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zero drift, bidirectional current shunt monitor data sheet ad8218 rev. b document feedback information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties that may re sult from its use. specifications subject to change without notice. no license is granted by implication or otherwise under any patent or patent rights of analog devices. trademarks and registered trademarks are the property of their respective owners. one technology way, p.o. box 9106, norwood, ma 02062 - 9106, u.s.a. tel: 781.329.4700 ? 2011C 2013 analog devices, inc. all rights reserved. techni cal support www.analog.com features high common - mode voltage range 4 v to 80 v operating ? 0 .3 v to + 85 v survival buffered output voltage gain = 20 v/v wide operating temperature range : ? 40c to +125c exce llent ac and dc performance 1 00 n v/c typical offset drift 50 v typical of fset 5 ppm/c typical gain drift 1 1 0 d b typical cmrr at dc applications high - side current sensing 48 v t elecom power m anagement base s tations bidirectional motor control precision high voltage current sources functional block dia gram ldo r2 r1 ad8218 r4 r3 +in ?in out enb ref gnd v s 09592-001 figure 1 . general description the ad8218 is a high voltage, high resolution current shunt amplifier. it features a set ga in of 20 v/v, with a maximum 0.3 5 % gain error over the entire temperature range. the buffered output voltage directly inter faces with any typical converter. the ad8218 offers excellent input common - mode rejection from 4 v to 80 v . the ad8218 performs bidirectional current measurements across a shunt resistor in a variety of industrial and telecom applications , including motor control, battery management, and base statio n power amplifier bias control. the ad8218 offers breakthrough performance throughout the ? 40 c to + 125 c temperature range. it features a zero - drift core, which leads to a typical offset drift of 1 00 nv/ c throughout the operating temperature range and the common - mode voltage range. special attention is devoted to output linearity being maint ained throughout the input differential voltage range of 0 mv to ~ 250 mv . the ad8218 also includes an internal 80 mv reference that can be enabled for optimal dynamic range in unidirectional current sense applications . t he typical input offset voltage is 50 v. the ad8218 is offered in an 8 - l ead msop package and an 8 - lead lfcsp package .
ad8218 data sheet rev. b | page 2 of 16 table of contents features .............................................................................................. 1 applications ....................................................................................... 1 functional block diagram .............................................................. 1 general description ......................................................................... 1 revision hist ory ............................................................................... 2 specifications ..................................................................................... 3 absolute maximum ratings ............................................................ 4 esd caution .................................................................................. 4 pin configurations and function descriptions ........................... 5 typical performance characteristics ............................................. 6 theory of operation ...................................................................... 10 amplifier core ............................................................................ 10 output clamping ....................................................................... 10 application notes ........................................................................... 11 supply (v s ) connections ........................................................... 11 enable pin (enb) operation .................................................... 11 applications information .............................................................. 12 unidirectional high - side current sensing ............................ 12 bidirectional high - side c urrent sensing ............................... 12 motor control current sensing ............................................... 12 outline dimensions ....................................................................... 13 ordering guide .......................................................................... 13 revision history 4/13 rev. a to rev. b added 8 - lead lfcsp ......................................................... universal changes to general description section ...................................... 1 added figure 3, renumbered sequentially .................................. 5 change s to tabl e 3 ............................................................................ 5 added figure 3 7 .............................................................................. 13 upd ated outline dimensions ....................................................... 13 changes to ordering guide .......................................................... 13 2/11 rev. 0 to rev. a changes to features .......................................................................... 1 1/1 1 revision 0 : initial version
