operation because the type of operation is determined at the beginning and cannot subsequently be changed without starting a new operation. in the case of the ADT7461, write operations contain either one or two bytes, while read opera- tions contain one byte. to write data to one of the device data registers or to read data from it, the address pointer register must be set so that the cor- rect data register is addressed. the first byte of a write operation always contains a valid address that is stored in the address pointer register. if data is to be written to the device, the write operation contains a second data byte that is written to the register selected by the address pointer register. this is illustrated in figure 17. the device address is sent over the bus followed by r/ w set to 0. this is followed by two data bytes. the first data byte is the address of the internal data register to be written to, which is stored in the address pointer register. the second data byte is the data to be written to the internal data register.
ADT7461 rev. a | page 15 of 24 04110-0-003 a6 19 1 a5 a4 a3 a2 a1 a0 r/w d7 d6 d5 d4 d3 d2 d1 d0 sclk sdat 9 a start by master ack. by ADT7461 frame 1 serial bus address byte frame 2 address pointer register byte frame 3 data byte sclk (continued) sdata (continued) ack. by ADT7461 ack. by ADT7461 stop by master 9 1 d7 d6 d5 d4 d3 d2 d1 d0 f i gur e 1 7 . w r i t i n g a regi ster a ddr ess t o the a ddr ess p o i n t e r re gi st er , th en w r i t i n g d a ta t o the s e l ect e d re gi st er 04110-0-004 sclk s data start by master ack. by ADT7461 ack. by ADT7461 stop by master frame 1 serial bus address byte frame 2 address pointer register byte 19 1 a6 a5 a4 a3 a2 a1 a0 r/w d7 d6 d5 d4 d3 d2 d1 d0 9 f i g u re 18. w r it ing t o t h e addres s p o int e r r e g i s t er o n ly 04110-0-005 sclk s dat a start by master ack. by ADT7461 frame 1 serial bus address byte frame 2 data byte from ADT7461 nack. by master stop by master 19 1 9 a6 a5 a4 a3 a2 a1 a0 r/w d7 d6 d5 d4 d3 d2 d1 d0 f i g u re 19. r e ad ing f r o m a p r ev i o us ly s e le c t ed r e g i s t e r w h en r e adin g da t a f r o m a r e g i s t er t h er e a r e two p o s s i b i l i t ies. 1. i f th e ADT7461 s addr es s p o in t e r r e g i s t er val u e is unkn own o r n o t t h e desire d va l u e, i t is n e cess a r y to s e t i t to t h e co r - r e c t va l u e b e fo re d a t a can b e r e ad f r o m t h e des i r e d da t a r e g i s t er . this is do ne b y wr i t in g t o th e adt746 1 as bef o r e , b u t o n l y t h e da t a b y t e con t a i ning t h e r e g i st er r e ad addr es s is s e n t , si n c e d a t a is n o t t o b e wr i t t e n t o t h e r e g i st er . this is s h own in f i gur e 18. a r e ad o p er a t ion is t h en p e r f o r m e d co n s ist i n g o f t h e s e r i a l b u s addr es s, r / w bi t s e t t o 1 , f o l l ow e d by t h e d a t a by t e re a d f r o m th e da ta r e g i s t er . this is sho w n in f i gur e 1 9 . 2. i f t h e addr es s p o in t e r r e g i st er is kn o w n t o b e a t t h e desir e d addr ess, da t a c a n b e r e ad f r o m t h e co r r esp o n d i n g d a t a r e g- ist e r w i t h o u t f i rst wr i t in g t o t h e addr ess p o in ter r e g i st er a nd t h e b u s t r an s a c t io n sh own in f i gur e 18 can b e o m i tte d . n o t e tha t al t h oug h i t is p o s s i b l e t o r e ad a da ta b y t e f r o m a da t a r e g i s t er w i t h o u t f i rs t wr i t i n g t o t h e addr es s p o i n t e r r e g i s t er , if t h e addr es s p o i n t e r r e g i s t er is a l r e ad y a t t h e co r r e c t val u e , i t is n o t p o ssi b le t o wr i t e d a t a t o a reg i st er wi t h o u t wr i t i n g t o t h e addr es s p o in ter r e g i s t er b e c a us e t h e f i rs t da t a b y t e o f a wr i t e is al wa ys wr i t ten to t h e addr es s p o in t e r r e g i st er . a l s o n o t e t h a t s o m e o f t h e r e g i s t ers ha ve dif f er en t addr es s e s for r e ad an d wr i t e o p era t io ns. th e wr i t e addr es s o f a r e g i s t er m u st b e w r it te n to t h e a ddre s s p o i n te r i f da t a i s to b e w r it te n to t h a t r e g i st er , b u t i t ma y n o t b e p o ss i b le t o r e a d da t a f r o m t h a t addr es s. th e r e ad addr es s o f a reg i s t er m u st b e wr i t t e n t o t h e a d d r e s s p o i n t e r b e f o re d a t a c a n b e re a d f r om t h a t re g i s t e r .
