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1c temperature monitor with series resistance cancellation ADT7461* 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 e r compatible with adm1 032 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 2 overte mperature fai l - s afe 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 produc t d e scripti o n the ad t7461 is a d u al-c hann el dig i ta l th er m o m e t e r an 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 th er mal ma na gem e n t syst em s. i t is p i n and r e g i s t er co m p a t ib le 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: s e r i es r e sis t a n ce can c e l l a t i on, w h er 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; c o nf igura b le aler t o u t p u t ; an d an ext e n d e 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 m e as ur e th e t e m p era t ur e o f a r e m o t e t h er - ma l dio d e acc u ra t e t o 1c, an d t h e am b i e n t te m p er a t ur e acc u - ra t e t o 3c. the t e m p era t ur e m e as ur e m en 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 ad m1032, b u t ca n be swi t ched t o a wider m e asur em en t ra n g e , f r o m ?55c t o +150c. the ADT7461 co mm unic a t es o v er a 2-wir e s e r i al in t e r f ace com p a t i - b l e wi th sys t e m 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 o u t p u t sig n als w h en t h e on-chi p o r r e m o te t e m p er a t ur e i s out of r a nge. t h e therm output i s a c o m p ar ator output t h at al lo ws o n /o f f co n t r o l o f a co oling fa n. th e aler t output c a n b e r e co nf igur e d as a s e cond therm o u t p u t if r e q u ir e d . * p rote c t e d b y u . s . p a te n t s 5,195,827; 5,867,012; 5,982,221; 6,097,239; 6,133,753; 6,169,442; o t h e r p a ten t s p e n d ing. 04110- 0- 012 digital mux digital 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 comparator 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 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 ? 2003 analog de vices, i n c. al l r i ght s r e ser v ed . rev. 0
ADT7461 table of contents ADT7461?s p ec if ica t ion s ................................................................. 3 s m b u s t i min g s p e c if ic a t io n s ......................................................... 4 a b s o l u t e m a xim u m r a t i n g s ............................................................ 5 ther mal c h a r ac t e r i s t ics .............................................................. 5 p i n c o nf igura t io n an d pin f u nc t i o n d e s c r i p t ion s ...................... 6 t y p i cal p e r f o r ma n c e c h a r ac t e r i s t ics ............................................. 7 f u n c t i o n al d e s c r i p t io n .................................................................... 9 s e r i es resis t an c e c a n c e l l a t i on .................................................... 9 t e m p er a t ur e m e as ur emen t m e t h o d .......................................... 9 t e m p er a t ur e m e as ur emen t re su l t s .......................................... 10 t e m p er a t ur e m e as ur emen t r a ng e ........................................... 10 t e m p er a t ur e d a t a f o r m a t ......................................................... 10 ADT7461 r e g i st ers .................................................................... 11 s e r i al b u s i n t e r f ace ..................................................................... 14 a ddr es sin g t h e d e vice ............................................................... 14 ale r t o u t p u t ................................................................................ 16 l o w p o w e r s t a n d b y m o de ......................................................... 16 s e n s o r f a u l t d e t e c t io n .............................................................. 16 the ad t7461 i n t e r r u p t s y s t em ............................................... 17 a p plica t ion i n fo r m a t io n ........................................................... 18 f a c t o r s af fe c t in g dio d e a c c u rac y ........................................... 18 ther mal i n er t i a a nd s e lf-h e a t i n g ............................................ 19 l a yo u t c o n s ide r a t io n s ............................................................... 19 a p plica t ion c i r c ui t ..................................................................... 20 o u t l in e dim e n s io n s ....................................................................... 21 or der i n g g u ide . ......................................................................... 21 revisi on h i s t or y rev i s i o n 0: i n i t ial v e r s i o n rev. 0 | page 2 of 2 4
ADT7461 ADT7461?specifications table 1. adt7 461 spec ifications at t a = ?40 c to +1 20c , v dd = 3 v to 5. 5 v, unless oth e rwise noted. parameter min typ max nit test condition s poer sppl supply voltage, v dd 3.0 3.30 5.5 v average operati ng supply current, dd 170 215 a 0.0625 conversi onss e c rate 1 5.5 10 a standby mode , 40c t a +85c 5.5 20 a standby mode, +85c t a +120c ndervoltage locout thresh old 2.2 2.55 2.8 v v dd nput, disables adc, rising edge poweronre set t h reshold 1 2.5 v tempe r at r e todtal cover t er 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 3 6 a m i d d l e level 3 6 a l o w level 3 conversi on tim e 32.13 114.6 ms from stop bit to conversi on co mplete (both ch annel s ) one shot mode with averaging switched on 3.2 12.56 ms oneshot mode with averaging o ff (i.e., conversion rate = 16, 32, or 64 conver sions per second) m a ximum series resistance c a n c elled 3 resistance sp lit evenly on both t h e d+ and d nputs opedra d tal otpts ( ther m , alert ther m2 ) output low voltage, v ol 0.4 v o t = ?6.0 ma 3 high level output leaage curr ent, oh 0.1 1 a v o t = v dd 3 alert output low sin current 1 ma alert forced to 0.4 v smbus te rfa c e 3, 4 logic nput hig h voltage, v h 2.1 v 3 v v dd 3.6 v scl, sdata logic nput low voltage, v l 0.8 v 3 v v dd 3.6 v scl, sdata hysteresis 500 mv smbus output l o w sin current 6 ma sdata forced to 0.6 v logic nput curr ent, h , l ?1 +1 a smbus nput ca pacitance , scl, sdata 5 pf smbus cloc fre uency 400 h smbus timeout 5 25 64 ms ser programm able. scl falling edge to sdata valid time 1 s master clocing in data 1 se e tabl e 8 for in fo rmat ion on ot h e r c o n v ersion rat e s. 2 uarante e d by characte ri a tio n but no t pro d uctio n te s t ed . 3 uarante e d by d e sign but no t pro d uctio n te s t e d . 4 see sm bus timing specif ications section f o r more inf o rmation. 5 d i s a b le d by de fa ul t . d e t a i ls on h o w t o en a b le i t a r e i n t h e smbu s sect i o n o f t h i s da t a sh e e t . rev. 0 page 3 of 2 4
ADT7461 smbus timing specifications table 2. s m bus timing s p ecifications 1 parameter limit at t min , t ma u n i t d e s c r i p t i o n f sclk 400 khz max t low 4.7 s min clock low period, between 10% points. t high 4 s min clock high period, between 90 % points. t r 1 s max clock/data rise time. t f 300 ns max clock/data fall time. t su ; s t a 4.7 s min start condition setup time. t hd; sta 2 4 s min start condition hold time. t su ; da t 3 250 ns min data setup tim e . t hd; dat 300 s min data hold time. t su ; s t o 4 4 s min stop condition setup time. t bu f 4.7 s min bus free time be tween stop and start conditio ns. 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 rev. 0 | page 4 of 2 4
ADT7461 absolute maximum ratings table 3. adt7 461 absolute maximum ratings* p a r a m e t e r r a t i n g positive supply voltage (v dd ) to d ?0.3 v, +5.5 v d+ ?0.3 v to v dd + 0.3 v d? to d ?0.3 v to +0.6 v scl, sdata, alert ?0.3 v to +5.5 v ther m ?0.3 v to v dd + 0.3 v nput current, s d ata, ther m ?1 ma, +50 ma nput current, d ? 1 ma esd rating, all p i ns (human body model) 2000 v maximum unction temperature (t max) 150c storage temperature range ?65c to +150c r reflow pea temperature 220c lead temperature (soldering 10 sec) 300c *st r es se s a b ove t h o se li st ed un der ab sol u t e ma xi m u m r a t i n gs m a y ca use permanent d amage to the d e vice. this is a s t ress rating onl y functional o p e r atio n o f the device at the s e o r any o the r co nd itio ns a b o v e tho se ind i cate d in the o p eratio nal se ctio n o f this s p ecif ication is not impl i ed . e x pos ure to abs o l u te maximum rating co nd itio ns fo r e x te nd ed period s may aff e ct d e vice rel iabil ity. thermal c h aracterstcs 8l e ad so c p a c a g e a = 121c 8l e ad mso p p a c a g e a = 142c rev. 0 page 5 of 2 4
ADT7461 pin conf iguration and pi n function 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-drai n 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 con f igured 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. req u ires pull-up resistor. 8 sclk logic input, smbus serial cl ock. requires pull-u p resistor. rev. 0 | page 6 of 2 4
ADT7461 typical perf orm ance cha r acte ristics 04110-0-017 60 0 2 04 0 6 08 0 leakage reisitanve (m ?