data sheet ad8218 rev. b | page 3 of 16 specifications t opr = ? 40 c to +125 c, t a = 25 c, r l = 25 k ? (r l is the output load resistor) , input common - mode voltage (v cm ) = 4 v , unless otherwise noted . table 1. parameter min typ max unit test conditions /comments gain initial 20 v/v accuracy 0.1 % v o 0.1 v dc, t a accuracy o ver temperature 0.3 5 % t opr gain vs. temperature 5 ppm/ c t opr voltage offset offset voltage (rti 1 ) 2 00 v 25c over temperature (rti 1 ) 300 v t opr offset drift 1 00 n v/ c t opr input bias current 2 130 a t a , input common mode = 4 v, v s = 4 v 220 a t opr , input common mode = 4 v, v s = 4 v common - mode input voltage range 4 80 v common - mode continuous differential input voltage range 3 0 250 mv differential input voltage common - mode rejection (cmrr) 9 0 110 db t opr output output voltage range low 0.01 v output voltage range high v s ? 0.1 v t a output impedance 2 ? internal reference (enb pin connected to gnd) initial value 80 mv voltage at out with a differential input of 0 v and a common - m ode inpu t of 4 v offset (rti 1 ) ? 150 +150 v offset drift (rto 4 ) 10 v/ c v s = nc or v s = 5 v reference input (ref, pin 7) input impedance 1.5 m? input current 3 60 a dependent on v ref /1.5 m ? in put voltage range 0 5 v enb not connected to gnd input - to- output gain 1 0.0001 v/v dynamic response small - signal ?3 db bandwidth 4 50 khz slew rate 1 v/s noise 0.1 hz to 10 hz (rti 1 ) 2.3 v p - p spectral density, 1 khz (rti 1 ) 110 nv/ hz power supply operating range (pin 2 floating) 4 80 v power regulated from common mode , v s pin floating v s range (pin 2) 4 5.5 v v s m ust be less than 5.5 v if standalone supply is used quiescent current over temper a ture 800 a throughout input common mode power supply rejection ratio (psrr) 9 0 110 db t opr temperature range for specified performance ?40 +125 c 1 rti = referred to input. 2 refer to figure 9 for more information on the input bias current. this current varies based on the input common - mode voltage. t he i nput bias current flowing to the +in pin is also the supply current to the internal ldo. 3 the differential input voltage is specified as 250 mv because the output is internally clamped to 5 .2 v. this ensures that the output voltage does not exceed the ty pical adc input range, preventing damage. th e ad8218 can survive up to 5 v differentially but will only amplify ~250 mv correctly due to the output clamping function. 4 rto = referred to output.
ad8218 data sheet rev. b | page 4 of 16 absolute maximum ratings table 2. parameter rating max imum input voltage ( +in, ? in to gnd) ? 0.3 v to + 85 v differential input voltage (+in to C in) 5 v human body m odel ( hbm ) esd rating 2000 v operating temperature range (t opr ) ?40 c to +125c storage temperature range ?65c to +150c output short - circuit duration indefinite stresses above those listed under absolute maximum ratings may cause permanent damage to the device. this is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. esd caution
data sheet ad8218 rev. b | page 5 of 16 pin c onfiguration s and function descrip tions +in 1 v s 2 enb 3 gnd 4 ?in 8 ref 7 nc 6 out 5 nc = no connect. do not connect to this pin. ad8218 top view (not to scale) 09592-002 figure 2 . msop pin configuration 09592-103 notes 1. nc = no connec t . do not connect t o this pin. 2. the exposed p ad needs t o be connected t o pin 4 (gnd). 3 enb 4 gnd 1 +in 2 v s 6 nc 5 out 8 ?in 7 ref ad8218 t o p view (not to scale) figure 3 . lfcsp pin configuration table 3 . pin function descriptions pin o. neonic description 1 +in noni nverting input. 2 v s supply pin . bypass with a standard 0.1 f c ap acitor . 3 enb enable. connect to gnd to enable the internal 80 mv reference. 4 gnd ground. 5 out output. 6 nc no connect. do not connect to this pin. 7 ref reference inpu t . connect to a low impedance voltage. 8 ? in inverting input . epad exposed pad. the exposed pad needs to be connected to pin 4 (gnd). applies to lfcs p only.