ADT7461 rev. a | page 16 of 24 alert output this is a p plicab le w h en pin 6 is co nf igur e d as an aler t output . the aler t o u t p u t g o es l o w wh en ev e r a n o u t- o f - l i m i t m e as ur e - m e n t is de t e c t e d , o r if t h e r e m o t e t e m p er a t ur e s e n s o r is o p en cir c ui t. i t is a n op en-dra in o u t p u t an d r e q u ir es a p u l l -u p t o v dd . se v e r a l aler t o u t p uts ca n b e wir e -ore d to get h er , s o t h a t t h e c o m m on l i ne w i l l go l o w i f one or more of t h e aler t output s go es l o w . the aler t o u t p u t ca n be us e d as an in t e r r u p t sig n al to a p r o- ces s o r , o r i t ma y be us e d as an sm b a l e r t . sla v e de vices on t h e s m b u s ca nn o t n o r m al l y sig n al t o th e b u s master tha t t h e y wan t t o talk , b u t th e sm b a l e r t f u n c tion al lo ws th em t o do s o . on e o r m o r e aler t o u t p uts can b e c o nn e c te d to a c o mm on sm b a l e r t lin e t h a t is conn e c te d t o t h e mas t er . w h en t h e sm b a l e r t lin e is p u l l e d lo w b y o n e o f t h e de vices, t h e f o ll o w i n g p r oc ed u r e oc cu r s ( s ee f i g u r e 2 0 . ) : 04110-0-006 alert response address master sends ara and read command device sends its address rd start ack device address no ack stop master receives smbalert f i g u re 20. u s e of s m b a le rt 1. sm b a l e r t is p u l l ed lo w . 2. m a st er ini t i a t e s a r e ad o p er a t ion an d s e n d s t h e aler t r e s p o n s e addr ess (ara = 0001 100). this is a gen e ral cal l addr ess t h a t m u st n o t b e us e d a s a sp e c if ic de vi ce addr ess. 3. the de v i ce w h o s e aler t output i s l o w re sp ond s to t h e aler t r e s p o n s e addr es s and t h e mas t er r e ads i t s de vice addr ess. a s t h e de vice a ddr ess i s s e ve n b i ts, an ls b o f 1 is adde d . t h e ad d r ess o f t h e d e vi c e is n o w k n o w n a nd i t can be in t e r r oga t e d in t h e us ual wa y . 4. i f m o r e than one de vice s aler t o u t p ut is lo w , t h e on e wi t h t h e lo w e st de vice a ddr ess wi l l h a ve p r io r i t y , in acco r - d a nc e w i t h nor m a l sm bu s ar bit r a t i o n . 5. on ce t h e ad t7 461 has r e s p onded t o t h e aler t r e s p o n s e a d d r e s s , it w i l l re s e t it s aler t output , prov i d e d t h a t t h e e r r o r co n d i t i o n th a t ca use d th e aler t no l o nge r e x i s t s . i f th e sm b a l e r t lin e r e ma ins lo w , th e mast er wil l s e nd the ar a a g ain, and s o o n un t i l a l l de v i ces w h os e aler t out - put s we re l o w h a ve re sp o n d e d. low power standby mode the ad t7461 c a n be p u t in t o lo w p o w e r s t a ndb y m o de b y s e t- t i n g bi t 6 o f t h e co nf igura t io n r e g i st er . w h e n bi t 6 is lo w , t h e ADT7461 o p era t es n o r m al l y . w h en b i t 6 is hig h , th e ad c is in h i b i t e d , an d an y con v ersio n i n p r og r e ss is t e r m ina t e d w i t h o u t wr i t in g t h e r e s u l t t o t h e co r r es p o n d in g val u e r e g i s t er . t h e sm bu s i s st i l l e n abl e d. p o w e r c o nsu m pt i o n i n t h e st a ndb y m o de is r e d u ce d t o les s tha n 10 a if th er e is no s m b u s ac ti vi ty o r 100 a if th er e a r e c l o c k an d da ta sig n als on th e b u s. w h en t h e d e vic e is in st and b y m o d e , i t is st i l l p o ssi b le t o i n i t i a t e a on e - s h o t c o n v e r s i on of b o t h c h an nel s by w r it i n g to t h e on e - s h ot r e g i s t er (a ddr es s 0x0f), a f t e r w h ich t h e de vice wil l r e t u r n to st a n db y . i t do e s not m a t t e r w h a t i s w r i tte n to t h e one - s h ot r e g i s t er , al l da ta wr i t t e n t o i t is ig n o r e d . i t is als o