ADT7461 04110-0-016 60 0 100 200 300 400 500 frequency (mhz) 600 te mp e rature e rror ( c) 0 10 20 30 40 50 60mv 100mv 40mv 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 04110-0-020 40 0 100 200 300 3v 5.5v scl clock frequency (khz) 400 50 150 250 350 i dd ( ? rev. 0 page 8 of 2 4
ADT7461 functional description the ad t7461 is a lo cal and r e m o te t e m p er a t u r e s e n s o r an d o v er/un d er t e m p era t ur e ala r m, wi t h t h e adde d a b i l i t y t o a u t o ma t i cal l y c a n c e l t h e ef fe c t o f 3 k (typ ical ) o f r e sis t a n ce in s e r i es wi t h t h e t e m p era t ur e m o ni t o r i n g dio d e . w h en t h e ADT7461 is o p era t in g n o r m al ly , th e o n -bo a rd ad c o p era t es in a f r ee- r un n i n g m o de . th e a n alog i n p u t m u l t i p lex e r al t e rn a t e l y s e le c t s e i t h er t h e o n -chi p t e m p era t ur e s e n s o r to m e as ur e i t s lo cal t e m p er a t u r e o r t h e r e m o t e t e m p era t ur e s e n s o r . the a d c dig i t i ze s th es e sig n als a nd the r e s u l t s a r e s t o r e d in the lo cal and r e m o t e t e m p era t ur e val u e r e g i sters. the lo cal and r e m o te m e as ur e m en t r e s u l t s a r e c o m p a r e d w i t h t h e co r r es p o n d i n g hig h , lo w , and therm t e m p er a t ur e l i mi t s , store d i n e i g h t o n - c h i p re g i ste r s . o u t - of - l i m it c o m p ar i s ons ge n- era t e f l a g s t h a t ar e s t o r e d i n t h e s t a t us r e g i s t er . a r e s u l t t h a t exce e d s t h e hig h t e m p er a t ur e li mi t, t h e lo w t e m p era t ur e limi t, o r a n ext e r n al dio d e fa u l t wi l l c a us e t h e aler t o u t p u t t o as s e r t l o w . ex ceed i n g therm t e m p era t ur e limi ts c a us es t h e therm o u t p u t t o as s e r t lo w . th e aler t o u t p ut ca n b e r e p r o g r a mme d as a s e cond therm output . the lim i t r e g i sters ca n b e p r o g r a m m e d , a nd t h e de vice con - t r ol le d a nd co nf igur e d , v i a t h e s e r i a l s m bus. t h e co n t e n ts o f an y re g i st e r c a n a l s o b e re a d b a ck v i a t h e sm b u s . c o n t r o l a nd conf igur a t io n f u nc t i o n s co n s ist o f : swi t chi n g t h e de vice b e tw e e n n o r m a l o p er a t i o n an d st and b y m o d e , s e le c t i n g t h e tem p era t ur e m e as ur emen t s c ale , mas k in g o r ena b lin g t h e aler t o u t p u t , s w i t ch in g p i n 6 bet w een aler t and therm2 , a nd s e le c t in g t h e co n v ersion r a te. series resistance c a ncellation p a rasi t i c r e sis t an ce , s e en i n s e r i es wi t h t h e r e mo t e dio d e , t o t h e d+ a nd d in p u ts t o the ad t7 461, is ca us ed b y a va r i ety o f fac t o r s, in cl ud ing pcb t r ack r e sist an ce and t r ack len g t h . thi s s e r i es r e sis t a n ce a p p e a r s as a t e m p er a t ur e o f fs et in t h e r e m o te s e n s o r s t e m p era t ur e m e as ur e m en t. this er r o r typ i cal l y ca us es a 0.5c o f fs et p e r ohm o f p a rasi t i c r e sis t a n ce in s e r i es wi t h t h e re mote d i o d e. the ad t7461 a u t o ma t i cal l y can c e l s o u t the ef f e c t o f this s e r i es r e sis t a n c e o n t h e t e m p era t ur e r e ading, g i vin g a m o r e acc u ra t e r e s u l t , wi th o u t t h e n e ed f o r use r c h a r a c t e ri a ti o n o f th i s r e si s - t a n c e. the ADT7461 is desig n e d t o a u to ma tica l l y c a n c el ty p i cal l y u p t o 3 k? o f r e sis t a n ce . b y usin g a n ad van c ed t e m p era t ur e m e as ur e m en t m e t h o d , t h is is t r a n s p a r en t t o t h e us er . t h i s f e a - t u re a l l o w s re s i s t a n c e s to b e a d d e d to t h e s e ns or p a t h to pro d u c e a f i l t e r , all o w i n g th e pa r t t o b e used in n o i s y en vi r o n m en t s . s e e t h e s e c t io n on f o r m o r e det a i l s. n o is e f i l t er in g n o is e f i l t er in g temperature measurement method a sim p le m e t h o d o f m e as ur in g t e m p era t ur e is to explo i t t h e n e g a t i ve t e m p er a t ur e co ef f i cien t o f a dio d e , m e as ur in g t h e b a s e - e mi t t er v o l t a g e (v be ) of a t r ans i stor , op e r a t e d at c o ns t a n t c u r r en t. u n fo r t una t e l y , t h is t e chniq u e r e q u ir es calib r a t ion t o n u l l o u t t h e ef fe c t o f t h e a b s o l u te val u e o f v be , w h i c h v a r i e s f r o m de vice to de vice. the t e c h niq u e us ed in t h e ADT7461 is t o m e as ur e th e c h a n g e in v be w h e n t h e de vice is op era t e d a t t h r e e dif f er en t c u r r en ts. pr e v io us de vice s ha v e us e d o n ly tw o o p era t i n g c u r r en ts, b u t i t is th e use o f a thi r d curr e n t th a t al lo w s a u t o m a ti c ca n c e lla ti o n o f r e sis t a n ces in s e r i es wi t h t h e exter n al t e m p er a t u r e s e n s o r . f i g u re 1 4 show s t h e i n put s i g n a l c o nd i t i o n i ng u s e d to me a s u r e t h e output of an e x te r n a l te m p e r a t u r e s e ns or . t h i s f i g u re show s t h e ext e r n al s e ns o r as a s u bs t r a t e t r a n sis t o r , b u t i t co u l d e q ual l y b e a dis c r e te t r an sist o r . i f a dis c r e t e t r a n sist o r is us e d , t h e col l e c - t o r w i ll n o t be g r o u n d e d a n d sh o u ld be lin k e d t o th e base . t o p r e v en t g r o u nd n o is e in t e r f er in g wi t h t h e m e asur em en t, t h e more ne g a t i v e t e r m i n a l of t h e s e ns or i s no t re fe re nc e d to g r ou nd but i s bi a s e d a b ove g r ou n d by an i n te r n a l d i o d e a t t h e d i n put . c 1 m a y opt i on a l ly b e a d d e d a s a noi s e f i lte r ( r e c om - m e n d ed maxim u m val u e 1000 pf). h o w e v e r , a bet t er o p tion in n o isy e n vir o n m en ts is to a dd a f i l t er , as des c r i b e d in t h e s e c t ion o n . s e e t h e s e c t io n o n fo r more i n for m a t i o n on c 1 . l a yo u t c o n s idera t ion s to m e a s u r e v be , t h e o p era t in g c u r r en t t h r o ug h t h e s e n s o r is s w itc h e d a m on g t h re e rel a te d c u r r e n t s . show n i n f i g u re 1 4 , n1 i a nd n2 i a r e dif f er en t m u l t i p les o f t h e c u r r en t i. th e c u r r en ts t h r o ug h t h e t e m p er a t u r e dio d e a r e sw i t che d b e tw e e n i a nd n1 i, g i vin g v be1 , an d t h e n b e twe e n i and n2 i, g i v i ng v be2 . the t e m p era t ur e ma y t h en b e calc u l a t e d usin g t h e tw o v be m e asur e m en ts. t h is m e t h o d can a l s o b e sh o w n to cancel t h e ef fe c t o f a n y s e ries r e sis t a n ce o n t h e t e m p era t ur e m e as ur em en t. the r e su l t in g v be wa vefo r m s a r e p a ss e d t h r o ug h a 65 k h lo w-p a s s f i l t er to r e m o v e n o is e a nd t h en t o a cho p p e r - s t ab i l i e d a m plif ier . this am plif ies an d r e c t if ies t h e w a v e for m t o p r o d uce a d c vo lt ag e pro p or t i on a l to v be . t h e a d c d i g i ti e s th i s v o l t - a g e and a t e m p e r a t ur e m e as ur em e n t is p r o d uce d . t o r e d u ce t h e ef fe c t s o f n o is e , dig i t a l f i l t er in g is p e r f o r m e d b y a v era g in g t h e r e s u l t s o f 16 m e as ur emen t c y cles fo r l o w co n v ersio n ra t e s. a t ra t e s o f 16, 32, a nd 64 con v ersio n s/s e cond , n o dig i tal a v era g in g tak e s pla c e . sig n al con d i t ionin g and m e as u r em e n t o f t h e in t e r n al t e m p era - t u r e s e n s o r is p e r f o r m e d in t h e s a me ma nn er . rev. 0 page 9 of 2 4
