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high voltage current shunt monitor ad8212 rev. b 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 result 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 www.analog.com fax: 781.461.3113 ?2007C2009 analog devices, inc. all rights reserved. features adjustable gain high common-mode voltage range 7 v to 65 v typical 7 v to >500 v with external pass transistor current output integrated 5 v series regulator 8-lead msop package operating temperature range of ?40c to +125c applications current shunt measurement motor controls dc-to-dc converters power supplies battery monitoring remote sensing functional block diagram ad8212 v+ i out com bias alpha v sense 05942-001 output current compensation bias circuit 8 6 3 2 5 1 figure 1. general description the ad8212 is a high common-mode voltage, current shunt monitor. it accurately amplifies a small differential input voltage in the presence of large common-mode voltages up to 65 v (>500 v with an external pnp transistor). the ad8212 is ideal for current monitoring across a shunt resistor in applications controlling loads, such as motors and solenoids. the current output of the device is proportional to the input differential voltage. the user can select an external resistor to set the desired gain. the typical common-mode voltage range of the ad8212 is 7 v to 65 v. another feature of the ad8212 is high voltage operation, which is achieved by using an external high voltage breakdown pnp transistor. in this configuration, the common-mode range of the ad8212 is equal to the breakdown of the external pnp transistor. therefore, operation at several hundred volts is easily achieved (see figure 23 ). the ad8212 features a patented output base current compensa- tion circuit for high voltage operation mode. this ensures that no base current is lost through the external transistor and excellent output accuracy is maintained regardless of common- mode voltage or temperature.
ad8212 rev. b | page 2 of 16 table of contents features .............................................................................................. 1 applications ....................................................................................... 1 functional block diagram .............................................................. 1 general description ......................................................................... 1 revision history ............................................................................... 2 specifications ..................................................................................... 3 absolute maximum ratings ............................................................ 4 esd caution .................................................................................. 4 pin configuration and function descriptions ............................. 5 typical performance characteristics ............................................. 6 theory of operation ........................................................................ 9 normal operation (7 v to 65 v supply (v+) range) ..............9 high voltage operation using an external pnp transistor 10 output current compensation circuit ................................... 10 applications information .............................................................. 11 general high-side current sensing ........................................ 11 motor control ............................................................................. 11 500 v current monitor ............................................................. 11 bidirectional current sensing .................................................. 12 outline dimensions ....................................................................... 13 ordering guide .......................................................................... 13 revision history 5/09rev. a to rev. b changes to ordering guide .......................................................... 13 11/07rev. 0 to rev. a increased operating temperature range ........................ universal 5/07revision 0: initial version
ad8212 rev. b | page 3 of 16 specifications v s = 15 v, t opr = ?40c to +125c, t a = 25c, unless otherwise noted. table 1. parameter conditions/comments min typ max unit supply voltage (v+) no external pass transistor 7 65 v with external pnp transistor 1 7 >500 v supply current 2 (i supply = i out + i bias ) v+ = 7 v to 65 v 220 720 a high voltage operation, using external pnp 200 1500 a voltage offset offset voltage (rti) t a 2 mv over temperature (rti) t opr 3 mv offset drift t opr 10 v/c input input impedance differential 2 k common mode (v cm ) v+ = 7 v to 65 v 5 m voltage range differential maximum voltage between v+ and v sense 500 mv v sense (pin 8) current 3 v+ = 7 v to 65 v, t opr 100 200 na output transconductance 1000 a/v current range (i out ) 7 v v+ 65 v, 0 mv to 500 mv differential input 500 a gain error for t opr 7 v v+ 65 v, with respect to 500 a full scale 1 % impedance 20 m voltage range 0 v+ ? 5 v regulator nominal value 7 v v+ 65 v 4.80 5 5.20 v psrr 7 v v+ 65 v 80 db bias current (i bias ) t opr , 7 v v+ 65 v 185 200 a t opr , high voltage operation 200 1000 a dynamic response small signal ?3 db bandwidth gain = 10 1000 khz gain = 20 500 khz gain = 50 100 khz settling time within 0.1% of the true output, gain = 20 2 s alpha pin input current 25 a noise 0.1 hz to 10 hz, rti 1.1 v p-p spectral density, 1 khz, rti 40 nv/ hz temperature range for specified performance (t opr ) ?40 +125 c 1 range dependent on the v ce breakdown of the transistor. 2 the ad8212 supply current in normal voltage operat ion (v+ = 7 v to 65 v) is the bias current (i bias ) added to output current (i out ). output current varies upon input differential voltag e and can range from 0 a to 500 a. i bias in this mode of operation is typi cally 185 a and 200 a maximum. for high voltage operation mode, refer to the hi section. gh voltage operation using an external pnp transistor high voltage operation using an external pnp transistor 3 the current of the amplifier into v sense (pin 8) increases when operating in high voltage mode. see the section for more information.