p o s s i b le t o wr i t e ne w val u e s t o t h e li mi t re g i s t er w h i l e in st a n d b y m o de . i f t h e va l u es s t o r e d in t h e t e m p er a t ur e va l u e r e g i s t ers a r e n o w o u tside t h e ne w limi ts, an aler t i s ge ne r a te d, e v e n t h ou g h t h e ADT7461 is s t il l in s t an d b y . sensor fa ult detec t ion a t i t s d+ in p u t, th e ADT7461 c o n t a i n s in t e r n al s e n s o r fa u l t dete c t ion cir c ui t r y . this cir c ui t ca n dete c t s i tua t io n s w h er e an ext e r n al r e m o t e dio d e is e i t h er n o t conn e c t e d or in co r r e c t l y co nnec t e d t o t h e ADT7461. a s i m p le v o l t a g e c o m p a r a t o r tr i p s if t h e v o l t a g e a t d + exce e d s v dd ?1 v (typ ical), sig n if yin g an o p en c i rc u i t b e t w e e n d + an d d ? . t h e output of t h i s c o m p ar ator i s ch e c k e d w h en a co n v ersio n is i n i t ia t e d . bi t 2 o f t h e st a t us r e g i st er (o p e n f l a g ) is s e t if a f a u l t is det e c t e d . i f t h e aler t pi n is ena b le d , s e t t i n g t h is f l a g wi l l ca us e aler t t o as s e r t lo w . i f t h e us er do es n o t wish t o us e a n ext e r n al s e n s o r wi t h t h e ADT7461, th en t o p r ev en t co n t in uo us s e t t in g o f th e o p e n f l ag, t h e us er sh o u ld t i e t h e d+ an d d? in p u ts t o g e t h er . the ADT7461 interrupt system the ad t7461 has tw o in t e r r u p t o u t p u t s, aler t and therm . b o t h ha ve dif f er en t f u n c t i o n s and b e h a vio r . aler t is maskab le a nd r e sp on ds to viol a t io n s o f s o f t wa r e - p r o g r a m m e d te m p er a- tu re l i m i t s or an op e n - c i r c u it f a u l t on t h e e x te r n a l d i o d e. therm is in te nde d as a fa i l -s a f e i n ter r u p t o u tp u t t h a t c a nn ot be ma sk e d . i f t h e ext e r n al or lo cal t e m p era t ur e exce e d s t h e p r og ra mm e d hig h t e m p era t u r e limi ts o r e q u a ls o r exce e d s th e lo w t e m p er a- tu re l i m i t s , t h e aler t output i s a s s e r t e d l o w . a n op e n - c i r c u it fa u l t on t h e ext e r n al dio d e als o ca us es aler t to a s s e r t . aler t is r e s e t w h en s e r v ice d b y a m a st er r e adin g i t s d e v i ce ad dr ess, p r o v ide d t h e er r o r co n d i t ion has g o n e a w a y an d t h e st a t us re g i ste r h a s b e e n re s e t .
ADT7461 rev. a | page 17 of 24 the therm o u t p u t as s e r t s lo w if th e ext e r n al o r lo cal t e m p er - a t ur e exce e d s t h e p r og ra mm e d therm limi ts. therm te m p - era t ur e limi ts sho u ld n o r m al l y b e e q ual t o o r g r e a t e r than the hig h t e m p era t u r e limi ts. therm is r e s e t a u t o ma t i ca l l y w h en th e t e m p e r a t ur e falls ba c k wi th in th e therm limi t. th e ext e r - na l limi t is s e t b y defa u l t t o 85 c, as is t h e lo ca l therm limi t. a h y s t er esis val u e ca n b e p r og ra mm e d ; in w h ich c a s e , therm r e s e ts w h e n t h e t e m p era t ur e fal l s t o t h e li mi t val u e min u s t h e h y st er esis va l u e . this a p plies t o b o t h lo ca l and r e m o t e m e asur e - m e n t chann e ls. the p o w e r - on h y s t er esis defa u l t val u e is 10c, b u t th i s ma y be r e p r ogra m m ed t o a n y val u e a f t e r po w e r - u p . the h y s t er esis lo o p o n t h e therm o u t p u t s is us ef u l w h en therm is us ed f o r o n /of f co n t r o l o f a fa n. th e us er s syst em c a n be se t u p so th a t wh en therm ass e r t s a fa n c a n b e swi t ch e d o n t o co ol th e syst em. w h e n therm go e s h i g h ag ai n , t h e fan c a n b e s w i t ch e d o f f. p r og ra mmin g a h y s t er esis val u e p r o t e c ts f r o m fan ji t t e r , w h