ad8218 data sheet rev. b | page 6 of 16 typical performance characteri s tics 24 26 28 30 32 34 36 38 40 ?40 ?20 0 20 40 60 80 100 120 140 temper a ture (c) v osi (v) 09592-003 figure 4 . typical input off set vs. temperature 50 60 70 80 90 100 1 10 120 130 140 100 1000 10k 100k 1m frequenc y (hz) cmrr (db) ?40c +25c +125c 09592-004 figure 5 . typical cmrr vs. frequency 100 150 200 250 300 350 400 450 500 ?40 ?20 0 20 40 60 80 100 120 temper a ture (c) gain error (ppm) 09592-005 figure 6 . typical gain error vs. temperature 0 3 6 9 12 15 18 21 24 27 30 1k 10k 100k 1m frequenc y (hz) magnitude (db) 09592-006 figure 7 . typical smal l - signal bandwidth (v out = 200 mv p - p) ?5 ?4 ?3 ?2 ?1 0 1 2 3 4 5 6 7 8 9 10 0 5 10 15 20 25 30 35 40 45 50 t ot al output error (%) differentia l input (mv) 09592-007 fi gure 8 . total output error vs. differential input voltage 0 100 200 300 400 500 600 700 800 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 input common-mode vo lt age (v) input bias current (a) +in ?in 09592-008 figure 9 . input bias current vs. input common - mode voltage (differential input voltage = 5 mv , v s = nc )
data sheet ad8218 rev. b | page 7 of 16 200 250 300 350 400 450 500 ?40 ?20 0 20 40 60 80 100 120 supp l y current (a) temper a ture (c) 09592-109 figure 10 . supply current vs. temperature (v s = 5 v , v cm = 12 v) input output 5mv/div 1s/div 100mv/div 09592-009 figure 11 . rise time (differential input = 10 mv) input output 100mv/div 2v/div 5s/div 09592-010 figure 12 . rise time (differential input = 200 mv) input output 5mv/div 100mv/div 1s/div 09592-0 1 1 figure 13 . fal l time (differential input = 10 mv) input output 100mv/div 2v/div 5s/div 09592-012 figure 14 . fall time (differential input = 200 mv) input output 200mv/div 2v/div 5s/div 09592-013 figure 15 . differential overload recovery , rising
ad8218 data sheet rev. b | page 8 of 16 input output 200mv/div 2v/div 5s/div 09592-014 figure 16 . differential overload recovery , falling 79.0 79.5 80.0 80.5 81.0 81.5 82.0 ?40 ?20 0 20 40 60 80 100 120 reference r t o (mv) temper a ture (c) 09592- 1 16 figure 17 . internal reference voltage vs. temperature (v s = 5 v, v s = nc, v cm = 12 v , pin 1 (+in) and pin 8 (?in) shorted , pin 3 (enb) shorted to pin 4 ( gnd ) ) 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 1 1.0 1 1.5 12.0 ?40 ?30 ?20 ?10 0 10 20 30 40 50 60 70 80 90 100 1 10 120 temper a ture (c) maximum output sink current (ma) 09592-015 figure 18 . maximum output sink current vs. temperature 5.0 5.5 4.0 4.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 ?40 ?30 ?20 ?10 0 10 20 30 40 50 60 70 80 90 100 1 10 120 130 140 150 temper a ture (c) maximum output source current (ma) 09592-016 figure 19 . maximum output source current vs. temperature 4.900 4.910 4.920 4.930 4.940 4.950 4.960 4.970 4.980 4.990 5.000 5.010 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 output source current (ma) output vo lt age swing from rai l (v) 09592-017 figure 20 . output voltage swing fro m rail vs. output source current 0 50 100 150 200 250 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 output sink current (ma) output vo lt age range from gnd (v) 09592-018 figure 21 . output voltage range from gnd vs. output sink current
data sheet ad8218 rev. b | page 9 of 16 input output 50v/div 1v/div 500ns/div 09592-019 figure 22 . common - mode step r esponse , rising input output 50v/div 1v/div 1s/div 09592-020 figure 23 . common - mode step response, falling 180 90 120 150 30 60 0 ?200 ?100 0 100 200 09592-021 count v osi (v) figure 24 . input offs et distribution 500 300 400 100 200 0 ?4 ?2 0 2 4 09592-022 count gain drift (ppm/c) 1 3 ?1 ?3 figure 25 . gain drift distribution 140 80 100 120 20 60 0 ?0.6 ?0.4 0 0.2 0.6 09592-023 count offset drift (v/c) 40 0.4 ?0.2 figure 26 . input offset drift distribution 150 200 250 50 100 0 ?5 0 5 10 15 09592-024 count internal ref offset drift (v/c) figure 27 . internal ref offset drift distribution , referred to output (rto )