ad8212 rev. b | page 4 of 16 absolute maximum ratings t opr = ?40 c to +125 c, unless otherwise noted. table 2. parameter rating supply voltage 65 v continuous input voltage 68 v reverse supply voltage 0.3 v operating temperature range ?40c to +125c storage temperature range ?40c 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
ad8212 rev. b | page 5 of 16 pin configuration and fu nction descriptions 05942-002 v+ 1 com 2 bias 3 nc 4 v sense 8 nc 7 alpha 6 i out 5 nc = no connect ad8212 top view (not to scale) figure 2. pin configuration 1 2 3 8 6 5 05942-025 figure 3. metallization diagram table 3. pin function descriptions pin no. mnemonic x coordinate y coordinate description 1 v+ ?393 +219 supply voltage (inverting amplifier input). 2 com ?392 +67 regulator low side. 3 bias ?392 ?145 bias circuit low side. 4 nc C C no connect. 5 i out +386 ?82 output current. 6 alpha +386 +23 current compensation circuit input. 7 nc +386 +118 no connect. 8 v sense +386 +210 noninverting amplifier input.
ad8212 rev. b | page 6 of 16 typical performance characteristics 195 175 180 185 190 170 165 160 5 101520253035404550556065 quiescent current (a) supply voltage (v) 05942-005 t = +125c t = +25c t = ?40c figure 4. supply current vs. supply (pin v+) (i out = 0 ma) 5.2 5.0 5.1 4.9 4.8 5 101520253035404550556065 regulator voltage (v) supply voltage (v) 05942-006 t = ?40c t = +25c t = +125c figure 5. regulator voltage vs. supply (pin v+) 0 5 10 15 20 25 30 35 40 45 50 1k 10k 100k 1m 10m g = +50 g = +20 g = +10 0 5942-021 frequency (hz) gain (db) figure 6. gain vs. frequency 1200 1000 400 600 800 200 0 ?40 ?20 0 20 40 60 80 100 120 input v os ( v ) temperature (c) 05942-008 figure 7. input offset voltage vs. temperature 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.1 0 7 1217222732374247525762 voltage supply (v) 05942-009 +125c +25c ?40c offset voltage rti (mv) figure 8 .input offset voltage vs. supply (pin v+) 2 3 4 5 6 7 8 9 10 1 0 0 50 100 150 200 250 300 350 400 450 500 output current drift (na/c) differential input voltage (mv) 05942-010 figure 9. output current drift vs. differential input voltage
ad8212 rev. b | page 7 of 16 0.01 0.1 1 10 100 0 10203040 60 80 100 50 70 90 500 05942-023 differential input voltage (mv) output error (%) g = +20 g = +10 g = +50 figure 10. total output error due to input offset vs. differential input voltage 05942-012 5s/div 0v v out 50mv/div v+ = 15v r out = 5k ? v in 20mv/div figure 11. step response (gain = 5) 05942-013 5s/div 0v v out 200mv/div v+ = 15v r out = 20k ? v in 20mv/div figure 12. step response (gain = 20) 05942-014 5s/div 0v v out 500mv/div v+ = 15v r out = 50k ? v in 20mv/div figure 13. step response (gain = 50) 05942-015 5s/div v out 200mv/div v+ = 15v r out = 5k ? v in 100mv/div figure 14. step response (gain = 5) 05942-016 5s/div 0v v out 1v/div v+ = 15v r out = 20k ? v in 100mv/div figure 15. step response (gain = 20)
ad8212 rev. b | page 8 of 16 05942-017 5s/div 0v v out 2v/div v+ = 15v r out = 50k ? v in 100mv/div figure 16. step response (gain = 50) 05942-018 2s/div 0v v out 2v/div v+ = 15v r out = 20k ? v in 100mv/div figure 17. step response falling 05942-019 2s/div 0v v out 2v/div v+ = 15v r out = 20k ? v in 100mv/div figure 18. step response rising 0 5942-024 bias current (a) regulator voltage (v) 4.8 4.9 5.0 5.1 5.2 100 200 300 400 500 600 700 800 900 1000 1100 1200 t = ?40c t = +125c t = +25c figure 19. regulator voltage high voltage mode (i out = 0 ma) vs. bias current 5.2 5.0 5.1 4.9 4.8 ?40 ?25 ?10 5 20 35 50 65 80 95 110 125 regulator voltage (v) temperature (c) 05942-007 v+ = 300v v+ = 100v v+ = 200v figure 20. regulator voltage vs. temperature (high voltage operation) 05942-020 r bias (k ? ) v+ operating range (v) 550 500 450 400 350 300 250 200 150 100 50 0 10 20 30 50 70 100 150 200 250 300 350 400 450 500 v+ maximum range v+ minimum range figure 21. supply range (v+) vs. bias resistor value (high voltage operation)
