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128-position i 2 c compatible digital resistor ad5246 features 128-position end-to-end r e s istance 5 k?, 1 0 k?, 50 k?, 10 0 k? ultracompact sc70-6 (2 mm 2.1 mm) packa g e i 2 c? compatibl e interface full re ad/write of wiper register power-on preset to midscale single supply 2 . 7 v to 5. 5 v low temperature coefficient 4 5 ppm/c low power, i dd = 3 a typical wide operatin g temperature C40c to +125 c evaluation board available applic ati o ns mechanical pot e ntiometer replacement in ne w designs rev. 0 transducer adj u stment of pre ssure, tempera t ure, position, chemical, and optical sensors rf amplifier bi asing automotive e l ectronics adjustment gain control and offset a d just ment general overview the ad5246 p r o v ides a com p ac t 2 mm 2.1 mm p a c k a g e d s o l u tio n f o r 128-p o si tio n ad j u s t m e n t a p p l ic a t ion s . this de vice p e r f or ms t h e s a me el e c t r on i c a d j u st me n t f u nc t i on a s a v a r i a b l e r e sisto r . a v a i lable in fo ur dif f er en t e nd-to -e nd resist a n ce va l u es (5 k?, 10 k?, 50 k?, 100 k?), th es e lo w t e m p era t ur e co ef f i cien t de vices a r e i d e a l fo r hig h acc u rac y a n d s t ab i l i t y va r i a b le r e sis t a n c e ad j u stm e n t s. the wi p e r s e t t i n gs a r e co n t r o l l a b l e t h r o ug h t h e i 2 c co m p a t ib l e dig i t a l in t e r f ace , whic h can als o be us e d t o r e ad bac k t h e p r es en t w i p e r re g i ste r c o n t ro l word. t h e re s i st anc e b e t w e e n t h e w i p e r a nd ei t h er e nd p o in t o f t h e f i xe d r e sisto r va r i es lin e a r ly wi t h r e s p ect t o t h e digi tal co de tra n sf er r e d i n t o t h e rd a c 1 la t c h. o p era t ing f r o m a 2.7 v t o 5.5 v p o w e r s u p p l y a nd co n s u m in g 3 a al lo ws fo r us a g e in p o r t a b le b a t t er y-o p er a t e d a p plic a t io n s . func tio n a l block di agram i 2 c interface wiper register s d a scl gnd v dd a w 03875-0-001 b fi g u r e 1 . 1 no te : the te rms d i gital po te nti ometer, vr, and rda c are us ed inte rchange a bl y in this d o cume nt. 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 . s p ecificatio n s subj ec t to ch an 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 proper ty of th eir respectiv e co mpan ies. 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 .
ad5246 t a ble of conte n ts e l e t r ial c a r a t e r i s t is5 k? v e rsio n e l e tr ial c a r a t e r i s t is10 k?, 50 k?, 100 k? v e rsio n s 4 t i min g ca r a ter i s t is5 k?, 10 k?, 50 k?, 100 k? v e rsio n s 5 a b s o l t e m a im m r a t i n g s 6 t p i al p e r o r ma n e c a r a t e r i s t is t e st cir i t s 10 i 2 c i n ter ae 11 o p era t ion 12 p r og ra mmin g t e v a r i a b le resis t o r 12 i 2 c c o m p a t i b le 2- i r e s e r i al bs 1 l e e l s i t i n g o r b i ir e t io nal i n t e r ae 1 es d p r o t e t i on 1 t e r m inal v o l t a g e o p era t in g r a n g e 14 m a im m o p e r a t in g c r r en t 14 p o e r - u p s e en e 14 l a o t an p o er s p pl b p a s s in g 14 c o n s t a n t b i as to ret a in resis t an e s e t t in g 15 e al a t i o n b o a r 15 p i n c o n igra t io n an f n t i on d e s r i p t ion s 16 o t l in e dim e n s io n s 1 or er i n g g ie 1 revision history re i s i o n 0 i n i t ial v e r s i o n re 0 page 2 o 2 0
