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High Voltage Current Shunt Monitor AD8212
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
FUNCTIONAL BLOCK DIAGRAM
V+ 1 VSENSE 8
AD8212
APPLICATIONS
Current shunt measurement Motor controls DC-to-DC converters Power supplies Battery monitoring Remote sensing
OUTPUT CURRENT COMPENSATION BIAS CIRCUIT 5 IOUT 2 COM 3 BIAS 6 ALPHA
05942-001
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 compensation 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 commonmode voltage or temperature.
Rev. 0
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 (c)2007 Analog Devices, Inc. All rights reserved.
AD8212 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
5/07--Revision 0: Initial Version
Rev. 0 | Page 2 of 16
AD8212 SPECIFICATIONS
VS = 15 V, TOPR = -20C to +125C, TA = 25C, unless otherwise noted. Table 1.
Parameter SUPPLY VOLTAGE (V+) SUPPLY CURRENT 2 Conditions/Comments No external pass transistor With external PNP transistor 1 (ISUPPLY = IOUT + IBIAS) V+ = 7 V to 65 V High voltage operation, using external PNP TA TOPR TOPR Min 7 7 220 200 Typ Max 65 >500 720 1500 2 3 10 Unit V V A A mV mV V/C
VOLTAGE OFFSET Offset Voltage (RTI) Over Temperature (RTI) Offset Drift INPUT Input Impedance Differential Common Mode (VCM) Voltage Range Differential VSENSE (Pin 8) Current 3 OUTPUT Transconductance Current Range (IOUT) Gain Error for TOPR Impedance Voltage Range REGULATOR Nominal Value PSRR Bias Current (IBIAS) DYNAMIC RESPONSE Small Signal -3 dB Bandwidth
V+ = 7 V to 65 V Maximum voltage between V+ and VSENSE V+ = 7 V to 65 V, TOPR
2 5 500 200
k M mV nA
100 1000
7 V V+ 65, 0 to 500 mV differential input 7 V V+ 65, with respect to 500 A full scale 20 0 7 V V+ 65 V 7 V V+ 65 V TOPR, 7 V V+ 65 V TOPR, high voltage operation Gain = 10 Gain = 20 Gain = 50 Within 0.1% of the true output, gain = 20 4.80 80 200 1000 500 100 2 5 185
A/V A % M V+ - 5 V 500 1 5.20 200 1000 V dB A A kHz kHz kHz s A V p-p nV/Hz +125 C
Settling Time ALPHA PIN INPUT CURRENT NOISE 0.1 Hz to 10 Hz, RTI Spectral Density, 1 kHz RTI TEMPERATURE RANGE For Specified Performance (TOPR)
1 2
25 1.1 40 -20
Range dependent on the VCE breakdown of the transistor. The AD8212 supply current in normal voltage operation (V+ = 7 V to 65 V) is the bias current (IBIAS) added to output current (IOUT). Output current varies upon input differential voltage and can range from 0 A to 500 A. IBIAS in this mode of operation is typically 185 A and maximum 200 A. For high voltage operation mode, refer to the High Voltage Operation Using an External PNP Transistor section. 3 The current into VSENSE (Pin 8) of the amplifier increases when operating in high voltage mode. See the High Voltage Operation Using an External PNP Transistor section for more information.
Rev. 0 | Page 3 of 16
AD8212 ABSOLUTE MAXIMUM RATINGS
TOPR = -20C to +125C, unless otherwise noted. Table 2.
Parameter Supply Voltage Continuous Input Voltage Reverse Supply Voltage Operating Temperature Range Storage Temperature Range Output Short-Circuit Duration Rating 65 V 68 V 0.3 V -20C to +125C -40C to +150C Indefinite
ESD CAUTION
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.