ad8212 rev. b | page 9 of 16 theory of operation normal operation (7 v to 65 v supply (v+) range) in typical applications, the ad8212 measures a small differential input voltage generated by a load current flowing through a shunt resistor. the operational amplifier (a1) is connected across the shunt resistor (r shunt ) with its inverting input connected to the battery/supply side, and the noninverting input connected to the load side of the system. amplifier a1 is powered via an internal series regulator (depicted as a zener diode in figure 22 ). this regulator maintains a constant 5 v between the battery/supply terminal of the ad8212 and com (pin 2), which represents the lowest common point of the internal circuitry. a load current flowing through the external shunt resistor produces a voltage at the input terminals of the ad8212. amplifier a1 responds by causing transistor q1 to conduct the necessary current through resistor r1 to equalize the potential at both the inverting and noninverting inputs of amplifier a1. the current through the emitter of transistor q1 (i out ) is proportional to the input voltage (v sense ), and, therefore, the load current (i load ) through the shunt resistor (r shunt ). the output current (i out ) is converted to a voltage by using an external resistor, the value of which is dependent on the input to output gain equation desired in the application. the transfer function for the ad8212 is i out = ( g m v sense ) v sense = i load r shunt v out = i out r out v out = (v sense r out )/ 1000 where: g m = 1000 a/v. in normal voltage operation mode, the bias circuit is connected to gnd, as shown in figure 22 . in this mode, i bias is typically 185 a throughout the 7 v to 65 v (v+) range. i out i load r out ad8212 battery r shunt 05942-003 output current compensation load r1 r2 a1 q1 v out bias circuit 8 6 3 2 5 1 figure 22. typical connection (7 v to 65 v supply (pin v+) range) when using the ad8212 as described, the battery/supply voltage in the system must be between 7 v to 65 v. the 7 v minimum supply range is necessary to turn on the internal regulator (shown as a zener diode in figure 22 ). this regulated voltage then remains a constant 5 v, regardless of the supply (v+) voltage. the 65 v maximum limit in this mode of operation is due to the breakdown voltage limitation of the ad8212 process. typically, a 1% resistor can be used to convert the output current to a voltage. table 4 provides suggested r out values. table 4. suggested r out values gain (v/v) r out (k) 1 1 10 10 20 20 50 49.9 100 100
ad8212 rev. b | page 10 of 16 high voltage operation using an external pnp transistor in this mode of operation, the supply current (i bias ) of the ad8212 circuit increases based on the supply range and the r bias resistor chosen. for example the ad8212 offers features that simplify measuring current in the presence of common-mode voltages greater than 65 v. this is achieved by connecting an external pnp transistor at the output of the ad8212, as shown in figure 23 . the v ce break- down voltage of this pnp becomes the operating common-mode range of the ad8212. pnp transistors with breakdown voltages exceeding 300 v are inexpensive and readily available in small packages. if v+ = 500 v and r bias = 500 k i bias = (v+ ? 