ad5246 electrical characteristics?5 k version table 1. v dd = 5 v 10% or 3 v 10%; v a = + v dd ; C40 c < t a < +12 5 c; unles s ot herwi s e not e d p a r a e t e r b o l c o n d i t i o n s m i n tp 1 m a n i t dc carac tr tcr t at md resistor dierential onlin earit 2 r d r wb C 1 . 5 0 . 1 + 1 . 5 b resistor ntegral onlinearit 2 r r wb C 4 0 . 7 5 + 4 b oinal resi sto r t o lerance 3 r ab t a = 25c C30 +30 % resistance te p erature coeicient r ab t wiper = o con n ect 45 ppc r wb r wb c o d e = 0 0 0 , v dd = 5 v 75 150 c o d e = 0 0 0 , v dd = 2.7 v 150 400 rtr trm a voltage range 4 v b, w d v dd v capacitance 5 b c b = 1 m, meas ured to d, code = 040 45 pf capacitance 5 w c w = 1 m, meas ured to d, code = 040 60 pf coonmode eaage cm 1 n a dta p t ad tp t nput ogic ig h v v dd = 5 v 2.4 v nput ogic ow v v dd = 5 v 0.8 v nput ogic ig h v v dd = 3 v 2.1 v nput ogic ow v v dd = 3 v 0.6 v nput current v = 0 v or 5 v 1 a nput capacitance 5 c 5 p f pwr pp power uppl range v dd ra 2 . 7 5 . 5 v uppl current dd v = 5 v or v = 0 v 3 8 a power dissi pati on 6 p d v = 5 v or v = 0 v, v dd = 5 v 40 w power uppl e nsitiit pr v dd = +5 v 10%, cod e = m i d s cale 0.01 0.02 %% damc c aractr t c 5, 7 bandwidth C3 db bw5 r ab = 5 , code = 040 1.2 m t o tal aronic distortion t d w v a = 1 v rs, v b = 0 v, = 1 0.05 % v w ettling tie t v a = 5 v, 1 b rror band 1 s resistor oise v o ltage densit e wb r wb = 2.5 , r = 0 6 nv 1 tpical s p eci ications repres e nt aera g e read ings at 25c and v dd = 5 v. 2 r e si st o r po si t i on n o n l i n ea ri t error r i s t h e dei a t i o n r o an ideal al u e eas ured betw een the aiu re si s t a n ce a n d t h e i n i u resi st a n ce wi per posi t i on s. r d e a s ure s t h e rela t i e st ep ch a n ge ro i d ea l bet w een succ essi e t a p posi t i on s . pa rt s a r e gua ra n t eed o n o t o n i c. 3 co de = 07f. 4 r e si st o r t e r i n a l s a a n d w h a e n o li i t a t i o n s on po la ri t wi t h respect t o e a ch ot h e r. 5 ua r a n t eed b des i gn a n d n o t sub ect t o pro d uct i on t e st . 6 p d i s ca lcula t e d r o dd v dd . cm l o gi c lee l i n put s resu lt in iniu power d i ss ipation. 7 al l d naic characteris t ics use v dd = 5 v. re. 0 page 3 o 2 0
ad5246 electrical characteristics?10 k, 50 k, 100 k versions table 2. v dd = 5 v 10% or 3 v 10%; v a = v dd ; C40c < t a < +125c ; u n l e ss otherwise noted p a r a e t e r b o l c o n d i t i o n s m i n tp 1 m a n i t dc carac tr tcr t at md resistor dierential onlin earit 2 r d r wb , v a = o connect C1 0.1 +1 b resistor ntegral onlinearit 2 r r wb , v a = o connect C2 0.25 +2 b oinal resi sto r t o lerance 3 r ab t a = 25c C20 +20 % resistance te p erature coeicient r ab t wiper = o con n ect 45 ppc r wb r wb c o d e = 0 0 0 , v dd = 5 v 75 150 c o d e = 0 0 0 , v dd = 2.7 v 150 400 rtr trm a voltage range 4 v b, w d v dd v capacitance 5 b c b = 1 m, meas ured to d, code = 040 45 pf capacitance 5 w c w = 1 m, easured to d, code = 040 60 pf coonmode eaage cm 1 n a dta p t ad tp t nput ogic ig h v v dd = 5 v 2.4 v nput ogic ow v v dd = 5 v 0.8 v nput ogic ig h v v dd = 3 v 2.1 v nput ogic ow v v dd = 3 v 0.6 v nput current v = 0 v or 5 v 1 a nput capacitance 5 c 5 p f pwr pp power uppl range v dd ra 2 . 7 5 . 5 v uppl current dd v = 5 v or v = 0 v 3 8 a power dissi pati on 6 p d v = 5 v or v = 0 v, v dd = 5 v 40 w power uppl e nsitiit pr v dd = +5 v 10%, cod e = m i d s cale 0.01 0.02 %% damc c aractr t c 5, 7 bandwidth C3 db bw r ab = 10 50 100 , code = 040 60010040 t o tal aronic distortion t d w v a =1 v rs, = 1 , r ab = 10 0.05 % v w ettling tie 10 50 100 t v a = 5 v 1 b rror band 2 s resistor oise v o ltage densit e wb r wb = 5 , r = 0 nv 1 tpical s p eci ications repres ent aera g e read ings at + 25c and v dd = 5 v. 2 r e si st o r po si t i on n o n l i n ea ri t error r i s t h e dei a t i o n r o an ideal al u e eas ured betw een the aiu re si s t a n ce a n d t h e i n i u resi st a n ce wi per posi t i on s. r d e a s ure s t h e rela t i e st ep ch a n ge ro i d ea l bet w een succ essi e t a p posi t i on s . pa rt s a r e gua ra n t eed o n o t o n i c. 3 co de = 07f. 4 r e si st o r t e r i n a l s a a n d w h a e n o li i t a t i o n s on po la ri t wi t h respect t o e a ch ot h e r. 5 ua r a n t eed b des i gn a n d n o t sub ect t o pro d uct i on t e st . 