er e t h e tem p era t ur e h o v e rs a r o u nd th e therm limi t, and t h e fan is co nst a n t ly b e i n g s w i t ch e d . table 13. therm hyst eresis therm hyster esis binary represe n tation 0c 0 000 0000 1c 0 000 0001 10c 0 000 1010 f i gur e 21 s h o w s h o w the therm and aler t output s op e r a t e. a us er ma y wi sh t o us e t h e aler t o u t p u t as a sm b a l e r t to sig n al t o t h e h o s t v i a t h e s m bu s t h a t t h e t e m p e r a t ur e has r i s e n. the us er co u l d us e t h e therm o u t p u t to t u r n o n a fan to co ol t h e sys t em, if t h e t e m p era t ur e c o n t i n ues t o i n cr e a s e . this m e t h o d w o u l d en s u r e t h a t t h ere is a fa i l -s a f e me cha n ism t o co ol t h e sys t em, wi t h o u t t h e ne e d fo r h o s t i n t e r v en t i o n . 04110-0-007 1 3 2 4 therm limit high temp limit therm limit-hysteresis reset by master alert therm 100 c temperature 90 c 80 c 70 c 60 c 50 c 40 c f i g u re 21. o p er at i o n of t h e aler t and therm i n t e rrupts 1. i f t h e m e as ur e d t e m p era t ur e exce e d s t h e hig h tem p er a t ur e limi t, t h e aler t o u t p u t wil l as s e r t lo w . 2. i f t h e t e m p era t ur e co n t in ues t o in cr e a s e an d exce e d s t h e therm limi t, t h e therm o u t p u t as s e r t s lo w . this can b e us ed t o thr o t t le th e cp u c l o c k o r swi t c h on a f a n. 3. the therm o u t p u t de as s e r t s (g o e s hig h ) w h en t h e t e m p era t ur e fal l s t o therm limi t mi n u s h y ster esis. i n f i gur e 21, t h e defa u l t h y s t er esis val u e o f 10c is s h o w n. 4. the aler t o u t p u t de as s e r t s o n l y w h e n t h e t e m p er a t u r e has fal l en b e lo w t h e hig h tem p e r a t ur e limi t, and t h e mas t er has r e ad t h e d e v i ce addr ess an d cle a r e d t h e st a t us r e g i ster . p i n 6 o n t h e ADT7461 can be c o nf igur ed as ei th er an aler t output or a s an a d d i t i on a l therm output . therm2 wi l l ass e r t lo w w h e n t h e t e m p er a t ur e exce e d s t h e p r og ra mme d lo cal a nd/o r r e m o t e hig h t e m p era t u r e limi ts. i t is r e s e t in t h e s a m e ma n n er as therm , a n d i t is n o t ma skab le. t h e p r o g ra mme d h y s t er esis val u e a p plies t o therm2 also . f i gur e 22 s h o w s h o w therm and therm2 mig h t o p era t e t o g e t h er t o i m plem e n t tw o m e t h o d s o f co olin g t h e sys t em. i n th i s e x a m p l e , th e therm2 limi ts a r e s e t l o w e r t h a n t h e therm limi ts. the therm2 output c o u l d b e u s e d to t u r n on a fa n. i f t h e t e m p era t ur e co n t in ues t o r i s e a n d e x ce e d s t h e therm limi ts, t h e therm output c o u l d prov i d e a d d i t i on a l coo l i n g b y th r o t t li n g th e c p u . therm2 limit therm limit 04110-0-008 therm2 1 3 2 4 temperature therm 90 c 80 c 70 c 60 c 50 c 40 c 30 c f i g u re 22. o p er at i o n of t h e therm and therm2 i n t e rrupts 1. w h en t h e therm2 l i m i t i s e x ceed ed , th e therm2 sig n al ass e r t s lo w . 2. i f t h e t e m p era t ur e co n t in ues t o in cr e a s e an d exce e d s t h e therm limi t, t h e therm output a s s e r t s l o w . 3. the therm o u t p u t de as s e r t s (g o e s hig h ) w h en t h e t e m p era t ur e fal l s t o therm limi t mi n u s h y ster esis. i n f i gur e 22, t h er e is n o h y s t er esis val u e sh o w n. 4. a s t h e sys t em c o ols f u r t h e r , a n d t h e t e m p er a t u r e fal l s be lo w t h e therm2 limi t, th e therm2 sig n al r e s e ts. a g a i n, n o h y st e r esis val u e is s h o w n fo r therm2 . b o t h t h e ext e r n al a nd i n t e r n al tem p er a t ur e m e as ur emen t s w i l l ca us e therm a nd therm2 t o o p era t e as des c r i b e d .