ADT7461 04110-0-002 i n1 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 000 a nd has a r e s o l u t i o n o f 1 c. the ext e r n al t e m p era t ur e val u e is s t o r e d i n tw o r e g i s t ers, wi t h t h e u p p e r b y te in reg i st er 001 a nd t h e lo w e r b y t e in r e g i s t er 010. onl y t h e tw o m s 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 e x t e r n al t e m p er a - t u r e m e as ur em en t a r e s o l u tion o f 0.25c. t s h o w s t h e da t a 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 . a b l e 5 table 5. exte nded te mperature resolution ( r emote tem p erature l o w byte) extended resolution 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. re adin g on e r e g i s t er do es n o t l o ck t h e o t h e r , s o b o t h 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 igur a t ion r e g i st er . a va li d 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 u r e tha t can b e m e as ur ed b y t h e ADT7461 is limi t e d b y the 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 e ra t u r e s e n s ing dio d es ha v e a maxim u m t e m p era t ur e ra n g e o f ?55c t o +150c. 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 , t h e ad t7461 i t s e lf s h o u ld n o t b e expos e d t o t e m p era t ur e s gr ea t e r tha n t h os e s p e c if i e d in t h e a b s o l 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 (de- fa u l t), t h e t e m p era t ur e da t a fo r m a t fo r b o t h in ter n al a nd ext e r - nal t e m p era 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 em e n t ra n g e is in ext e n d e d m o d e , a n o f fs et b i na r y d a t a fo rma t is us e d fo r b o t h in ter n al 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 +64. e x a m ples o f t e m - pe r a t u r e s i n b o th d a ta f o rm a t s a r e s h o w n i n . t a b l e 6 rev. 0 | page 10 of 24
ADT7461 table 6. temp erature data format (local and remote temp erature high by te) 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. 2 binary s c ale temperature meas urement re turns 0 f o r al l t e mpe r ature s < 0 c . 3 binary scale temperature measur ement re turns 127 for a l l temperature > 127c. the us er ma y s w i t ch b e tw e e n m e as ur e m en t ra n g es a t an y t i me. s w i t c h i n g th e r a n g e w i ll a l s o s w i t c h th e d a ta f o rm a t . t h e n e x t t e m p era t ur e r e su l t fol l o w in g t h e sw i t chin g wi l l b e r e p o r t e d b a ck t o th e r e gi st e r in th e n e w f o rm a t . h o w e v e r , t h e co n t en t s o f th e limi t r e g i s t ers wil l n o t c h a n g e . i t is u p t o th e us er t o en s u r e tha t w h en t h e da t a fo r m a t cha n g e s, t h e li mi t r e g i s t e r s a r e r e p r o- g r a m m e d as ne cess a r y . m o r e info r m a t io n o n t h is ca n b e fo u n d in t h e s e c t io n . l i m i t re g i st e r s ADT7461 registers the ad t7461 c o n t a i n s 22 8-b i t r e g i s t ers in t o ta l . th es e r e g i s - t e rs a r e us e d t o s t o r e t h e r e s u l t s o f r e m o t e and lo cal t e m p er a t ure me a s ure m e n t s and h i g h and low t e m p er a t ure l i m i t s and t o c o n - f i gure and c o n t rol t h e de vi c e . a des c r i p t ion o f t h es e reg i s t ers fol l o w s, and f u r t her de t a i l s a r e g i ve n i n t a b l e 7 t h r o ug h t a b l e 11 . ad dress pointer r e gister the addr es s p o i n t e r r e g i s t er i t s e lf do es n o t ha v e , o r r e q u ir e , a n addr es s, as t h e f i rs t b y t e o f e v er y wr i t e o p era t ion is a u t o ma t i - ca l l y wr i t t e n t o t h is r e g i st er . t h e d a t a in t h is f i rst b y t e a l w a y s co n t a i n s t h e addr es s o f a n o t h e r r e g i s t er o n t h e ADT7461, which is st o r e d i n t h e addr ess p o in ter r e g i st er . i t is t o t h is r e g i st er addr ess t h a t t h e s e co nd b y te o f a wr i t e o p er a t ion is wr i t ten to or t o w h ich a subs e q uen t r e a d o p e r a t io n is p e r f o r m e d . the p o w e r - on defa u l t val u e o f t h e addr es s p o in t e r r e g i s t er is 000, s o if a r e ad o p era t io n is p e r f o r m e d im m e di a t e l y a f t e r p o w e r - o n , wi t h o u t f i rs t wr i t in g t o t h e addr es s p o in t e r , t h e val u e o f t h e lo cal tem p era t ur e w i l l b e r e t u r n e d , sin c e i t s r e g i s t er addr es s is 000. tem p er at ur e valu e r e giste r s the ad t7461 has thr e e r e g i s t ers t o s t o r e th e r e s u l t s o f lo cal and r e m o t e t e m p era t ur e m e as ur e m e n ts. th es e r e g i s t ers ca n o n l y b e wr i t t e n t o b y t h e ad c an d can b e r e ad b y t h e u s er o v er t h e s m bus. th e lo c a l t e m p era t ur e val u e r e g i s t er is a t a ddr es s 000 . the ext e r n al t e m p er a t ur e va l u e hig h b y te r e g i s t er is a t a d dr ess 001, wi t h t h e l o w b y t e r e g i s t er a t a ddr es s 01 0 . th e p o w e r - on d e f a u l t f o r a l l t h re e re g i ste r s i s 0 0 0 . c o nfigur ation r e gis t er the co nf igur a t i o n r e g i ster is a ddr ess 003 a t re ad and a d dr ess 009 a t wr i t e . i t s p o w e r - o n defa u l t is 000. onl y f o ur b i ts o f the co nf igura t io n r e g i s t er a r e us ed . b i ts 0, 1, 3, a n d 4 a r e r e s e r v ed a nd sh o u ld n o t b e wr i t te n to b y t h e us er . bi t 7 o f t h e conf igura t io n r e g i ster is us e d t o ma sk t h e aler t ou t p ut. i f bi t 7 i s 0 , t h e aler t o u t p u t is e n a b led . t h i s is th e p o w e r - o n def a u l t. i f bi t 7 is s e t to 1, t h e aler t output i s d i s - a b le d . t h is o n ly a p plies if pi n 6 is co nf igur e d as aler t . i f p i n 6 is co nf igur e d as therm2 , t h en t h e va l u e o f bi t 7 has n o ef fe c t . i f bi t 6 is 0, p o w e r - o n d e fa u l t, t h e de vic e is in op era t in g m o de w i t h t h e a d c co n v e r ti n g . i f b i t 6 i s se t t o 1, th e d e v i ce i s in st and b y m o de and t h e a d c do es n o t con v er t. the s m bus do e s , h o w e v e r , r e ma in ac ti v e in stand b y mo de , s o va l u es ca n be r e ad f r o m o r wr i t ten t o th e ADT7461 via t h e s m b u s in this m o de . the aler t and therm o u t p uts a r e a l s o ac t i ve in st an d b y m o de . c h a n g e s made t o t h e r e g i s t ers in s t and b y m o de t h a t af fe c t t h e therm or aler t o u t p uts wi l l c a us e t h es e sig n als to be u p d a t e d . b i t 5 det e r m in es th e conf igura t io n o f p i n 6 on th e ADT7461. i f b i t 5 is 0, (defa u l t ) th en p i n 6 is co nf igur ed as an aler t output . i f b i t 5 is 1, th en p i n 6 is conf ig ur ed as a therm2 ou t p ut. bi t 7 , th e aler t mask b i t, is o n ly ac t i v e w h e n pin 6 is conf ig ur e d as an aler t output . if p i n 6 i s s e tup a s a therm2 output , t h e n bi t 7 has no ef fe c t . bi t 2 s e ts t h e t e m p er a t ur e m e asur em en t ra n g e . i f bi t 2 is 0 (defa u l t va l u e), t h e tem p era t ur e m e as ur emen t r a n g e is s e t betw een 0c t o +127c. s e t t in g b i t 2 t o 1 m e a n s tha t t h e m e as - ur em en t ra n g e i s s e t t o t h e ext e n d e d t e m p era t u r e ra n g e . rev. 0 | page 11 of 24