6 p d i s ca lcula t e d r o dd v dd . cm l o gi c lee l i n put s resu lt in iniu power d i ss ipation. 7 al l d naic characteris t ics use v dd = 5 v. re. 0 page 4 o 2 0
ad5246 timing characteristics?5 k, 10 k, 50 k, 100 k versions table 3. v dd = 5 v 10% or 3 v 10%; v a = v dd ; C40c < t a < +125c ; u n l e ss otherwise noted p a r a e t e r b o l c o n d i t i o n s m i n tp 1 ma n i t 2 c t rfac tm c arac tr t c 2, 3 peciications appl to all parts c cloc freu enc c 4 0 0 t b f bus free ti e between tp and tart t 1 1 . 3 s t d;ta old tie repeated ta r t t 2 ater this period, the irst cloc p u lse is g e n e r a t e d . 0 . 6 s t w ow period o c cloc t 3 1 . 3 s t igh period o c cloc t 4 0 . 6 5 0 s t ;t a e tup ti e or repeated tart condition t 5 0 . 6 s t d;dat data old tie t 6 0 . s t ;dat data etu p tie t 7 1 0 0 n s t f fall tie o both da and c ignals t 8 3 0 0 n s t r rise tie o both da and c ignals t 3 0 0 n s t ;t et u p ti e or tp condition t 10 0 . 6 s 1 tpical s p eci ications repres e nt aera g e read ings at 25c and v dd = 5 v. 2 ua r a n t eed b des i gn a n d n o t sub ect t o pro d uct i on t e st . 3 e e t i i n g d i a g r a s , figu , or locations o easu r ed alues. f i g u r e 2 5 r e 2 6 f i g u r e 2 7 re. 0 page 5 o 2 0
ad5246 absolute maximum ratings table 4. t a = 25c, u n less otherwise n o ted 1 p a r a e t e r v a l u e v dd to d C0.3 v to +7 v v a , v w to d v dd terinal current, aCb, aCw, bCw pulsed 2 2 0 a c o n t i n u o u s 5 a digital nputs and utput voltage to d 0 v to v dd + 0.3 v perating te p erature range C40c to +125c maiu unction teperature t ma 1 5 0 c torage teperature C65c to +150c ead teperature oldering, 10 sec 300c t h eral resista n ce 3 a c706 340cw 1 t re sse s a b o e t h o se li st e d un d e r abs o lut e ma i u r a t i n gs a ca use peranent d aage to the d e ice. this is a s t ress rating onl ; unctional o p e r atio n o the deice at the s e o r an o the r co nd itio ns a b o e tho se i n di ca t e d i n t h e op era t i o n a l sect i o n o this s p eci ication is not ipl i ed . pos ure t o a b s o lu t e a iu rating co nd itio ns o r e tend e d pe riod s a a e ct d e ice rel iabil it. 2 maiu terinal current is bounde d b the aiu c urrent handling o the s w itches , ai u power d i ss ip ation o the pacage, and aiu appl ied ol t age acros s an two o the a , b, and w terinal s at a gien resi st a n ce. 3 pa ca g e pow e r di s s i p a t i o n = t m a C t a a . d cat d electrostatic discharge sensitie deice. le c tros tatic charg e s as high as 4000 v readil accuulate on the huan bod and test e uipent and can discharge wi thout detection. although this product eatures proprietar d protection circu i tr, peranent daa ge a occur on deices subected to high energ electrostatic discharges. there ore, prop er d precautions a r e recoended to aoid peror a nce degradation or l o ss o unctiona l it. re. 0 page 6 o 2 0
ad5246 typical perf orm ance cha r acte ristics code (decimal) rhe os tat mode inl (ls b ) 0 1.0 0 0.2 1.0 16 32 48 64 80 96 112 128 0.8 0.6 0.4 0.2 0.4 0.6 0.8 v dd = 2.7v v dd = 5.5v t a = 25 c r ab = 10k ? ? ? rev. 0 | page 7 of 2 0
ad5246 temperature ( c ) i dd, s u p p l y curre nt ( ? rev. 0 | page 8 of 2 0
ad5246 10k 6 1 2 1 8 2 4 0 6 0 4 2 5 4 100k 1m 10m 6 0 5k ? ? ? ? ? ? ? ? ?