ad8218 data sheet rev. b | page 10 of 16 theory of o peration amplifier core in typical applications, the ad8218 amplifies a small differential input voltage generated by the load current flowing through a shunt resistor. the ad8218 rejects high common - mode vol - tages (up to 80 v) and provide s a ground - referenced , buffered output . figure 28 shows a simplified schematic of the ad8218 . v ref load v 2 i load v 1 shunt 4v to 80v i charge gnd 5v ldo r2 r1 ad8218 r4 r3 +in ?in out enb ref gnd v s c f 09592-027 figure 28 . simplified schematic the ad8218 is configured as a difference amplifier. the transfer function i s out = ( ( r 4 / r1 ) ( v 1 ? v 2 ) ) + v ref resistors r4 and r1 are matched to within 0.01% and have values of 1.5 m ? and 7 5 k? , respectively, meaning an input - to - output total gain of 20 v/v for the ad8218 . the difference between v 1 and v 2 is the voltage across the shunt resistor , or v in . therefore, the input - to - output transfer function of the ad8218 is out (v) = (20 v in ) + v ref th e ad8218 accurately amplifies the input differential signal, reje cting high voltage common modes ranging from 4 v to 80 v. the m ain amplifier uses a nove l zero - drift architecture, provi ding the end user with breakthrough temperature stability. the offset drift is typically less than 1 00 nv/c. th is performance leads to optimal accuracy and dynamic range. output clamping after the input common - mode voltag e in the application is above 5.2 v, the internal ldo output of the ad821 8 also reaches its maximum value of 5.2 v, which is the maximum output range of the ad821 8 . because in typical applications the output interfaces with a converter, clamping the ad821 8 output voltage to 5.2 v ensures that the adc input is not damaged due to excessive overvoltage.
data sheet ad8218 rev. b | page 11 of 16 application notes supply (v s ) connections the ad8218 includes an internal ldo , which allows the user to leave the v s pin floating , p ower ing the ad8218 d i rectly from the voltage present at pin 1 (+in) , provided this voltage is in the 4 v to 80 v range. a typical connection for the part in this configuration is shown in figure 29. +in i load v s shunt gnd ?in ref load 4v t o 80v 2.5v b a tte r y ad8218 out i charge enb 09592-028 figure 29 . operation wit h no v s connection the ad8218 can also be powered from a separate low impedance supply at pin 2 (v s ); however , this voltage can only be in the 4 v to 5.5 v range. in cases where the high voltage bus is susceptible to noise, transients, or high voltage fluc tuations and a 5 v supply is available , the ad8218 can be used in the mode depicted in figure 30. +in i load v s shunt gnd ?in ref load 4v t o 80v b a tte r y ad8218 out i charge enb 5v 2.5v c f 09592-029 figure 30 . 5 v supply operation enable pin (enb) operation the ad8218 includes an internal reference tha t can be enabled by connecting pin 3 (enb) to ground . this mode of operation is shown in figure 31. +in i load v s shunt gnd ?in ref load 4v t o 80v b a tte r y ad8218 out enb 09592-030 figure 31 . enabling the internal 80 mv reference in this configuration , the internal 80 mv reference i s activated , and the output of the ad8218 is 80 mv when the differential input voltage is 0 v and the voltage at pin 7 ( ref ) is also 0 v. this internal reference is useful in unidirectional current measurements where the current being monitored has a very wide range. setting the output starting point to 80 mv means that when the load current through the shunt resistor is 0 a, the output is 80 m v. this ensures that the output errors due to initial offset and the output saturation range of the amplifier are o vercome. in this mode , the transfer function of the ad8218 becomes ou t (v) = out (v) = (20 v in ) + 0.08 v if pin 3 is connected to ground, and therefore the internal reference is enabled, 80 mv must always be added to the transfer function of the ad8218 .