Rev. 0 | Page 4 of 16
AD8212 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
V+ 1 COM 2 BIAS 3
8
AD8212
VSENSE NC
05942-002
7
1 2 3
8 7 6
05942-025
6 ALPHA TOP VIEW NC 4 (Not to Scale) 5 IOUT
5
NC = NO CONNECT
Figure 2. Pin Configuration
Figure 3. Metallization Diagram
Table 3. Pin Function Descriptions
Pin No. 1 2 3 4 5 6 7 8 Mnemonic V+ COM BIAS NC IOUT ALPHA NC VSENSE X Coordinate -393 -392 -392 - 386 386 386 386 Y Coordinate 219 67 -145 - -82 23 118 210 Description Supply Voltage (Inverting Amplifier Input). Regulator Low Side. Bias Circuit Low Side No Connect. Output Current. Current Compensation Circuit Input. No Connect. Noninverting Amplifier Input.
Rev. 0 | Page 5 of 16
AD8212 TYPICAL PERFORMANCE CHARACTERISTICS
195 190
1200
T = +125C
1000
QUIESCENT CURRENT (A)
185 180 175 170 165 160
200
05942-005
05942-008
T = +25C
T = -40C
INPUT VOS (V)
55 60 65
800
600
400
5
10
15
20
25
30
35
40
45
50
0 -40
-20
0
20
40
60
80
100
120
SUPPLY VOLTAGE (V)
TEMPERATURE (C)
Figure 4. Supply Current vs. Supply (Pin V+) (IOUT = 0 mA)
5.2
Figure 7. Input Offset Voltage vs. Temperature
1.0 0.9 +125C
REGULATOR VOLTAGE (V)
5.1 T = -40C
OFFSET VOLTAGE RTI (mV)
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 7 12 17 22 27 32 37 42 47 52 57 62
05942-009
T = +25C 5.0
+25C
4.9 T = +125C
05942-006
-40C
4.8
5
10
15
20
25
30
35
40
45
50
55
60
65
SUPPLY VOLTAGE (V)
VOLTAGE SUPPLY (V)
Figure 5. Regulator Voltage vs. Supply (Pin V+)
Figure 8 .Input Offset Voltage vs. Supply (Pin V+)
50 45 40 35 G = +50
10 9
OUTPUT CURRENT DRIFT (nA/C)
8 7 6 5 4 3 2 1
05942-010
GAIN (dB)
30 G = +20 25 20 15 10 5 10k 100k FREQUENCY (Hz) 1M 10M
05942-021
G = +10
0 1k
0
0
50
100
150
200
250
300
350
400
450
500
DIFFERENTIAL INPUT VOLTAGE (mV)
Figure 6. Gain vs. Frequency
Figure 9. Output Current Drift vs. Differential Input Voltage
Rev. 0 | Page 6 of 16
AD8212
100
VIN 20mV/DIV
10
OUTPUT ERROR (%)
1
V+ = 15V ROUT = 50k
G = +10 G = +20
VOUT 500mV/DIV 0V
0.1
G = +50
05942-014
0
10
20
30
40
50
60
70
80
90
100
500
DIFFERENTIAL INPUT VOLTAGE (mV)
Figure 10. Total Output Error Due to Input Offset vs. Differential Input Voltage
05942-023
0.01
5s/DIV
Figure 13. Step Response (Gain = 50)
VIN 20mV/DIV
VIN 100mV/DIV
V+ = 15V ROUT = 5k VOUT 50mV/DIV 0V VOUT 200mV/DIV
V+ = 15V ROUT = 5k
05942-012
5s/DIV
5s/DIV
Figure 11. Step Response (Gain = 5)
Figure 14. Step Response (Gain = 5)
VIN 20mV/DIV
VIN 100mV/DIV
V+ = 15V ROUT = 20k VOUT 200mV/DIV 0V
0V VOUT 1V/DIV
V+ = 15V ROUT = 20k
05942-013
5s/DIV
5s/DIV
Figure 12. Step Response (Gain = 20)
Figure 15. Step Response (Gain = 20)
Rev. 0 | Page 7 of 16
05942-016
05942-015
AD8212
5.2
VIN 100mV/DIV
REGULATOR VOLTAGE (V)
5.1 T = -40C T = +25C 5.0 T = +125C
V+ = 15V ROUT = 50k VOUT 2V/DIV 0V
4.9
05942-017
BIAS CURRENT (A)
Figure 16. Step Response (Gain = 50)
Figure 19. Regulator Voltage High Voltage Mode (IOUT = 0 mA) vs. Supply Current