ad5246 test circuits fi g r e 2 0 to e i ne t e te st o n i t i o ns s e i n t e p r o t s p e i ia t io n t a b l es fi g r e 2 4 085-0-004 i v ms b dut f i gre 20 t e s t c i r it or r e s i s t or p o s i tion non l i n e a r i t e rror r eo s ta t o p er a t ion r - inl, r - dnl 085-0-00 ? ? ? ? ? ?
ad5246 i 2 c interface table 5. write mode s 0 1 0 1 1 1 0 w a x d 6 d 5 d 4 d 3 d 2 d 1 d 0 a p slave address byte data byte table 6. r e ad mode s 0 1 0 1 1 1 0 r a 0 d 6 d 5 d 4 d 3 d 2 d 1 d 0 a p slave address byte data byte s = s t a r t c o n d i t io n. p = s t o p c o n d i t io n. a = a c k n o w le dge . x = d o n t c a r e . w = w r i t e . r = re ad . d6, d5, d4, d3, d2, d1, d0 = d a t a bi ts. t 1 t 3 t 4 t 2 t 7 t 8 t 9 ps p s t 10 t 5 t 9 t 8 scl sda t 2 t 6 03875-0-019 f i g u re 25. i 2 c inter f a c e , detai l ed t i m i ng di a g r a m scl frame 1 frame 2 start b master ac b ad5246 slave address bte stop b master data bte sda 0 1 0 1 1 1 0 r/w xd 6 d 4 d 3 d 2 d 1 d 0 1 19 ac b ad5246 1 9 d5 03875-0-014 f i g u re 26. w r it ing t o t h e r d a c r e g i s t e r no ac b master scl sda 0 1 0 1 1 1 0 r/w 0 d 6d 5 d 4d 3 d 2d 1 d 0 1 9 1 9 frame 1 frame 2 start b master ac b ad5246 slave address bte rdac register stop b master 03875-0-013 f i gur e 2 7 . re a d i n g fr om the rd a c regi st e r rev. 0 page 11 of 20
ad5246 rev. 0 | page 12 of 20 operation the ad5246 is a 128-position, digitally controlled variable resistor (vr) device. an internal power-on preset places the wiper at midscale during power-on, which simplifies the default condition recovery at power-up. programming the variable resistor rheostat operation the nominal resistance of the rdac between terminals a and b is available in 5 k?, 10 k?, 50 k?, and 100 k?. the final two or three digits of the part number determine the nominal resistance value, e.g., 10 k? = 10, 50 k? = 50. the nominal resistance (r ab ) of the vr has 128 contact points accessed by the wiper terminal, plus the b terminal contact. the 7-bit data in the rdac latch is decoded to select one of the 128 possible settings. assuming a 10 k? part is used, the wipers first connection starts at the b terminal for data 0x00. since there is a 50 ? wiper contact resistance, such a connection yields a minimum of 100 ? (2 50 ?) resistance between terminals w and b. the second connection is the first tap point, which corresponds to 178 ? (r wb = r ab /128 + r w = 78 ? + 2 50 ?) for data 0x01. the third connection is the next tap point, representing 256 ? (2 78 ? + 2 50 ?) for data 0x02, and so on. each lsb data value increase moves the wiper up the resistor ladder until the last tap point is reached at 10,100 ? (r ab + 2 r w ). figure 28 shows a simplified diagram of the equivalent rdac circuit. bx wx ax d6 d4 d5 d2 d3 d1 d0 rdac latch and decoder r s r s r s 03875-0-015 figure 28. ad5246 equivalent rdac circuit the general equation determining the digitally programmed output resistance between w and b is w ab wb r r d d r + = 2 128 ) ( (1) where d is the decimal equivalent of the binary code loaded in the 7-bit rdac register, r ab is the end-to-end resistance, and r w is the wiper resistance contributed by the on resistance of the internal switch. in summary, if r ab = 10 k? and the a terminal is open-circuited, the output resistance r wb shown in table 7 will be set for the indicated rdac latch codes. table 7. codes and corresponding r wb resistance d (dec.) r wb (?) output state 127 10,100 full scale (r ab + 2 r w ) 64 5,100 midscale 1 178 1 lsb 0 100 zero scale (wiper contact resistance) note that in the zero-scale condition, a finite wiper resistance of 100 ? is present. care should be taken to limit the current flow between w and b in this state to a maximum pulse current of no more than 20 ma. otherwise, degradation or possible destruction of the internal switch contact can occur. typical device-to-device matching is process lot dependent and may vary by up to 30%. since the resistance element is processed in thin film technology, the change in r ab with temperature has a very low 45 ppm/c temperature coefficient.