ADT7461 rev. a | page 18 of 24 applic ati o n informa t io n noise filtering f o r t e m p e r a t ur e sen s o r s o p e r a t in g in n o is y en vir o nm en ts , t h e ind u st r y st anda rd p r ac t i c e was to p l ac e a c a p a c i to r ac r o ss t h e d+ and d? p i n s t o hel p com b a t t h e ef fe c t s o f no is e . h o we ver , la rge c a p a c i t a n c es a f fe c t t h e acc u rac y o f t h e t e m p er a t ur e me as ure m e n t, l e ad in g t o a r e c o mm en ded m a xim u m ca p a ci t o r v a l u e o f 1, 0 0 0 pf . w h ile t h i s ca pa ci t o r wil l r e d u ce t h e n o ise , i t wil l n o t e l im ina t e i t , mak i n g i t dif f i c u l t t o us e t h e s e n s o r i n a ver y no isy e n v i r o nme n t. the ad t7461 has a ma jo r adva n t a g e o v er o t her de vices w h en i t co m e s t o e l imi n a t in g t h e ef fe c t s o f n o is e o n t h e ext e r n al s e n s o r . the s e r i es r e sis t a n c e can c e l l a t i on fe a t ur e al lo ws a f i l t er t o b e co n s t r uc t e d b e t w e e n t h e ext e r n al t e m p era t ur e s e n s o r an d t h e p a r t . th e ef fe c t o f a n y f i l t er r e s i s t a n ce s e en in s e r i e s wi t h t h e r e m o t e s e n s o r is a u t o ma tical l y ca n c e lled f r o m th e t e m p e r a t ur e r e s u l t . t h e co n s tr ucti o n o f a f i l t e r allo w s th e ad t 7461 a n d t h e r e m o t e t e m p era t ur e s e ns o r t o o p era t e i n n o isy en vir o nm e n ts. f i gur e 2 3 s h o w s a lo w-p a ss r - c - r f i l t er , w i t h t h e fol l o w ing val u es: r = 100 ? a nd c = 1 nf . this f i l t er in g r e d u ces bo th comm o n - m o de n o is e and dif f er en t i al n o i s e . 04110-0-009 d+ 1nf 100 ? remote t emperature sensor d? 100 ? f i g u re 23. f i lte r b e t w een r e m o te s e ns or and a d t7 4 61 f a ct or s a ffe cti n g d i o d e a c c u r a c y remote sensi n g diode the ad t7461 is desig n e d t o wo rk wi th s u bstra t e tra n sis t o r s b u il t in t o p r oces so r s o r w i t h d i scr e t e tra n si s t o r s. s u b s tra t e tra n - sis t o r s wil l g e n e ral l y be p n p ty p e s wi th t h e col l e c t o r co nne c t e d t o th e su bs tr a t e . dis c r e t e typ e s ca n be ei t h er pnp o r npn tran- sisto r co nne c t e d as a dio d e (b a s e sh o r te d to co l l e c to r ) . i f a n npn t r a n sisto r is us e d , t h e col l e c to r a nd b a s e ar e co nne c t e d to d+ a nd t h e emi t t e r t o d?. i f a p n p t r a n sist o r is us e d , t h e col- le c t o r a nd b a s e a r e co n n e c te d to d? a nd t h e e m i t ter to d+. t o r e d u ce t h e er r o r d u e t o va r i a t io n s in b o t h s u b s t r a t e an d dis c r e t e tra n sisto r s, a s e v e ral fac t o r s s h o u ld b e t a k e n in t o co n s idera t ion: ? the ide a l i ty fac t o r , n f , of t h e t r ans i stor i s a me a s u r e of t h e d e vi a t i o n o f th e th e r m a l d i o d e f r o m i d eal be ha vi o r . t h e ADT7461 is tr immed f o r a n n f val u e o f 1.008. the f o l l o w - in g e q ua t i on ma y b e us e d t o c a lc u l a t e t h e er r o r in t r o d uc e d a t a t e m p era t ure t (c), w h e n usin g a t r a n sis t o r w h os e n f do es n o t eq ual 1.008. c o n s u l t th e p r o c es s o r da ta sh eet f o r th e n f val u es. ? t = ( n f ? 