5.2
VIN 100mV/DIV
REGULATOR VOLTAGE (V)
5.1 V+ = 300V V+ = 100V
V+ = 15V ROUT = 20k VOUT 2V/DIV 0V
05942-018
5.0 V+ = 200V 4.9
2s/DIV
4.8 -40
-25
-10
5
20
35
50
65
80
95
110 125
TEMPERATURE (C)
Figure 17. Step Response Falling
550
Figure 20. Regulator Voltage vs. Temperature (High Voltage Operation)
VIN 100mV/DIV
V+ OPERATING RANGE (V)
500 450 400 350 300 250 200 150 100 50 20 30 50 70 100 150 200 250 300 350 400 450 500 RBIAS (k)
05942-020
V+ = 15V ROUT = 20k
0V
VOUT 2V/DIV
05942-019
V+ MAXIMUM RANGE V+ MINIMUM RANGE
2s/DIV
0 10
Figure 18. Step Response Rising
Figure 21. Supply Range (V+) vs. Bias Resistor Value (High Voltage Operation)
Rev. 0 | Page 8 of 16
05942-007
05942-024
5s/DIV
4.8 100
200
300
400
500
600
700
800
900 1000 1100 1200
AD8212 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 (RSHUNT) 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 (IOUT) is proportional to the input voltage (VSENSE), and, therefore, the load current (ILOAD) through the shunt resistor (RSHUNT). The output current (IOUT) 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 IOUT = (gm x VSENSE) VSENSE = ILOAD x RSHUNT VOUT = IOUT x ROUT VOUT = (VSENSE x ROUT)/1000 where: gm = 1000 A/V. In normal voltage operation mode, the bias circuit is connected to GND, as shown in Figure 22. In this mode, IBIAS is typically 185 A throughout the 7 V to 65 V (V+) range. Table 4. Suggested ROUT Values
Gain (V/V) 1 10 20 50 100 ROUT (k) 1 10 20 49.9 100
VOUT ROUT BATTERY 1 R1 RSHUNT ILOAD 8
AD8212
R2
LOAD
A1
Q1
BIAS CIRCUIT 5 IOUT 2 3
OUTPUT CURRENT COMPENSATION
6
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 ROUT values.
Rev. 0 | Page 9 of 16
05942-003
AD8212
HIGH VOLTAGE OPERATION USING AN EXTERNAL PNP TRANSISTOR
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 VCE breakdown voltage of this PNP becomes the operating common-mode range of the AD8212. PNP transistors with breakdown voltages exceeding 300 V, are readily available, inexpensive, and available in small packages.
BATTERY 1 R1 RSHUNT 8
In this mode of operation, the supply current (IBIAS) of the AD8212 circuit increases based on the supply range and the RBIAS resistor chosen. For example: if V+ = 500 V and RBIAS = 500 k IBIAS = (V+ - 5 V)/RBIAS then, IBIAS = (500 - 5)/500 k = 990 A In high voltage operation, it is recommended that IBIAS 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 IBIAS and V+ information when using the AD8212 in a high voltage configuration. 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 IOUT conducted to the output resistor (ROUT) is reduced by the amount of current lost through the base of the PNP. This leads to an error in the output voltage reading.
AD8212
R2
LOAD
A1
Q1
BIAS CIRCUIT 5 Q2 VOUT 2 3
OUTPUT CURRENT COMPENSATION
6
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.