ad5246 i 2 c compatible 2-wire serial bus the f i rs t b y t e o f th e ad5246 is a s l a v e addr es s b y t e (s ee a n d ) . i t has a 7- b i t sl a v e addr ess and a r/ w bit . t h e s e v e n ms bs o f t h e sla v e addr es s a r e 0101110 f o llo w e d b y 0 f o r a wr i t e co mmand o r 1 t o place t h e de vic e in r e ad m o de . t a b l e 5 a b l e 5 t a b l e 6 the 2- wir e i 2 c s e r i a l bu s proto c o l op e r a t e s a s f o l l ow 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 ion, w h ich is w h e n a h i g h -t o-lo w t r a n s i t i o n o n t h e s d a line o c c u rs while scl is hig h (s e e ). th e fol l o w in g b y t e i s t h e sla ve addr es s b y t e , w h ich co n s is ts o f t h e 7- b i t sla ve addr es s fol l o w e d b y a n r/ w bi t ( t h i s bi t de te r m i n e s w h e t he r da t a w i l l b e re a d f r om or w r i t te n to t h e sla ve de v i ce ). f i gur e 2 6 f i gur e 2 6 the s l a v e w h os e addr es s co r r esp o n d s t o t h e t r an smi t t e d addr es s r e s p onds b y p u l l in g t h e s d a l i n e lo w d u r i n g t h e nin t h clo c k p u ls e (t his is t e r m e d t h e ack n o w le d g e b i t). a t th i s s t a g e , all o t h e r devi ce s o n t h e b u s r e m a in idle wh ile t h e s e l e c t e d d e v i c e w a i t s for da t a to b e w r it te n to or re a d f r om i t s s e r i a l r e g i s t er . i f t h e r/ w b i t is hig h , t h e mas t er wi l l r e ad f r o m t h e sla ve de v i ce . on t h e o t h e r hand , if t h e r/ w bit i s lo w , t h e mast er wi l l wr i t e t o t h e s l a ve de vi ce . 2. i n wr i t e m o de , a f t e r ack n o w le dgem e n t o f t h e s l a v e addr es s b y te, t h e ne x t by te i s t h e d a t a by te. d a t a i s t r ans m i tte d ove r th e s e r i al b u s in s e q u en ces o f nin e c l o c k p u ls es (eig h t da ta bi t s f o l l ow e d by a n a c k n ow l e d g e bi t ) . t h e t r a n s i t i on s o n th e s d a line m u s t o c c u r d u r i ng th e lo w p e r i o d o f scl an d r e ma in sta b le d u r i n g th e hig h p e r i o d o f scl (s e e t ) . 3. i n r e ad mo de, af ter ack n o w le dg m e n t o f t h e sl a ve addr ess b y t e , da t a is r e cei v ed o v er the s e r i al b u s in s e q u en ces o f ni n e clo c k p u ls e s (a s l ig h t dif f er en c e f r o m t h e w r i t e m o de w h er e eig h t da t a b i ts a r e fol l o w e d b y a n ack n o w le dge b i t). s i m i la r l y , th e tra n s i ti o n s o n t h e s d a lin e m u s t occur d u ri n g th e l o w pe ri od o f s c l a n d r e m a in s t a b l e d u ri n g th e hig h p e r i o d o f scl (s e e ) . f i gur e 2 7 f i gur e 2 7 4. w h en al l da ta b i ts ha v e been r e ad o r wr i t t e n, a s t o p co ndi t ion is est a b l ish e d b y t h e mast er . a s t op co n d i t ion is def i n e d as a lo w-to -hig h t r a n s i t i o n o n t h e sd a l i ne w h i l e scl is hig h . i n wr i t e mo de , t h e mas t er wi l l p u l l t h e sd a lin e hig h d u r i n g t h e t e n t h clo c k p u ls e t o est a b l ish a st op co ndi t ion (s e e ) . i n r e ad m o de , t h e mas t er wil l is s u e a n o a c k n o w le dge fo r t h e nin t h clo c k p u ls e (i .e ., t h e s d a li ne r e ma i n s hig h ). the mas t er wi l l t h en b r in g t h e s d a li ne lo w b e fo r e t h e t e n t h cl o c k p u ls e, w h ich go es hig h t o es ta b l ish a s t o p co n