ADT7461 tab l e 7. con f iguration register bit assign men t s bit name function power-on defau l t 7 mask1 0 = alert enabled 1 = alert mas k ed 0 6 run/stop 0 = run 1 = standby 0 5 alert / ther m2 0 = alert 1 = ther m2 0 4C 3 reserved 0 2 temperature range select 0 = 0c to 127c 1 = extended range 0 1C 0 reserved 0 conv ersion r a te register the con v ersio n ra t e r e g i st er is a ddr es s 004 a t re ad and a ddr es s 00a a t wr i t e . th e lo w e s t f o ur b i ts o f t h is r e g i s t er a r e us ed t o p r og ra m the con v ersio n ra te b y dividin g th e in t e r n al os cil l a t o r c l o c k b y 1, 2, 4, 8 , 16, 32, 64, 128, 256, 512, o r 1024 t o g i v e con v ersio n tim e s f r o m 15.5 m s (c o d e 00a) t o 16 s e con d s (c o d e 000). f o r exa m p l e , a con v ersio n r a t e o f 8 co n v er- sio n s/s e cond mea n s tha t b e g i nnin g a t 125 m s in t e r v als th e de vice p e r f o r m s a co n v ersio n on t h e in t e r n al and t h e ext e r n al t e m p era t ur e cha nne ls. this r e g i ster can b e wr i t ten to a nd r e ad b a ck o v er t h e s m bus. the hig h er fo ur b i t s o f t h is r e g i s t er a r e un us e d a nd m u st b e s e t t o 0. th e defa u l t val u e o f this r e g i s t er is 008, g i vin g a ra t e o f 16 co n v ersio n s p e r s e co nd . u s e o f s l o w er co n v ersio n t i m e s g r e a t l y r e d u ces t h e de vi ce p o w e r co n s u m p t ion, as sh o w n in . t a b l e 8 table 8. co nv e r sion rate regi ster codes code conversion/second average suppl y current a typ at v dd = 5.5 v 0 0 0 0 . 0 6 2 5 1 2 1 . 3 3 0 0 1 0 . 1 2 5 1 2 8 . 5 4 0 0 2 0 . 2 5 1 3 1 . 5 9 0 0 3 0 . 5 1 4 6 . 1 5 0 0 4 1 1 6 9 . 1 4 0 0 5 2 2 3 3 . 1 2 0 0 6 4 3 4 7 . 4 2 0 0 7 8 6 3 8 . 0 7 0 0 8 1 6 2 5 2 . 4 4 0 0 9 3 2 4 1 7 . 5 8 0 0 a 6 4 8 1 6 . 8 7 00b to 0ff reserved limit registers the ad t7461 has eig h t limi t reg i s t ers: hig h , lo w , an d therm t e m p era t ur e limi ts fo r b o t h lo ca l a nd r e m o t e te m p er a t ur e m e as ur e m en ts. the r e m o t e tem p era t ur e hig h and lo w limi ts sp a n t w o r e g i st e r s e a ch, t o co n t ain an u p p e r and lo w e r b y t e fo r e a ch limi t. th ere is als o a therm h y ste r e s is re g i ste r . a l l l i mi t r e g i s t ers can b e wr i t t e n t o an d re ad b a ck o v er t h e smbus. s e e f o r det a ils o f t h e limi t r e g i s t ers addr es s e s a nd t h eir po w e r - o n d e fa u l t v a l u e s . t a b l e 1 2 w h en pi n 6 is c o nf igur e d as an aler t output , t h e h i g h l i m i t r e g i s t ers p e r f o r m a > co m p a r is o n w h i l e t h e lo w limi t r e g i s t ers p e r f or m a c o m p ar i s on . f o r e x am pl e, i f t h e h i g h l i m i t re g i st e r is p r og ra mm e d wi t h 80c, t h en m e as ur in g 81c wil l r e s u l t in an o u t-o f -li m i t condi t i on, s e t t in g a f l a g in t h e s t a t u s r e g i s t er . i f t h e lo w limi t r e g i s t e r is p r og ra mm e d wi th 0 c, m e as ur in g 0c o r l o we r w i l l re su lt i n a n out - of - l i m it c o n d i t i o n . ex ceed i n g ei th er th e l o cal o r r e m o t e therm limi t ass e r t s therm lo w . w h en pin 6 is co nf igur ed as therm2 , e x ceed i n g ei t h er t h e lo cal o r r e m o t e hig h l i mi t as s e r t s therm2 lo w . a defa u l t h y ster esis va l u e o f 10c is p r o v ide d t h a t a p plies t o b o t h therm cha n n e ls. this h y s t er esis val u e ma y b e r e p r og ra mm e d to an y v a lu e af te r p o we r up ( r e g i s te r a d dre s s 0 2 1 ) . i t is im p o r t an t to r e m e m b er t h a t t h e t e m p era t u r e limi ts da t a fo r m a t is t h e s a m e as t h e t e m p era t ur e m e as ur e m e n t da t a fo r m a t . s o if t h e t e m p era t ur e me as ur emen t us e s defa u l t b i na r y , t h e n t h e t e m p er a t ur e li mi ts als o us e t h e b i na r y s c ale . i f t h e t e m p era t ur e m e as ur emen t s c ale is sw i t ch e d , h o w e v e r , t h e t e m p era t ur e limi ts do n o t s w i t ch a u t o ma t i cal l y . the us er m u s t r e p r og ra m t h e l i mi t reg i s t ers t o t h e desir e d val u e in t h e co r r e c t da ta f o rm a t . f o r e x a m p l e , i f th e r e m o t e lo w li mi t i s se t a t 10 c a nd t h e def a u l t b i na r y s c ale is b e in g us e d , t h e li mi t r e g i st er val u e sh o u ld be 0000 1010b . i f th e s c ale is s w i t ch e d t o o f fs et b i na r y , t h e v a l u e in t h e lo w t e m p era t ur e limi t r e g i s t er sh o u ld b e r e p r og ra mm ed t o be 0100 1010 b . status r e gis t e r the s t a t us r e g i s t er is a r e ad-only r e g i s t er , a t a d dr es s 002. i t co n t a i n s s t a t us inf o r m a t io n f o r th e ADT7461. bi t 7 o f t h e st a t us r e g i s t er indic a t e s t h a t t h e ad c is b u sy co n - v e r t in g w h en i t is hig h . t h e o t her b i ts in t h is r e g i st er f l a g t h e o u t-o f -li m i t t e m p er a t ur e m e asur em en ts (bi t s 6C3 a nd bi ts 1C 0) an d t h e re mote s e ns or op e n c i r c u i t ( b it 2 ) . i f p i n 6 is co n f igur e d a s a n aler t outp ut , t h e fo l l ow i n g a p pl i e s. i f t h e lo cal t e m p era t ur e m e as ur em en t e x ce e d s i t s li mi ts, bi t 6 (hi g h limi t) o r b i t 5 (l o w limi t) o f th e s t a t us r e g i s t e r as se r t s t o f l a g th is co n d i t io n. i f t h e r e m o t e t e m p e r a t ur e m e as ur em en t e x ce e d s i t s lim- i t s, t h en bi t 4 (hi g h limi t) o r bi t 3 (lo w limi t ) ass e r t s. bi t 2 ass e r t s t o f l a g a n o p en-ci r cui t co n d i t io n o n t h e r e m o t e sen s o r . th es e f i v e f l a g s a r e n o r d t o g e th er , so if a n y o f th em is hig h , t h e aler t i n te r r upt la t c h wil l be s e t a n d th e aler t o u t p u t wil l g o l o w . rev. 0 | page 12 of 24
ADT7461 readin g t h e s t a t us r e g i s t er wil l clea r th e f i v e f l a g s, b i ts 6C2, p r o v ided t h e er r o r co n d i t io n s tha t c a us e d the f l ags t o be s e t h a v e g o n e aw ay . a f l a g b i t c a n o n l y b e r e s e t i f t h e c o r r e s p o n d i n g va l u e r e g i st er con t a i n s an in -lim i t m e a s ur em e n t o r if t h e s e n s o r i s g ood . the aler t in t e r r u p t l a t c h is n o t r e s e t b y r e adin g t h e st a t us re g i ste r . i t w i l l b e re s e t w h e n t h e aler t o u t p u t ha s been s e r v ice d b y t h e mas t er r e adin g t h e de vice addres s, p r o v ide d t h e er r o r co n d i t ion has go ne a w a y and t h e st a t us r e g i ster f l a g b i ts h a v e been r e se t . w h e n f l ag 1 a n d / or f l ag 0 are s e t , t h e therm output g o e s l o w t o indic a te t h a t t h e tem p era t ur e m e as ur emen t s a r e o u tside t h e p r o g ra mm e d li mi ts. t h e therm output d o e s not ne e d to b e re s e t , u n l i ke t h e aler t o u t p ut. on c e t h e m e as ur e m en ts a r e wi t h in t h e limi t s , t h e co r r es p o ndin g st a t us r e g i st er b i ts a r e r e s e t a u t o ma ticall y , a n d th e therm o u t p u t go es hig h . the us er ma y add h y s t er esis b y p r og ra mmin g reg i st er 021. the therm o u t p ut w i l l b e r e s e t o n ly w h e n t h e tem p era t ur e fa l l s t o limi t val u eC h y s t er esis val u e . w h en pi n 6 is c o nf igur e d as therm2 , o n l y t h e hig h te m p er a - t u re l i m i t s are rel e v a n t . i f f l ag 6 an d / or f l ag 4 are s e t , t h e therm2 o u t p u t go es lo w t o in dica t e tha t t h e t e m p era t ur e m e as ur e m en ts ar e o u tside t h e pr og ra mm e d li mi ts. fla g 5 and fla g 3 ha ve n o ef f e c t o n therm2 . t h e b e h a v i or of therm2 is o t h e r w is e t h e s a m e as therm . tab l e 9. status register bit as sign men t s bit name function 7 busy 1 