5 v)/ r bias then, i bias = (500 C 5)/500 k = 990 a in high voltage operation, it is recommended that i bias remain within 200 a to 1 ma. this ensures that the bias circuit is turned on, allowing the device to function as expected. at the same time, the current through the bias circuit/regulator is limited to 1 ma. refer to figure 19 and figure 21 for i bias and v+ information when using the ad8212 in a high voltage configuration. r out q2 ad8212 b a tte r y r shunt 05942-004 output current compensation bias circuit load r1 r2 a1 q1 vout r bias 8 6 3 2 5 1 when operating the ad8212, as depicted in figure 23 , transistor q2 can be a fet or a bipolar pnp transistor. the latter is much less expensive, however the magnitude of i out conducted to the output resistor (r out ) is reduced by the amount of current lost through the base of the pnp. this leads to an error in the output voltage reading. the ad8212 includes an integrated patented circuit, which compensates for the output current that is lost through the base of the external pnp transistor. this ensures that the correct transconductance of the amplifier is maintained. the user can opt for an inexpensive bipolar pnp, instead of a fet, while maintaining a comparable level of accuracy. output current compensation circuit the base of the external pnp, q2, is connected to alpha (pin 6) of the ad8212. the current flowing in this path is mirrored inside the current compensation circuit. this current then flows in resistor r2, which is the same value as resistor r1. the voltage created by this current across resistor r2, displaces the noninverting input of amplifier a1 by the corresponding voltage. amplifier a1 responds by driving the base of transistor q1 so as to force a similar voltage displacement across resistor r1, thereby increasing i out . figure 23. high voltage operation using external pnp the ad8212 features an integrated 5 v series regulator. this regulator ensures that at all times com (pin 2), which is the most negative of all the terminals, is always 5 v less than the supply voltage (v+). assuming a battery voltage (v+) of 100 v, it follows that the voltage at com (pin 2) is ( v +) C 5 v = 95 v the base emitter junction of transistor q2, in addition to the v be of one internal transistor, makes the collector of transistor q1 approximately equal to because the current generated by the output compensation circuit is equal to the base current of transistor q2, and the resulting displacements across resistor r1 and resistor r2 result in equal currents, the increment of current added to the output current is equivalent to the base current of transistor q2. therefore, the integrated output current compensation circuit has corrected i out such that no error results from the base current lost at transistor q2. 95 v + 2( v be(q2) ) = 95 v + 1.2 v = 96.2 v this voltage appears across external transistor q2. the voltage across transistor q1 is 100 v C 96.2 v = 3.8 v in this manner, transistor q2 withstands 95.6 v and the internal transistor q1 is only subjected to voltages well below its breakdown capability. this feature of the ad8212 greatly improves i out accuracy and allows the user to choose an inexpensive bipolar pnp (with low beta) with which to monitor current in the presence of high voltages (typically several hundred volts).