d i t ion (s e e ) . a r e p e a t e d wr i t e f u n c t i on g i v e s t h e us er f l exi b i l i t y t o u p da te t h e rd a c o u t p ut a n u m b er o f t i m e s a f t e r addr es si ng t h e p a r t o n l y o n ce . f o r exa m ple , a f t e r t h e r d a c has ack n o w l e dge d i t s s l a v e addr es s i n wr i t e m o de , t h e rd a c o u t p ut wi l l up da te o n e a ch s u cces s i v e b y te . i f dif f er en t in st r u c t io n s a r e ne e d e d , wr i t e / r e ad m o d e has t o st ar t a g a i n wi t h a ne w sla ve ad dr ess an d d a t a b y t e . s i mil a rl y , a r e p e a t e d r e ad f u n c tio n o f th e rd a c is als o al lo w e d . level shifting for bidirectional interface w h i l e m o s t legac y sys t em s ma y b e o p era t e d a t on e v o l t a g e , a n e w co m p o n en t m a y b e o p ti mized a t a n o t h e r . w h e n t w o sys t em s o p era t e t h e s a me sig n al a t t w o dif f er en t v o l t a g es, p r o p e r le v e l shif t i ng is n e e d e d . f o r in st a n c e , o n e can us e a 3.3 v e 2 pro m to i n te r f a c e w i t h a 5 v di g i t a l p o te n t i o me te r . a l e v e l shif t i ng s c h e m e is n e e d e d t o en a b le a b i dir e c t iona l co mm u n i- ca ti o n so th a t th e se t t i n g o f th e d i gi t a l po t e n t i o m e t e r ca n b e sto r e d to and r e t r ie ve d f r o m t h e e 2 p r o m . f s h o w s one o f th e im p l e m en ta ti o n s . m1 a n d m2 ca n be a n y n c h a n n e l sig n al fet s , o r if v dd falls be lo w 2.5 v , m1 an d m2 ca n be lo w thr e s h old fet s s u c h as t h e f d v301n. i g u r e 2 9 f i gure 29. l e vel s h if ting for o p e r at ion at d i ffe r e nt p o te ntials e 2 prom ad5246 sda1 scl1 d g r p r p 3.3v 5v s m1 scl2 sda2 r p r p g s m2 v dd1 = 3.3v v dd2 = 5v d 03875-0-011 esd protection a l l dig i t a l in pu t s a r e p r o t e c te d wi t h a s e r i es in pu t r e sisto r a n d p a ralle l z e n e r e s d s t r u ct ur es sh o w n in f a n d . this a p plies t o t h e dig i t a l in p u t p i n s sd a and s c l. i gur e 3 0 f i g u re 30. e s d pr ot ec t i o n of d i g i t a l p i ns f i gur e 3 1 f i g u re 31. e s d pr ot ec t i o n of r e s i s t o r t e r m in als logic 340 ? rev. 0 | page 13 of 20
ad5246 terminal voltage operating ra nge the ad5246 v dd a n d g n d p o w e r su p p ly def i n e s t h e b o u n dar y c o ndi t i o ns for prop e r 3 - te r m i n a l di g i t a l p o te n t i o me te r o p era t ion. s u p p l y sig n als p r es en t o n t e r m inals b a n d w t h a t e x ceed v dd o r gnd wi l l b e clam p e d b y t h e in ter n al fo r w a r d b i as e d dio d es (s e e ) . f i gur e 3 2 f i g u re 32. m a x i mu m t e r m i n a l v o lt ag es s e t by v dd and g n d i gur e 3 2 b v dd w gnd 03875-0-016 maximum operating current a t lo w co de val u es, t h e us er s h o u ld b e a w a r e t h a t d u e t o lo w r e sis t a n c e val u e s , t h e c u r r en t t h r o ug h t h e rd a c ma y exce e d th e 5 ma limi t. i n f , a 5 v s u p p l y is p l ac ed o n t h e wi p e r , a n d t h e c u r r en t t h r o ug h ter m in a l s w an d b is plo t te d w i t h r e sp e c t to co d e . a line is a l s o dr a w n d e no t i n g t h e 5 ma c u r r en t limi t. n o t e tha t a t lo w co de va l u es (p a r tic u la rl y fo r th e 5 k and 10 k o p t i o n s), t h e c u r r en t le vel in cr e a s e s sig n i