1.00 8)/1.008 (273.15 k e lvin + t) t o fa ct o r th i s in, th e use r ca n wri t e th e ? t val u e t o t h e o f fs et r e g i s t er . i t wi l l t h en b e a u to ma t i c a l l y adde d t o o r s u b t rac t e d f r o m t h e t e m p era t ur e m e as ur e m en t b y th e ADT7461. ? s o me cp u man u fac t ur ers sp e c i f y t h e hig h and lo w c u rr en t le v e l s o f t h e s u b s t r a t e t r an sis t o r s. th e hig h c u r r en t le ve l o f th e ADT7461, i hi g h , is 96 a a nd the lo w le v e l c u r r en t, i lo w , is 6 a. i f th e ad t7461 c u r r en t lev e l s do n o t ma t c h the c u r r en t le v e l s sp e c if ie d b y t h e cpu man u fac t ur er , i t ma y become neces s ar y t o r e m o v e a n o f fs et. th e cp u s da ta s h e e t wi l l advis e w h et h e r t h is of fs et n e e d s t o b e r e m o v e d a nd h o w to ca lc u l a t e i t . this o f fs et ma y b e p r o g ra mme d to t h e o f fs et r e g i s t er . i t is im p o r t an t t o n o t e t h a t if m o r e t h a n o n e o f fs et m u st b e con s ider e d , t h e alg e b r a i c s u m o f t h es e o f fs ets m u s t b e p r og ra mm e d t o t h e o f fs et r e g i s t er . i f a dis c r e t e tran sis t o r is bein g us ed wi t h the ad t7461, t h e best acc u rac y wil l b e ob ta ined b y cho o sin g de vices acco r d in g t o t h e fol l o w ing c r i t er i a : ? b a s e -emi t t er v o l t a g e g r ea t e r than 0.25 v a t 6 a, a t the hig h e s t o p er a t in g t e m p era t ur e . ? b a s e -emi t t er v o l t a g e les s than 0 . 95 v a t 100 a, a t t h e lo w e s t o p era t ing t e m p era t ur e . ? b a s e r e sis t an c e les s tha n 100 ?. ? sma l l va r i a t io n in h fe (50 t o 150 ) tha t in dica t e s t i g h t co n t r o l o f v be char ac ter i st ic s . t r a n sis t o r s, s u ch as t h e 2 n 3904 , 2n3906, o r eq ui valen t s in s o t - 2 3 p a ck ag e s are su i t a b l e d e v i c e s to u s e. thermal inertia and self-heating a c c u rac y dep e nds o n t h e t e m p e r a t ur e o f t h e r e m o te s e n s in g dio d e and/o r t h e in ter n al t e m p era t ur e s e n s o r b e in g a t t h e s a m e t e m p era t ur e as t h a t b e in g m e asur e d . m a n y fac t o r s ca n a f fe c t th i s . i d eall y , th e se n s o r sh o u ld b e i n g o o d t h e r m a l co n t a c t wi th t h e p a r t o f t h e s y s t em b e ing m e as ur e d . i f i t is no t, t h e t h er mal in er t i a c a us e d b y t h e s e ns o r s mas s c a us es a l a g in t h e r e s p on s e o f t h e s e ns o r t o a t e m p era t ur e cha n g e . i n t h e cas e o f t h e r e m o te s e ns or , t h i s s h o u l d not b e a pro b l e m s i nc e i t w i l l b e e i t h e r a s u bs tr a t e tran sist o r in t h e p r o c e s s o r o r a smal l p a c k a g e de vic e , s u c h as t h e sot - 23, p l ace d in c l os e p r o x imi t y to i t . t h e on - c h i p s e ns or , howe ve r , i s of te n re mote f r om t h e pro c e s s o r a nd o n ly m o ni to rs t h e ge n e ra l a m b i e n t tem p era t ur e a r o u nd t h e p a cka g e . the t h er mal t i m e co n s t a n t o f t h e so ic-8 p a cka g e i n s t il l a i r is abo u t 140 s e co nds, and if th e am b i en t a i r t e m p era t ur e q u ic kl y c h an g e d b y 100 deg r ees, i t w o u l d ta k e a b o u t 12 min u tes (5 tim e con s t a n t s) f o r th e j u n c tio n t e m p er a t ur e o f th e ad t7461 t o s e t t le wi t h in 1 deg r ee o f this. i n p r ac tice , t h e ADT7461 p a c k - a g e is i n e l e c t r ic al , a nd h e n c e t h er mal , co n t ac t wi t h a p c b and m a y also be in a f o r c ed a i rf lo w . h o w a c cura t e l y th e t e m p era t ur e o f t h e b o a r d and/o r t h e fo r c e d a i r f lo w r e f l e c ts th e tem p era t ur e t o b e m e as ur e d als o a f fe c t s t h e acc u rac y . s e lf-he a t i ng d u e t o t h e p o we r d i ss ip ate d i n t h e a d t 7 4 6 1 or t h e re mot e s e ns or c a u s e s t h e chi p t e m p er a t ur e o f t h e de v i ce o r r e m o te s e n s o r t o r i s e a b o v e am b i en t. h o w e v e r , t h e c u r r en t fo r c e d t h r o ug h t h e r e m o te