ad8212 rev. b | page 11 of 16 applications information general high-side current sensing the ad8212 output is intended to drive high impedance nodes. therefore, if interfacing with a converter, it is recommended that the output voltage across r out be buffered, so that the gain of the ad8212 is not affected. ad8661 05942-026 v+ 1 com 2 bias 3 nc 4 v sense 8 nc 7 alpha 6 i out 5 ad8212 i load i out battery r shunt load adc r out notes 1. nc = no connect. figure 24. normal voltage range operation careful calculations must be made when choosing a gain resistor so as not to exceed the input voltage range of the converter. the output of the ad8212 can be as high as (v+) ? 5 v. however, the true output maximum voltage is dependent upon the differential input voltage, and the resulting output current across r out , which can be as high as 500 a (based on a 500 mv maximum input differential limit). motor control the ad8212 is a practical solution for high-side current sensing in motor control applications. in cases where the shunt resistor is referenced to battery and the current flowing is unidirectional, as shown in figure 25 , the ad8212 monitors the current with no additional supply pin necessary. 05942-028 r out motor v+ 1 com 2 bias 3 nc 4 v sense 8 nc 7 alpha 6 i out 5 ad8212 i motor v out b a tte r y notes 1. nc = no connect. figure 25. high-side current sensing for motor control 500 v current monitor as noted in the high voltage operation using an external pnp transistor section, the ad8212 common-mode voltage range is extended by using an external pnp transistor. this mode of operation is achievable with many amplifiers featuring a current output. however, typically an external zener regulator must be added, along with a fet device, to withstand the common-mode voltage and maintain output current accuracy. the ad8212 features an integrated regulator (which acts as a zener regulator). it offers output current compensation that allows the user to maintain excellent output current accuracy by using any pnp transistor. reliability is increased due to lower component count. most importantly, the output current accuracy is high, allowing the user to choose an inexpensive pnp transistor to withstand the increased common-mode voltage. 05942-027 v+ 1 com 2 bias 3 nc 4 v sense 8 nc 7 alpha 6 i out 5 ad8212 i load 500v r shunt load r out 500k ? vout notes 1. transistor v ce breakdown voltage must be 500v. 2. nc = no connect. figure 26. high voltage operation using external pnp
ad8212 rev. b | page 12 of 16 bidirectional current sensing the ad8212 is a unidirectional current sensing device. therefore, in power management applications where both the charge and load currents must be monitored, two devices can be used and connected as shown in figure 27 . in this case, v out 1 increases as i load flows through the shunt resistor. v out 2 increases when i charge flows through the input shunt resistor. v out 1 i load r out 1 i out com bias alpha i out v sense v sense v+ v+ com bias alpha ad8212 r shunt output current compensation load i charge v out 2 r out 2 ad8212 output current compensation 0 5942-011 charge battery bias circuit bias circuit 8 8 6 3 2 5 6 3 2 5 1 1 figure 27. bidirectional current sensing
ad8212 rev. b | page 13 of 16 outline dimensions compliant to jedec standards mo-187-aa 0.80 0.60 0.40 8 0 4 8 1 5 pin 1 0.65 bsc seating plane 0.38 0.22 1.10 max 3.20 3.00 2.80 coplanarity 0.10 0.23 0.08 3.20 3.00 2.80 5.15 4.90 4.65 0.15 0.00 0.95 0.85 0.75 figure 28. 8-lead mini small outline package [msop] (rm-8) dimensions shown in millimeters ordering guide model temperature range package desc ription package option branding ad8212yrmz 1 ?40c to +125c 8-lead msop rm-8 y04 ad8212yrmz-rl 1 ?40c to +125c 8-lead msop, 13 tape and reel rm-8 y04 ad8212yrmz-r7 1 ?40c to +125c 8-lead msop, 7 tape and reel rm-8 y04 ad8212wyrmz 1 ?40c to +125c 8-lead msop rm-8 y25 ad8212wyrmz-rl 1 ?40c to +125c 8-lead msop, 13 tape and reel rm-8 y25 ad8212wyrmz-r7 1 ?40c to +125c 8-lead msop, 7 tape and reel rm-8 y25 1 z = rohs compliant part.
ad8212 rev. b | page 14 of 16 notes
ad8212 rev. b | page 15 of 16 notes
ad8212 rev. b | page 16 of 16 notes ?2007C2009 analog devices, inc. all rights reserved. trademarks and registered trademarks are the prop erty of their respective owners. d05942-0-5/09(b)

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