f ica n t l y . c a r e sh o u ld b e t a k e n t o limi t t h e c u r r en t f l o w b e twe e n w and b i n t h is st a t e to a m a x i m u m con t i n uo us c u r r en t o f 5 ma and a max i m u m p u ls e c u r r en t o f n o m o r e t h an 20 m a . o t h e r w is e, deg r ad a t ion o r p o ssi b le de st r u c t io n o f t h e in t e r n a l sw i t ch co n t ac ts can o c c u r . i gur e 3 3 f i g u re 33. m a x i mu m o p e r at ing cur r e n t code (decimal) iwb curre nt (ma) 0 0.01 0.10 1.00 10.00 16 32 48 64 80 96 112 128 100.00 03875-0-034 5ma current limit r ab = 5k ? ? ? ? power-up sequence sin c e t h e es d pr o t e c t i o n di o d e s limi t t h e v o l t age co m p l i an ce a t t e r m ina l s b an d w (s e e f ), i t is im p o r t an t t o p o w e r v dd /gn d bef o r e a p p l yin g a n y vo l t a g e t o t e r m inals b a n d w ; o t h e r w is e , t h e dio d e wi l l b e fo r w a r d b i as e d s u ch t h a t v dd wi l l b e p o w e r e d uni n t e n t io nal l y an d ma y a f fe c t t h e r e s t o f t h e us er s cir c ui t. t h e id e a l p o w e r - u p s e q u en c e is in t h e fol l o w in g o r der : gnd , v dd , d i g i t a l i n p u t s , a n d t h e n v b /v w . t h e rel a t i ve ord e r of po w e ri n g v b an d v w an d t h e di g i t a l i n p u ts is no t im p o r t a n t as l o ng a s t h e y are p o we re d af te r v dd /gnd . layout and power supply b y passing i t is a go o d p r ac t i ce t o em plo y a co m p ac t, mi ni m u m le a d -len gt h la yo u t desig n . th e le ads t o th e in p u ts sh o u ld be as dir e c t as pos s i b le wi th a m i n i m u m co n d uct o r le n g th . g r o u n d p a th s s h o u ld ha v e lo w r e sis t a n ce an d l o w ind u c t an ce . s i mil a rl y , i t is a g o o d p r ac tic e to b y p a s s th e p o w e r s u p p lies wi t h qu a l it y c a p a c i tors for opt i m u m st abi l it y . supply l e a d s to t h e de vice s h o u l d b e b y p a s s e d wi th 0.01 f t o 0.1 f dis c o r c h i p cera mic c a p a ci to rs. l o w es r 1 f t o 10 f ta n t al um o r e l ec tr ol ytic ca p a ci t o rs sh o u ld als o be a p p l ied a t t h e su p p lies t o mini mi ze an y t r a n sien t dist ur b a n c e an d lo w f r e q uen c y r i p p le (s e e ) . n o t e tha t t h e dig i tal g r o u nd sho u ld als o be j o i n e d re motely to t h e an a l o g g r ou nd a t one p o i n t to mi ni m i z e th e gr o u n d bo un ce . f i gur e 3 4 f i g u r e 3 4 . p o w e r su pp l y by pa s s i n g ad5246 v dd c1 c3 gnd 10 rev. 0 | page 14 of 20
ad5246 rev. 0 | page 15 of 20 constant bias to retain resistance setting for users who desire nonvolatility but cannot justify the addi- tional cost for the eemem, the ad5246 may be considered as a low cost alternative by maintaining a constant bias to retain the wiper setting. the ad5246 was designed specifically with low power in mind, which allows low power consumption even in battery-operated systems. the graph in figure 35 demonstrates the power consumption from a 3.4 v 450 mahr li-ion cell phone battery, which is connected to the ad5246. the measure- ment over time shows that the device draws approximately 1.3 a and consumes negligible power. over a course of 30 days, the battery was depleted by less than 2%, the majority of which is due to the intrinsic leakage current of the battery itself. days battery life depleted 0 90% 92% 94% 96% 51015 