05942-004
ROUT
RBIAS
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 IOUT. Since 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 IOUT such that no error results from the base current lost at Transistor Q2. This feature of the AD8212 greatly improves IOUT 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).
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+) - 5 V = 95 V The base emitter junction of Transistor Q2, in addition to the Vbe of one internal transistor, makes the collector of Transistor Q1 approximately equal to 95 V + 2(Vbe(Q2)) = 95 V + 1.2 V = 96.2 V This voltage appears across external Transistor Q2. The voltage across Transistor Q1 is 100 V - 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.
Rev. 0 | Page 10 of 16
AD8212 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 ROUT be buffered, so that the gain of the AD8212 is not affected.
ILOAD BATTERY RSHUNT
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.
ILOAD 500V RSHUNT LOAD VOUT ROUT
AD8212
1 2 3 4
V+ COM NC
VSENSE NC IOUT
8 7 6 5
BIAS ALPHA
LOAD
ADC
AD8661
05942-026
IOUT
ROUT
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 ROUT, which can be as high as 500 A (based on a 500 mV maximum input differential limit).
AD8212
1 2 3 4
V+ COM NC
VSENSE 8 NC 7 IOUT 5
BIAS ALPHA 6
500k
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.
BATTERY
Figure 26. High Voltage Operation Using External PNP
AD8212
1 2 3 4
IMOTOR
8 7 6 5
V+ COM NC
VSENSE NC IOUT
BIAS ALPHA
MOTOR VOUT ROUT
NOTES 1. NC = NO CONNECT.
Figure 25. High-Side Current Sensing for Motor Control
05942-028
Rev. 0 | Page 11 of 16
05942-027
NOTES 1. TRANSISTOR VCE BREAKDOWN VOLTAGE MUST BE 500V. 2. NC = NO CONNECT.
AD8212
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,
ILOAD ICHARGE RSHUNT
VOUT1 increases as ILOAD flows through the shunt resistor. VOUT2 increases when ICHARGE flows through the input shunt resistor.
BATTERY
CHARGE
ROUT2
V+ 1
VSENSE
8
8
VSENSE
V+ 1
AD8212
AD8212
OUTPUT CURRENT COMPENSATION BIAS CIRCUIT IOUT 5 2 COM 3 BIAS 6 VOUT1 ROUT1 ALPHA
OUTPUT CURRENT COMPENSATION BIAS CIRCUIT ALPHA 6 BIAS 3 COM 2 IOUT 5 VOUT2
05942-011
Figure 27. Bidirectional Current Sensing
Rev. 0 | Page 12 of 16
LOAD
AD8212 OUTLINE DIMENSIONS
3.20 3.00 2.80
8 5
3.20 3.00 2.80 PIN 1
1
5.15 4.90 4.65
4
0.65 BSC 0.95 0.85 0.75 0.15 0.00 0.38 0.22 SEATING PLANE 1.10 MAX 8 0 0.80 0.60 0.40
0.23 0.08
COPLANARITY 0.10
COMPLIANT TO JEDEC STANDARDS MO-187-AA
Figure 28. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters
ORDERING GUIDE
Model AD8212YRMZ 1 AD8212YRMZ-RL1 AD8212YRMZ-R71
1
Temperature Range -20C to +125C -20C to +125C -20C to +125C
Package Description 8-Lead MSOP 8-Lead MSOP, 13" Tape and Reel 8-Lead MSOP, 7" Tape and Reel
Package Option RM-8 RM-8 RM-8
Branding Y04 Y04 Y04
Z = RoHS Compliant Part.
Rev. 0 | Page 13 of 16
AD8212 NOTES
Rev. 0 | Page 14 of 16
AD8212 NOTES
Rev. 0 | Page 15 of 16
AD8212 NOTES
(c)2007 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D05942-0-5/07(0)
Rev. 0 | Page 16 of 16

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