when adc converting 6 lhigh* 1 when local hi gh temperature limit tripped 5 llow* 1 when local low temperature limit tripped 4 r h i g h * 1 wh en remo te high tempe r atur e li mi t tr ipped 3 r l o w * 1 wh en remo te low tempe r atur e li mi t tr ipped 2 open* 1 when remote sensor open circuit 1 rthrm 1 when remote ther m limit tripped 0 lthr m 1 when local ther m limit tripped *th e se fla g s st a y h i gh un t i l t h e st a t us r e gi st er i s r e a d , or t h e y a r e re set by por . offset r e gister of fs et er r o rs ma e in t r o d uce d in t o t h e r e m o t e t e m p er a t ur e m e as ur e m en t clo c n o is e o r t h e t h er mal dio d e e i n g lo ca te d a a f r o m t h e h o t sp o t t o achi e v e t h e s p e c if ie d acc u - rac o n this c h a nne l th es e o f fs ets m u s t e r e m o v e d the o f fs et val u e is s t o r e d as a - i t t os com p l e m e n t va l u e in reg i st ers hig h te a nd lo t e lef t u s t if ie d onl t h e up p e r i t s o f r e g i s t er a r e us e d the s o f reg i st er is t h e sig n i t the mini m u m o f fs et t h a t can e p r og ra mm e d is c a nd t h e maim u m is c th e val u e in t h e o f fs et r e g i s t er is adde d o r s u t rac t e d t o t h e m e as - ur e d val u e o f t h e r e m o te t e m p e r a t ur e the o f fs et r e g i s t er p o e rs u p i t h a def a u l t va l u e o f c an d il l ha v e n o ef fe c t unles s t h e us er r i t es a dif f er en t val u e t o i t tale sam p le offset register codes offset val u e 011 012 ?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 reg i ster the on e- sh o t r e g i s t er is us e d t o ini t i a t e a con v ersio n an d com - p a r i s o n c cle h e n t h e a d t is in s t a n d m o de a f t e r h ich t h e de vic e r e t u r n s t o st and r i t in g t o t h e on e - sh o t r e g i s t er addr es s f ca us es th e adt t o p e r f o r m a co n - versio n a nd com p a r is o n o n o t h t h e in ter n a l and t h e e ter n a l tem p er a t ur e ch a nnels this is no t a da t a r e g i ste r as such an d i t is t h e r i t e o p er a t io n t o a d dr ess f t h a t c a us es t h e on e - sh o t co n v ersio n the d a t a r i t te n to t h is addr ess is ir r e le van t and is not store d consecu t i v e alert register th e v a lu e r it te n to t h i s re g i ste r de te r m i n e s ho ma n out - of - limi t m e asur e m en ts m u st o c c u r e fo r e a n aler t i s ge ne r a te d the def a u l t val u e is t h a t on e o u t - o f -limi t m e as u r em e n t g e n e r- at e s a n aler t th e ma i m u m va l u e t h a t c a n e ch o s e n is the p u r p os e o f t h is r e g i s t er is to al lo t h e us er t o p e r f o r m s o me f i l t er in g of t h e o u t p u t th is is p a r t ic u l a r l us ef u l a t t h e fas t est t h r e e con v ersio n ra t e s h er e n o a v er a g i n g t a e s plac e this r e g i st er is a t a ddr ess tale co ns ecutive alert register it register val u e n u mber of ou t-of-limit measurements require d y 000 1 y 001 2 y 011 3 y 111 4 = do nt care bit. y = sm bus time o u t bit. de f a ul t = 0. s ee s m b u s se ctio n f o r more inf o rmation. rev. 0 | page 13 of 24
ADT7461 table 12. list o f ADT7461 reg i sters read a ddres s ( h ex) write a ddress ( h ex) name power-on defa ult not applicab le not applicab le ad d r ess pointer und e fined 00 not applicable local temperat ure value 0000 0000 (00 0) 01 not applicable external tempe r a ture value hig h byte 0000 0000 (00 0) 02 not applicable status undefined 03 09 configuration 0000 0000 (00 0) 04 0a conversi on rate 0000 1000 (00 8) 05 0b local temperat ure high limit 0101 0101 (05 5) (85c ) 06 0c local temperat ure low limit 0000 0000 (00 0) (0c ) 07 0d external tempe r ature high l imi t high byte 0101 0101 (05 5) (85c ) 08 0e external tempe r ature low l imit high byte 0000 0000 (00 0) (0c ) not applicab le 0f one-shot 10 not applicable external te mpe r ature value low byte 0000 0000 11 11 external tempe r ature offset hi gh byte 0000 0000 12 12 external tempe r atur e offset low byte 0000 0000 13 13 external tempe r ature high limi t low byte 0000 0000 14 14 external tempe r ature low limit low byte 0000 0000 19 19 external ther m limit 0110 1100 (05 5) (85c ) 20 20 local ther m limit 0101 0101 (05 5) (85c ) 21 21 ther m hysteresis 0000 1010 (00 a) (10 c) 22 22 consecutive alert 0000 0001 (00 1) fe not applicable manufacturer id 0100 0001 (04 1) ff not applicable die revision code 0101 0001 (05 1) *writing to addr ess 0f causes the adt 7461 to perform a single measu r ement. it is not a data regi ster as such and it does not ma tte r what d a ta is writte n to i t . serial bus interface c o n t r o l o f th e ADT7461 is ca r r i ed o u t via the s e r i al b u s. th e ADT7461 is conn ec t e d t o this b u s as a sla v e de vice , u n der t h e co n t r o l o f a mast er de vice. the ad t7461 has a n s m b u s tim e o u t f e a t ur e . w h en this is en- a b led , t h e s m bus wil l tim e o u t a f t e r typ i cal l y 25 m s o f n o ac tiv- i t y . h o w e v e r , t h i s fe a t ur e is n o t e n a b le d b y def a u l t. bi t 7 o f t h e co n s ec u t i ve aler t r e g i s t er (a ddres s = 022) s h ou ld be s e t t o ena b le i t . the ad t7461 su p p o r ts p a c k et er r o r c h ec kin g ( p ec) a nd i t s us e i s o p ti o n al . i t i s tri g g e r e d b y s u p p l yi n g t h e e x tra c l oc k f o r th e p e c b y t e . th e pec b y t e is calc u l a t e d usin g c r c-8. th e f r am e ch e c k s e q u e n c e (fcs) co nfo r m s t o cr c-8 b y t h e p o l y n o mial () 1 1 2 8 + + + = x x x x c c o n s u l t t h e s m bus 1.1 sp e c if ic a t io n fo r m o r e i n fo r m a t io n (w w w .s m b us.o rg). addressi n g the de vi ce i n g e n e ral , e ver y s m b u s de vice has a 7-b i t de v i ce addr es s, excep t fo r s o m e de vices t h a t h a ve ex tende d , 10-b i t ad dr ess e s. w h en t h e mas t er de vice s e n d s a de vic e addr es s o v er t h e b u s, t h e s l a v e device wi t h tha t addr es s wil l r e s p ond . th e ADT7461 is a v a i la b l e wi th on e de vice addr es s, 04c (1001 100b). the s e r i al b u s pr o t o c ol o p era t es as fol l o w s: 1. the mas t er ini t i a t e s da t a t r an sfer b y es t a b l is hing a st a r t co ndi t i on, def i ne d as a hig h -to - lo w t r a n si t i o n on t h e s e r i a l da t a line s d a t a, w h i l e t h e s e r i al clo c k li n e sc lk r e ma in s hig h . thi s i n di c a t e s t h a t an ad d r ess/d a t a st r e am wi l l fol l o w . a l l sla v e p e r i pher a l s co nn e c te d to t h e s e r i a l b u s r e sp o nd to t h e st ar t condi t i on and shif t in t h e n e x t eig h t b i ts, co n - sis t in g o f a 7-b i t addr es s (ms b f i rs t) p l us a n r / w bi t , w h ich deter m i n es t h e dir e c t io n o f t h e da t a t r a n sfer , i . e., whether da t a wi l l be wr i t t e n t o o r r e ad f r o m the s l a v e de vice . the p e r i ph eral w h os e addr es s co r r es p o n d s t o t h e tra n sm i t t e d a ddr es s r e s p o n ds b y p u lli n g th e da ta lin e lo w d u ri n g th e l o w pe ri od be f o r e th e n i n t h c l oc k p u l s e , kn o w n a s t h e a c k n ow l e d g e bit . a l l ot h e r d e v i c e s on t h e bu s now r e ma in idle whi l e th e s e lec t e d device wai t s f o r da ta t o b e re a d f r om or w r i tte n to i t . i f t h e r / w bit i s a 0 , t h e m a s t e r wil l wr i t e t o t h e s l a v e de vi ce . i f t h e r / w bit i s a 1 , t h e m a s - t e r wi l l r e ad f r o m t h e s l a v e de vi ce . 2. da ta i s sen t o v e r th e s e rial b u s in a seq u en ce o f n i n e c l oc k p u ls e s , ei g h t b i ts o f da t a fol l o w e d b y a n a c k n ow l e dge bi t f r o m t h e s l a v e de vi ce . t r a n si tio n s o n t h e da t a l i ne m u s t oc cur d u rin g th e l o w pe riod o f th e c l oc k s i gn al a n d r e m a in st ab l e du r i ng t h e h i g h p e r i o d , s i n c e a l o w - to - h i g h t r a n s i t i o n w h en t h e c l ock is hi g h ma y b e in t e r p r e t e d a s a s t o p signal . the n u m b er o f da t a b y t e s t h a t c a n b e t r an smi t te d o ver t h e rev. 0 | page 14 of 24