98% 100% 102% 104% 106% 108% 110% 20 25 30 03875-0-035 t a = 25 c figure 35. battery operating life depletion this demonstrates that constantly biasing the pot is not an impractical approach. most portable devices do not require the removal of batteries for the purpose of charging. although the resistance setting of the ad5246 will be lost when the battery needs replacement, such events occur rather infrequently such that this inconvenience is justified by the lower cost and smaller size offered by the ad5246. if and when total power is lost, the user should be provided with a means to adjust the setting accordingly. evaluation board an evaluation board, along with all necessary software, is available to program the ad5246 from any pc running windows? 98, windows 2000, or windows xp?. the graphical user interface, as shown in figure 36 is straightforward and easy to use. more detailed information is available in the user manual, which comes with the board. 03876-0-061 figure 36. ad5246 evaluation board software
ad5246 pin conf iguration and fu nction descriptions 1 2 3 6 5 4 v dd gnd scl ad5246 top view (not to scale) b w sd a 03875-0-018 f i g u re 37. p i n f u n c t i on d e s c ript io ns, 6-l e ad sc 7 0 ta ble 8. a d 52 46 pi n f u nct i o n d e s c ri pt i o ns pin no. mnemonic description 1 v dd positive power s u pply. 2 g n d d i g i t a l g r o u n d . 3 s c l serial clock input. positive edg e triggered. 4 sda serial data inpu t/ output. 5 w w t e r m i n a l . 6 b b t e r m i n a l . rev. 0 | page 16 of 20
ad5246 outline dimensions 0. 2 2 0. 0 8 0. 46 0. 36 0. 26 8 4 0 0. 3 0 0. 1 5 1. 00 0. 90 0. 70 sea t i n g p l ane 1. 10 m a 3 5 4 2 6 1 2. 0 0 bs c pin 1 2. 10 bs c 0. 6 5 bs c 1. 25 bs c 1. 3 0 bs c 0. 10 m a 0.10 coplanarit compliant to edec standards mo-203ab f i g u re 38. 6-l e ad t h in s h ri nk s m a ll o u t lin e t r ans i s t o r [ s c70] (k s-6) di me nsio ns sho w n i n mi ll im e t e r s ordering guide m o d e l r ab (k?) temperature r a nge package descri ption package option branding ad5246bks5-r2 5 C40c to +125c 6-lead sc70 ks-6 d16 ad5246bks5-rl 7 5 C40c to +125c 6-lead sc70 ks-6 d16 ad5246bks10-r2 10 C40c to +125c 6-lead sc70 ks-6 d1d ad5246bks10-rl7 10 C40c to +125c 6-lead sc70 ks-6 d1d ad5246bks50-r2 50 C40c to +125c 6-lead sc70 ks-6 d1c ad5246bks50-rl7 50 C40c to +125c 6-lead sc70 ks-6 d1c AD5246BKS100-R2 100 C40c to +125c 6-lead sc70 ks-6 d1a ad5246bks100-rl7 100 C40c to +125c 6-lead sc70 ks-6 d1a ad5246eval see note 1 evaluation boar d 1 th e eval uat i on board is s h ippe d with the 10 k ? r ab re si st or opt i on ; h o w e ver, t h e boa r d i s com p a t i b le wi t h a ll a v a i l a b le r e si st or va lu e opt i on s. rev. 0 | page 17 of 20
ad5246 notes rev. 0 | page 18 of 20
ad5246 notes rev. 0 | page 19 of 20
ad5246 notes pur c has e o f licen s e d i 2 c co m p on e n ts o f analog d e vices o r on e o f i t s s u b l i c en s e d a s s o c i a t e d c o m p a n ies con v e y s a licen s e fo r t h e p u r c haser un der th e p h ili p s i 2 c p a t e n t r i g h ts to us e t h es e com p o n e n ts in an i 2 c sys t em, p r o v i d e d t h a t t h e syst em co nfo r m s to t h e i 2 c s t a n da rd s p e c if ica t ion as def i ne d b y phi l i p s. ? 2003 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 . c03875C0 C 9/03(0) rev. 0 | page 20 of 20

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