ADT7461 rev. a | page 19 of 24 se n s o r i s so s m all th a t se l f - h ea t i n g i s n e gl i g i b l e . i n t h e ca se o f th e ADT7461, th e w o rst-c a s e c o n d i t ion o c c u rs when t h e de vic e is co n v er t i n g a t 64 co n v ersio n s p e r s e con d w h i l e sinking t h e max i m u m c u r r en t o f 1 m a a t t h e aler t a nd therm output . i n th i s ca se , t h e t o tal po w e r d i s s i p a t i o n in th e devi ce i s a b o u t 4.5 mw . th e t h er mal r e sis t a n ce, ja , o f t h e so i c -8 p a cka g e is a b o u t 121 c/ w . layout co nsidera t io ns dig i t a l b o a r ds c a n b e ele c t r ica l ly n o isy en v i r o n m e n ts, and t h e ADT7461 is me as ur in g v e r y smal l v o l t a g es f r o m the r e m o t e s e n s o r , s o ca r e m u st b e t a k e n to minim i z e n o i s e i n d u ce d a t t h e s e ns or i n put s . t h e f o l l ow i n g pr e c aut i ons s h ou l d b e t a ke n : 1. p l ace t h e adt7 461 as c l os e as p o s s i b le t o t h e rem o t e s e n s in g dio d e . pr o v ide d t h a t t h e w o rst n o is e s o u r ces, i . e . , clo c k gener a to r s , da t a / a ddr ess b u s e s, a nd cr t s a r e a v o i de d , this dis t an c e can b e 4 in ch es t o 8 in ch es. 2. r o u t e th e d + a n d d C tra c k s c l ose t o g e th e r , i n pa ralle l , w i t h g r o u n d e d gua r d t r acks o n e a ch side. t o mi nim i ze ind u c t an ce an d r e d u ce n o is e p i ck-u p , a 5 mi l t r a c k w i d t h a nd sp aci n g is r e co m m e n de d . pr o v ide a g r o u nd plan e un der t h e tracks if p o s s i b le . 04110-0-010 5mil 5mil 5mil 5mil 5mil 5mil 5mil gnd d+ d? gnd f i g u re 24. t y pic a l a r r a ng e m ent of sig n al t r ack s 3. t r y t o minimize t h e n u m b er o f co p p er/s older j o in ts t h a t c a n ca us e t h er mo co u p le ef fe c t s. w h er e cop p er/s older jo i n ts a r e used , m a k e s u r e th a t th ey a r e i n bo t h th e d + a n d d ? pa th a n d a t th e sa m e t e m p era t ur e . ther m o co u p le ef f e c t s s h o u ld no t be a ma jo r p r ob lem as 1c co r r es p o n d s t o a b o u t 200 mv , and ther mo co u p le v o l t a g es a r e ab ou t 3 mv /c o f tem p er a t ur e dif f er en ce . u n les s t h er e a r e tw o t h er m o co uples wi t h a b i g tem p er a t ur e dif f er en t i al b e t w e e n t h e m , t h er m o cou p le v o l t ag es s h o u ld be m u c h les s tha n 200 mv . 4. p l ace a 0.1 f b y p a s s ca p a c i t o r c l os e t o th e v dd pi n . in ext r em e l y n o isy en vir o nm e n ts, a n i n p u t f i l t er c a p a ci t o r ma y b e p l ace d acr o s s d+ a nd d? c l os e t o th e ad t7461. this c a p a ci t a n c e can ef fe c t t h e t e m p era t ur e m e as ur emen t, s o c a re m u st b e t a k e n to e n su re t h a t an y c a p a c i t a nc e s e e n a t d+ and d? is a maxim u m o f 1,000 pf . this maxim u m val u e i n cl udes t h e f i l t er ca p a c i t a n c e , pl us a n y c a b l e o r s t ra y ca p a c i t a n c e b e t w e e n t h e pin s and t h e s e n s o r di o d e. 5. i f th e dis t an ce to th e r e m o t e s e n s o r is m o r e than 8 in ch es, t h e us e o f t w ist e d p a ir ca b l e is r e co m m e n de d . t h is wi l l w o rk u p t o abou t 6 f e et t o 12 f e et. f o r r e al l y lo n g dis t an ces (u p t o 100 f e et), us e a s h ie lde d twis t e d p a ir , s u ch as t h e b e lden n o . 8451 micr o p h o n e ca b l e. c o n n e c t t h e t w iste d p a ir to d+ a nd d? and t h e s h ie ld t o gnd clos e t o th e ADT7461. l e a v e t h e r e m o t e en d o f t h e shi e ld u n co nne c t e d to a v o i d g r o u nd lo ops. b e ca us e t h e m e as ur emen t t e chniq u e us es s w i t ch e d c u r r en t s o ur ces, exces s i v e ca b l e o r f i l t er ca p a ci t a n c e can a f fe c t t h e m e as ur e m en t. w h en usin g lo ng ca b l es, t h e f i l t er ca p a ci t a n c e m a y b e re d u c e d or re move d.