ADT7461 se r i al b u s in a s i n g le r e ad o r w r i t e o p e r a t io n is limi t e d o n l y b y w h a t t h e mast er and sl a ve de v i ce s can hand le. 3. w h en al l da ta b y t e s ha v e been read o r wr i t t e n, st o p co ndi - t i o n s a r e es t a b l i s h e d . i n wr i t e mo de , t h e mast er wi l l p u l l t h e da ta line hig h d u r i n g th e t e n t h c l o c k p u ls e t o as s e r t a s t o p co ndi t i on. i n r e ad m o de , t h e mas t er de vice wi l l o v err i de th e a c k n o w le d g e b i t b y p u lli n g th e da ta lin e h i g h d u ri n g th e lo w pe ri od be f o r e th e n i n t h c l oc k p u lse . t h is i s kn o w n as n o a c kn o w le dg e . th e mas t er wi l l t h en t a k e t h e da t a l i n e lo w d u r i n g t h e l o w p e r i o d b e fo re t h e t e n t h clo c k p u ls e , t h e n hig h d u r i ng t h e ten t h clo c k p u ls e t o ass e r t a s t op co ndi t i on. an y n u m b er o f b y t e s o f da t a ma y b e t r an sfer r e d o v er t h e s e r i al b u s in on e op er a t io n, b u t i t is no t p o ssi b le t o m i x r e ad an d wr i t e in on e o p era t ion b e c a us e t h e ty p e o f o p era t ion is det e r m i n e d a t t h e b e g i nni n g and ca n n ot subs e q uen t ly b e chan ge d w i t h ou t s t a r tin g a new op era t ion. i n t h e cas e o f t h e ADT7461, wr i t e o p era t io ns co n t a i n e i t h er o n e or tw o b y t e s, w h i l e r e ad o p era - ti o n s co n t a i n o n e b y t e . t o wr i t e da t a t o o n e o f t h e de vice da t a r e g i s t ers o r t o r e ad da ta f r o m i t , t h e a d d r e s s po i n t e r r e gi s t e r m u s t b e se t so th a t th e co r r e c t da t a r e g i s t er is addr es s e d . th e f i rs t b y te o f a wr i t e op era - ti o n al wa ys co n t a i n s a vali d ad dr es s tha t is st o r e d in t h e addr es s p o i n te r re g i ste r . i f da t a i s to b e w r it te n to t h e d e v i c e , t h e w r i t e op e r a t i o n c o n t a i ns a s e c o nd d a t a b y te t h a t i s w r i tte n to t h e r e g i s t er s e le c t e d b y t h e addr es s p o in t e r r e g i s t er . this is i l l u st ra t e d i n . the d e v i ce ad dr ess is s e n t o v er t h e b u s fol l o w ed b y r/ w s e t t o 0. this is fol l o w e d b y tw o d a t a b y t e s. the f i rs t da t a b y te is t h e addr es s o f t h e in t e r n al da t a re g i ste r to b e w r i t te n to , w h i c h i s store d i n t h e a ddre s s p o i n t e r re g i ste r . th e s e c o nd d a t a b y te i s t h e d a t a to b e w r it te n to t h e in t e r n a l d a t a r e g i st er . f i gur e 1 5 f i gur e 1 5 . 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 04110-0-003 a6 19 1 a5 a4 a3 a2 a1 a0 rw d7 d6 d5 d4 d3 d2 d1 d0 scl sdat 9 a start b master ac. b ADT7461 frame 1 serial bus address bte frame 2 address pointer reister bte frame 3 data bte scl (continued) sdata (continued) ac. b ADT7461 ac. b ADT7461 stop b master 9 1 d7 d6 d5 d4 d3 d2 d1 d0 04110-0-004 scl s dat a start b master ac. b ADT7461 ac. b ADT7461 stop b master frame 1 serial bus address bte frame 2 address pointer reister bte 19 1 a6 a5 a4 a3 a2 a1 a0 rw d7 d6 d5 d4 d3 d2 d1 d0 9 f i g u re 16. 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 scl sdata start b master ac. b ADT7461 frame 1 serial bus address bte frame 2 data bte from ADT7461 ac. b ADT7461 stop b master 19 1 9 a6 a5 a4 a3 a2 a1 a0 rw d7 d6 d5 d4 d3 d2 d1 d0 f i g u re 17. 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 rev. 0 page 15 of 24
ADT7461 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 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: ? 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 f i rst n e cess a r y t o s e t i t t o t h e c o r r e c t v a lu e b e f o re d a t a c a n b e re a d f r om t h e d e s i re d d a t a r e g i s t er . this is do ne b y p e r f o r min g a wr i t e t o t h e ADT7461 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 nin g t h e re g i ste r re a d a d dre s s i s s e n t , a s d a t a i s not to b e w r i tte n to t h e r e g i st er . thi s is s h own i n f . 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 gi s t e r . t h i s i s sh o w n in . i gur e 1 6 i gur e 1 6 f i gur e 1 7 ? 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 al r e ad y a t t h e desir e d ad dr ess, d a t a ca n b e r e ad f r o m t h e co r r esp o n d i n g da t a r e g i s t er wi t h o u t f i rs t wr i t ing t o t h e addr es s p o in t e r r e g i ster an d t h e b u s t r a n s a c t ion sh own i n f c a n b e om itte d. no t e s 1. al th o u g h i t is p o s s i b le t o r e ad a da ta b y te 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 ad dr ess p o in t e r r e g i st er is a l r e ad y a t t h e c o r r e c t va l u e , i t is n o t p o ss i b le t o wr i t e d a t a t o a r e g i st er wi t h ou t wr i t in g t o t h e addr es s p o in t e r r e g i st er b e ca us e t h e f i rst da t a b y te o f a wr i t e is al w a ys wr i t t e n t o t h e addr es s p o i n t e r reg i s t er . 2. do n o t f o rg et tha t s o m e o f t h e ADT7461 r e g i s t ers ha v e dif f er en t addr ess e s fo r r e ad a n d wr i t e op era t ions. th e wr i t e addr ess o f a r e g i ster m u st b e wr i t te n to t h e addr ess p o in t e r if d a t a is t o b e wr i t t e n to t h a t r e g i st er , b u t i t m a y n o t be p o s s i b le t o r e ad da t a f r o m tha t addr es s. the r e ad addr ess o f a r e g i ster m u st b e wr i tten to t h e address p o i n ter bef o r e da t a can be r e ad f r o m tha t r e g i st er . alert output this is a p plicab le w h en pin 6 is co nf igur e d as an aler t output . t h e aler t o u t p u t g o es lo w w h ene v er a n ou t-of-limi t m e as ur e m en t is det e c t e d , o r if t h e r e m o te t e m p era t ur e s e n s o r i s o p en cir c ui t. i t is a n o p en-dra in o u t p u t an d r e q u ir es a p u l l -u p to v dd . s e v e r a l aler t o u t p u t s can b e wire-or e d to get h e r , s o t h a t t h e c o m m on l i n e w i l l go l o w i f one or more of t h e aler t output s go e s 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 c es s o r , o r i t ma y b e us ed as a n sm b a l e r t . s l a v e devi ces o n th 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 mas t er tha t t h e y w a n 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 co mm o n sm b a l e r t lin e c o nn e c te d to t h e master . w h e n th e sm b a l e r t lin e is p u l l ed lo w b y o n e o f th 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 a s ill u s t r a t e d i n f . i gu r e 1 8 f i g u re 18. 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 u t is lo w , th 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 e r 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 output s we re l o w h a ve re s p o n d e d. low power standb 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 conf igura t ion 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 00f), a f t e r w h ich t h e de vice wi l 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 the ad t7461 has s e n s o r f a u l t det e c t ion cir c ui tr y in t e r n al l y a t i t s d+ i n p u t. this cir c ui t can de t e c t si t u a t io n s w h er e an ext e r n al r e m o t e dio d e is n o t con n e c t e d , o r is in co r r e c t l y co nne c t e d , t o rev. 0 page 16 of 24