ad8218 data sheet rev. b | page 12 of 16 a pplications information unidirectional high - side current sensing in the unidirectional high - side current sensing configuration, the shunt resistor is referenced to the battery (see figure 32) . high voltage is present at the inputs of the current sense amplifier. when the shunt is battery referenced , the ad8218 produces a linear ground - referenced analog output. the supply pin, v s , of the ad8218 can eit her be connected to a 5 v supply or left floating ( see the supply (v s ) connections section) . load v 2 i load v 1 shunt battery (4v to 80v) ldo r2 r1 ad8218 r4 r3 +in ?in out enb ref gnd v s 09592-031 figure 32 . unidirectional operation with enb connected to gnd the output transfer function curve for unidirectional operation with enb connected to gnd is shown in figure 33. 0 40 80 120 160 200 240 280 320 0 1 2 3 4 5 6 7 8 9 10 input vo lt age (mv) output vo lt age (mv) 09592-032 figure 33 . output transfer function with enb connected to gnd bidirectional high - side current sensing inputting a voltage at pin 7 (ref) offsets the output of the ad8218 and allows for bidirectional current sensing. the transfer function from the ref pin to the output is 1 v/v . for example, a 2.5 v ref input offset s the output of the ad8218 to 2.5 v . s ee figure 34 for typical connections. the user must ensure that the voltag e applied at pin 7 (ref) is from a low impedance source. shunt ldo r2 r1 ad8218 r4 r3 +in ?in out enb ref 2.5v gnd v s 09592-033 load v 2 i load v 1 battery (4v to 80v) figure 34 . bidirectional operation using a 2.5 v reference input the output transfer function curve for bidirectional operation using a 2.5 v reference input is shown in figure 35. 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 ?0.15 ?0.10 ?0.05 0 0.05 0.10 0.15 input vo lt age (v) output vo lt age (v) 09592-034 figure 35 . transfer function when using a 2.5 v reference input motor control curren t sensing the ad8218 is a practical , accurate solution for high - side current sensing in motor control applications. in cases where the shunt resistor is referenced to a battery and the current flowing is bidirectional ( as shown in figure 36) , the ad8218 monitors the current with no additional supply pin necessary. gnd ba tte r y mo t or i mo t or ad8218 +in v s v ref ?in ref out enb 09592-035 figure 36 . high - side current sensing in motor control
data sheet ad8218 rev. b | page 13 of 16 outline dimension s 081806-a coplanarity 0.08 0.50 0.40 0.30 0.20 min 0.05 max 0.02 nom 0.15 ref 0.50 pin 1 indic a t or exposed p ad bot t om view t o p view 0.30 0.25 0.20 0.80 0.75 0.70 se a ting plane 3.00 bsc side view 1 4 8 5 2.00 bsc index area 1.90 1.80 1.65 1.75 1.65 1.50 for proper connection of the exposed pad, refer to the pin configuration and function descriptions section of this data sheet. figure 37 . 8 - lead lead frame chip scale package [lfcsp_wd] 2 mm 3 mm body, very ve ry thin, dual lead (cp - 8 - 4) dimensions shown in millimeters c o m p l i a n t t o j e d e c s t a n d a r d s m o - 1 8 7 - a a 6 0 0 . 8 0 0 . 5 5 0 . 4 0 4 8 1 5 0 . 6 5 b s c 0 . 4 0 0 . 2 5 1 . 1 0 m a x 3 . 2 0 3 . 0 0 2 . 8 0 c o p l a n a r i t y 0 . 1 0 0 . 2 3 0 . 0 9 3 . 2 0 3 . 0 0 2 . 8 0 5 . 1 5 4 . 9 0 4 . 6 5 p i n 1 i d e n t i f i e r 1 5 m a x 0 . 9 5 0 . 8 5 0 . 7 5 0 . 1 5 0 . 0 5 1 0 - 0 7 - 2 0 0 9 - b figure 38 . 8 - lead mini small outline package [msop] (rm - 8) dimensions shown in millimeters o rdering g uide model 1 temperature range package d e scription package option b randing ad8218bcpz -rl ? 40c to +125c 8- lead lead frame chip scale package [lfcsp_wd] cp -8-4 y5 a ad8218bcpz - wp ? 40c to +125c 8- lead lead frame chip scale package [lfcsp_wd] cp -8-4 y5 a ad8218 b r m z ? 40c to +125c 8- lead mini small outline package [ msop ] rm -8 y3 k ad8218 b r m z -r l ? 40c to +125c 8- lead mini small outline package [ msop ] rm -8 y3 k 1 z = rohs compliant part .
ad8218 data sheet rev. b | page 14 of 16 notes
data sheet ad8218 rev. b | page 15 of 16 notes
ad8218 data sheet rev. b | page 16 of 16 notes ? 2011 C 2013 analog devices, inc. all rights reserved. trademarks and registered trademarks are the property of their respective ow ners. d09592 - 0- 4/13(b)

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