ADT7461 rev. a | page 20 of 24 applic ati o n circuit f i gur e 25 s h o w s a typ i cal a p p l ic a t io n c i r c ui t f o r th e ADT7461 usin g a dis c r e te s e n s o r t r a n sistor co nn e c te d v i a a shi e lde d , t w iste d p a ir cable. th e p u l l -u ps o n scl k , s d a t a, a nd aler t a r e r e q u ir e d o n ly if t h e y a r e n o t a l r e ad y p r o v ide d e l s e w h er e i n th e sys t e m . the scl k an d s d a t a p i n s o f th e ADT7461 c a n be in t e r f ace d dir e c t l y t o th e s m b u s o f a n i/o co n t r o l l er , s u c h as th e i n t e l 820 chi p s e t. 04110-0-011 shield 2n3906 or cpu thermal diode al e r t / t h er m2 gnd t h er m d+ d? ADT7461 sclk sdata v dd v dd 3v to 3.6v typ 10k ? typ 10k ? 0.1 f fan control circuit fan enable smbus controller 5v or 12v f i gure 25. t y pic a l a p plic at ion cir c u i t
ADT7461 rev. a | page 21 of 24 outline dimensions 0.25 (0.0098) 0.17 (0.0067) 1.27 (0.0500) 0.40 (0.0157) 0.50 (0.0196) 0.25 (0.0099) 45 8 0 1.75 (0.0688) 1.35 (0.0532) seating plane 0.25 (0.0098) 0.10 (0.0040) 4 1 85 5. 00 ( 0 . 1 9 68) 4. 80 ( 0 . 1 8 90) 4.00 (0.1574) 3.80 (0.1497) 1.27 (0.0500) bsc 6.20 (0.2440) 5.80 (0.2284) 0.51 (0.0201) 0.31 (0.0122) coplanarity 0.10 controlling dimensions are in millimeters; inch dimensions (in parentheses) are rounded-off millimeter equivalents for reference only and are not appropriate for use in design compliant to jedec standards ms-012aa f i g u re 26. 8-l e ad s t anda r d s m a l l o u t l ine p a ckag e [soic ] (r -8) d i mensions sh o w n in m i ll im e t e r s a n d (inc he s) 0.80 0.60 0.40 8 0 4 85 4.90 bsc pin 1 0.65 bsc 3.00 bsc seating plane 0.15 0.00 0.38 0.22 1.10 max 3.00 bsc coplanarity 0.10 0.23 0.08 compliant to jedec standards mo-187aa f i g u re 27. 8-l e ad m i cro s m al l o u t l in e p a ckag e [m s o p ] (rm-8) di me nsio ns sho w n i n m i ll im e t e r s ordering guide mo del temperature r a nge package descri ptio n package o p tio n b r anding smb u s addr es s ADT7461ar ?40c to +125c 8-lead soic r-8 4c ADT7461ar- ree l ?40c to +125c 8-lead soic r-8 4c ADT7461ar- ree l 7 ?40c to +125c 8-lead soic r-8 4c ADT7461arm ?40c to +125c 8-lead msop rm-8 t1b 4c ADT7461ar m -r eel ?40c to +125 c 8-lead msop rm-8 t1b 4c ADT7461ar m -r eel7 ?40c to +125 c 8-lead msop rm-8 t1b 4c ADT7461arz 1 ?40c to +125c 8-lead soic r-8 4c ADT7461arz-reel 1 ?40c to +125c 8-lead soic r-8 4c ADT7461ar z -r eel7 1 ?40c to +125c 8-lead soic r-8 4c ADT7461armz 1 ?40c to +125c 8-lead msop rm-8 t1b 4c ADT7461armz- reel 1 ?40c to +125c 8-lead msop rm-8 t1b 4c ADT7461ar m z- reel7 1 ?40c to +125c 8-lead msop rm-8 t1b 4c eval-ad t7461e b evaluation boar d 1 z = pb-free part.
ADT7461 rev. a | page 22 of 24 notes
ADT7461 rev. a | page 23 of 24 notes
ADT7461 rev. a | page 24 of 24 notes ? 2004 analo g de vices, inc. all rights reserve d . tra d em arks and registered tra d ema r ks are the prop erty of their respective owners . c04110-0-10/04(a)

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