ADT7461 th e ADT7461. a sim p le v o l t a g e co m p a r a t o r tr i p s if th e v o l t a g e a t d + e x ceed s v dd ?1 v (typ ical), signif yin g a n o p en cir c ui t b e t w e e n d + a n d d ? . t h e output of t h i s c o m p ar a t or i s c h e c ke d w h en a con v ersio n is ini t i a te d . bi t 2 o f t h e s t a t us r e g i s t 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 i s e n a b l e d, se t t in g th i s f l a g w i ll ca u s e aler t to a s s e r t l o w . i f th 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 the ADT7461, th en in o r der t o p r even t t h e o p e n f l a g b e in g s e t co n t i n uo us l y , t h e us er s h o u ld t i e t h e d+ an d d ? in p u ts o f t h e ADT7461 t o g e th er . m o s t te m p er a t u r e s e n s i n g dio d e s ha ve an op er a t ing t e m p er a t ur e ra n g e o f ?5 5 c t o + 1 5 0 c . a b o v e 15 0 c , th ey l o s e th e i r s e mi co 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, s e t t i n g t h e op e n f l ag. the ex ter n a l di o d e i n t h is c a s e wi l l n o lon g e r g i ve an acc u r a te t e m p er a t ur e m e as - ur e m en t. a r e ad o f t h e t e m p er a t ur e r e s u l t r e g i s t e r wi l l g i ve t h e last go o d te m p e r a t ure me asur e m e n t. the us er sho u l d b e a w a r e t h a t , w h i l e t h e di o d e f a u l t i s t r ig ger e d , t h e te m p er a t ure me asur e - me n t on t h e ex ter n a l chan nel m a y not b e a c c u r a te. 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 ha 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 - t u r e limi ts o r a n o p en-c ir c u i t f a u l t o n t h e ext e r n al dio 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 o u t p u t is as s e r t e d lo w . an o p en-cir c u i t 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 ha s go n e a w a y , and t h e st a t us re g i ste r h a s b e e n re s e t . 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 era - t u r e e x ceed s th e p r ogra m m ed therm limi ts. the therm t e m p era t ur e limi ts sh o u ld n o r m al l y be e q ual t o o r g r e a t e r tha n t h e hig h tem p era t ur e li mi ts. therm is r e s e t a u t o m a t i ca l l y w h en t h e t e m p e r a t ur e fal l s b a ck wi t h in t h e therm limi t. th e ext e r n al therm limi t is s e t b y defa u l t to 85c, as is t h e lo ca l therm limi t. a h y st er e s is va l u e ca n b e p r og ra mm e d , in w h ich cas e , therm wi l l r e s e t w h en t h e t e m p e r a t ur e fal l s t o t h e limi t val u e mi n u s t h e h y s t er esis val u e. this a p plies t o b o t h lo cal and r e m o t e me as ur 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 va l u e is 10c, b u t t h is ma y b e rep r og ra mm e d to a n y va l u e a f te 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 i 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 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 t o sig n al t o t h e h o s t v i a t h e s m bus t h a t t h e t e m p er a t ur e has r i s e n. the us er co u l d us e t h e therm outpu t t o tu r n o n a f a n t o co ol t h e syst em, if t h e t e m p er a t ur e co n t in ues t o in 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 . f i gur e 1 9 f i g u re 19. o p er at i o n of t h e aler t and therm i n t e rrupts f i gur e 1 9 04110- 0- 007 1 3 2 4 therm limit hih temp limit therm limit-hsteresis reset b master alert therm 100 1. i f t h e m e as ur e d t e m p era t ur e ece 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 ece 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 used t o th r o t t le th e c p u c l oc k o r sw i t c h o n a fa 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 , 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 ece e d s t h e p r og ra mme d lo cal a ndo 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 . rev. 0 | page 17 of 24
ADT7461 f i ur e f i g u re 20. o p er at i o n of t h e therm and therm2 i n t e rrupts f i gur e 2 0 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 a m p l e , th e therm2 limi ts a r e s e t lo w e r t h a n t h e therm limi ts. the therm2 o u t p u t co u l d be us ed t o t u r n o n a fan. i f t h e tem p er a t ur e con t in ues t o r i s e and ece 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 1. wh e n t h e therm2 l i m i t i s e 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 ece 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 , 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 . the t e m p er a t ure m e as ur e m en t co u l d b e e i t h er t h e lo c a l o r t h e et e r n al t e m p er a t ur e m e as ur e m en t. 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 en vir o nm en ts p r e v i- o u s p r ac t i ce a s t o pl ac e a c a p a c i t o r acr o ss t h e d and d pins t o hel p com a t t h e ef fe c t s o f no i s e o e v e r l a rge c a p a ci t a n c es a f fe c t t h e acc u r a c o f t h e t e m p er a t ure me asur e m en t le adi n g t o a r e commende d ma i m u m c a p a ci t o r va l u e o f pf h il e t h is ca paci t o r ill r e d u c e th e n o i s e i t ill n o t e l i m i n a t e i t m ai n g i t dif f ic u l t t o us e t h e s e n s o r i n a ve r no is e n v i ro nme n t the ad t has a ma o r adva n t a g e o v er o t her de vices 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 et 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 s a f i l t er t o e co n s t r uc t e d e t e e n t h e et 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 f i l t er r e s i s t a n ce s e en in s e r i e s i 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 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 s th e ad t 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 in n o is en vir o nm e n ts f s h o s a lo -p a ss r - c - r f i l t er i t h t h e fol l o ing val u es r a nd c nf this f i l t er in g r e d u ces o th co mm on-mo d e n o is e an d dif f er en t i al n o is e i gur e f i g u re 21. f i lte r b e t w een r e m o te s e ns or and a d t7 4 61 04110-0-009 d+ 1nf 100 ? ? factors affecting diode accur a cy remote sensi n g diode the ad t is desig n e d t o o r i th s u stra t e tra n sis t o r s u il t in t o p r o c es s o rs o r i t h dis c r e t e tra n sis t o r s s u s tra t e tra n sis t o r s il l g e n e ral l e pnp tp e s i t h t h e col l e c t o r co nne c t e d t o t h e s u s t r a t e dis c r e t e tp e s ca n e ei t h er pnp o r npn t r a n sisto r co nne c t e d as a dio d e as e sh or te d to col l e c to r f a n np n tra n s i s t o r i s used th e co ll ect o r a n d a se a r e co nne c t e d to d a nd t h e em i t ter to d f a pnp t r a n sisto r is us e d t h e col l e c to r a n d a s e a r e co nne c t e d to d a nd t h e e m it te r 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 o t h s u s t r a t e an d dis c r e t e tra n sisto r s a n u m er of fac t o r s s h o u ld e ta e n in t o co n s idera t ion ? n f f e n i i e e f e e vi i n f e e l i e f i el e vi t e ti ief n n f vl e f tef l l in e i n e e l l e ee in e e e etc e n in n i e n f en e l c n l e e eef e n f vl e ( ) ( ) t kelvin n t f + = ? ?
ADT7461 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 i n 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 (s a y 50 t o 150) tha t in dic a t e s tig 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 2 n 3904, 2n3906, o r eq ui valen t s in sot - 2 3 p a ck age s , are su i t abl 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 i n 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 i n g m e asur e d . a n u m b er o f fac t o r s ca n a f f e ct th i s . i d eall y , th e se n s o r sh o u ld be in g o o d th e r m a l co n t a c t wi t h t h e p a r t o f th e sys t em being m e as ur ed . i f i t is n o t, t h e t h er mal i n er t i a ca us e d b y t h e s e n s o r s mas s w i l l ca us e a l a g in t h e r e s p on s e o f t h e s e n s o r t o a tem p er a t ur e chan g e . i n t h e cas e of t h e re mo te s e ns or , t h i s shou l d not b e a pro b l e m , s i n c e it w i l l ei t h er b e a s u bs t r a t e t r a n sist o r i n t h e p r o c es s o r o r ca n b e a smal l p a ckage de vic e , su ch as s o t - 2 3 , pl ac e d in cl o s e p r o x imity to i t . t h e on - c h i p s e ns or , howe ve r , w i l l of te n b e re mot e f r om t h e p r o c ess o r an d wi l l o n ly b e m o ni to r i n g t h e ge ner a l a m b i e n t t e m p era t ur e a r o u n d t h e p a cka g e . the t h er mal t i me co n s t a n t o f th e so i c -8 p a cka g e in stil l a i r is a b o u t 140 s e c o n d s, and if the a m b i e n t air t e m p era t ur e q u ickly cha n g e d b y 10 0 deg r e e s, i t w o uld ta k e a b o u t 12 m i n u t e s (5 ti m e co n s ta n t s) f o r th e j u n c tio n t e m p era t ur e o f th e ADT7461 t o s e t t le wi thin 1 deg r ee o f this. i n p r ac tice , th e ADT7461 p a c k a g e wil l be in e l ec tr ical , an d h e n c e t h er ma l, co n t ac t w i t h a pcb and ma y a l s o b e i n a fo r c e d air f lo w . h o w acc u ra t e l y t h e tem 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 asur e d wi l l a l s o a f fe c t th e a c cura c y . s e lf- h e a ti n g d u e t o th e po w e r d i ssi pa t e d in th e ADT7461 o r the r e m o te s e ns o r ca us es t h e c h i p t e m p era t ur e o f t h e de vice 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 ver , t h e c u r r e n t f o rc e d t h rou g h t h e re m o te s e ns or i s s o s m a l l t h a t s e l f - h e a t i n g i s n e gligi b le . i n th e cas e o f th e a d t 7 461, th e w o r s t - case co ndi tion o c c u rs w h en t h e de vice is co n v er tin g a t 64 con v er- sio n s p e r s e cond while sinkin g th e maxim u m c u r r en t o f 1 ma at t h e aler t a nd therm o u t p u t . i n th i s ca s e , th e t o tal po w e r dissi p a t io n i n t h e de vic e is a b out 4.5 m w . t h e t h er ma l r e sis- ta n c e , ja , o f th e so i c -8 p a c k a g e is a b o u t 121c/w . laout 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 : ? 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 i d e d t h a t t h e w o rst n o is e s o ur ces, i . e . , clo c k gen e r a to rs, d a t a /addr ess b u s e s, a nd cr t s , a r e a v o i de d , t h is dis t an c e can be 4 in ch es t o 8 in ch es. ? ro u t e t h e d+ and dC t r acks clos e t o g e t h er , in p a ral l e l , wi t h g r o u nde d gua r d t r acks on e a ch side. t o mi nimi 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 22. t y pic a l a r r a ng e m ent of sig n al t r ack s ? 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 . ? 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. ? 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. rev. 0 page 19 of 24
ADT7461 ? 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 s h ie lde d twis t e d p a ir , s u ch as b e lden n o . 8451 micr o p h o n e ca b l e . c o nn e c t t h e t w i s te d p a ir to d+ a nd d? and t h e shield to gnd c l os e t o t h e ADT7461. l e a v e t h e r e m o te end o f th e sh i e l d u n c o n n e c te d to a v oi d g r ou nd l o op s . 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 tan c e can a f f e c t th 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. applic ati o n circuit f i gur e 2 3 f i gure 23. t y pic a l a p plic at ion cir c u i t 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 alr e ad y p r o v ide d e l s e w h er e i n t h e sys t em. 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 3.6 v tp 10k ? ? rev. 0 page 20 of 24
ADT7461 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) 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 ma 3.00 bsc coplanarit 0.10 0.23 0.08 compliant to jedec standards mo-187aa f i g u re 25. 8-l e ad m i cro s m al l o u t l in e p a ckag e msop (rm-8) di me nsio ns sho w n i n mi ll im e t e r s ordering guide model operating temperature r a nge package descri ption package option brand i ng information smbus addres s ADT7461ar ?40c to +125c 8-lead so ic package r-8 ADT7461ar 4c ADT7461ar- ree l ?40c to +125c 8-lead soic package r-8 ADT7461ar 4c ADT7461ar- ree l 7 ?40c to +125c 8-lead soic package r-8 ADT7461ar 4c ADT7461arm ?40c to +125c 8-lead msop pa ckage rm-8 t1b 4c ADT7461ar m -r eel ?40c to +125 c 8-lead msop pa ckage rm-8 t1b 4c ADT7461ar m -r eel7 ?40c to +125 c 8-lead msop pa ckage rm-8 t1b 4c eval-ad t7461e b ADT7461 evalua tion board rev. 0 page 21 of 24
ADT7461 notes rev. 0 | page 22 of 24
ADT7461 notes rev. 0 | page 23 of 24
ADT7461 rev. 0 | page 24 of 24 notes ? 2003 a n alo g devic e s, inc. all rig h ts res e rve d . t r ade m arks a n d re g i s - tered trade m arks are the property of their respective owners . c04110-0-10/03(0)

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