High Voltage
Current Shunt Monitor
AD8212
Rev. B
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responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
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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 −40°C to +125°C
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
6325
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
5/09—Rev. A to Rev. B
Changes to Ordering Guide .......................................................... 13
11/07—Rev. 0 to Rev. A
Increased Operating Temperature Range ........................ Universal
5/07—Revision 0: Initial Version
AD8212
Rev. B | Page 3 of 16
SPECIFICATIONS
VS = 15 V, TOPR = −40°C to +125°C, TA = 25°C, 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 transistor1
7 >500 V
SUPPLY CURRENT2 (ISUPPLY = IOUT + IBIAS)
V+ = 7 V to 65 V 220 720 μA
High voltage operation, using external PNP 200 1500 μA
VOLTAGE OFFSET
Offset Voltage (RTI) TA ±2 mV
Over Temperature (RTI) TOPR ±3 mV
Offset Drift TOPR ±10 μV/°C
INPUT
Input Impedance
Differential 2
Common Mode (VCM) V+ = 7 V to 65 V 5
Voltage Range
Differential Maximum voltage between V+ and VSENSE 500 mV
VSENSE (Pin 8) Current3
V+ = 7 V to 65 V, TOPR 100 200 nA
OUTPUT
Transconductance 1000 μA/V
Current Range (IOUT) 7 V ≤ V+ ≤ 65 V, 0 mV to 500 mV differential input 500 μA
Gain Error for TOPR 7 V ≤ V+ ≤ 65 V, with respect to 500 μA full scale ±1 %
Impedance 20
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 (IBIAS) TOPR, 7 V ≤ V+ ≤ 65 V 185 200 μA
TOPR, high voltage operation 200 1000 μA
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 μs
ALPHA PIN INPUT CURRENT 25 μA
NOISE
0.1 Hz to 10 Hz, RTI 1.1 μV p-p
Spectral Density, 1 kHz, RTI 40 nV/Hz
TEMPERATURE RANGE
For Specified Performance (TOPR) −40 +125 °C
1 Range dependent on the VCE breakdown of the transistor.
2 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 μA to 500 μA. IBIAS in this mode of operation is typically 185 μA and 200 μA 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 VSENSE (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
TOPR = −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 −40°C to +125°C
Storage Temperature Range −40°C to +150°C
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 FUNCTION DESCRIPTIONS
05942-002
V+ 1
COM 2
BIAS 3
NC 4
VSENSE
8
NC
7
ALPHA
6
IOUT
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 No Connect.
5 IOUT +386 −82 Output Current.
6 ALPHA +386 +23 Current Compensation Circuit Input.
7 NC +386 +118 No Connect.
8 VSENSE +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 CURRENTA)
SUPPLY VOLTAGE (V)
05942-005
T = +125°C
T = +25°C T = –40°C
Figure 4. Supply Current vs. Supply (Pin V+) (IOUT = 0 mA)
5.2
5.0
5.1
4.9
4.8
5 101520253035404550556065
REGULATOR VOLTAGE (V)
SUPPLY VOLTAGE (V)
05942-006
T = –40°C
T = +25°C
T = +125°C
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
(
µ
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
+125°C
+25°C
–40°C
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 10050 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
5µs/DIV
0V
VOUT
50mV/DIV
V+ = 15V
ROUT = 5k
VIN
20mV/DIV
Figure 11. Step Response (Gain = 5)
05942-013
5µs/DIV
0V
V
OUT
200mV/DIV
V+ = 15V
R
OUT
= 20k
V
IN
20mV/DIV
Figure 12. Step Response (Gain = 20)
05942-014
5µs/DIV
0V
V
OUT
500mV/DIV
V+ = 15V
R
OUT
= 50k
V
IN
20mV/DIV
Figure 13. Step Response (Gain = 50)
05942-015
5µs/DIV
VOUT
200mV/DIV
V+ = 15V
ROUT = 5k
VIN
100mV/DIV
Figure 14. Step Response (Gain = 5)
05942-016
5µs/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
5µs/DIV
0V
V
OUT
2V/DIV
V+ = 15V
R
OUT
= 50k
V
IN
100mV/DIV
Figure 16. Step Response (Gain = 50)
05942-018
2µs/DIV
0V
V
OUT
2V/DIV
V+ = 15V
R
OUT
= 20k
V
IN
100mV/DIV
Figure 17. Step Response Falling
05942-019
2µs/DIV
0V
VOUT
2V/DIV
V+ = 15V
ROUT = 20k
VIN
100mV/DIV
Figure 18. Step Response Rising
0
5942-024
BIAS CURRENTA)
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 = –40°C
T = +125°C
T = +25°C
Figure 19. Regulator Voltage High Voltage Mode (IOUT = 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
010 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 (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 × VSENSE)
VSENSE = ILOAD × RSHUNT
VOUT = IOUT × ROUT
VOUT = (VSENSE × ROUT)/1000
where:
gm = 1000 µA/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 μA 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
6325
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. Ta ble 4 provides suggested ROUT values.
Table 4. Suggested ROUT Values
Gain (V/V) ROUT (kΩ)
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 (IBIAS) of the
AD8212 circuit increases based on the supply range and the
RBIAS 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 VCE 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 RBIAS = 500 kΩ
IBIAS = (V+ − 5 V)/RBIAS
then,
IBIAS = (500 – 5)/500 kΩ = 990 μA
In high voltage operation, it is recommended that IBIAS remain
within 200 μA 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.
R
OUT
Q2
AD8212
B
A
TTE
R
YR
SHUNT
05942-004
OUTPUT
CURRENT
COMPENSATION
BIAS
CIRCUIT
LOAD
R1 R2
A1
Q1
VOUT
R
BIAS
8
6325
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 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.
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 IOUT.
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
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 IOUT such that no error results from the base
current lost at Transistor Q2.
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.
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).
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 ROUT 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 ROUT, which can be as high as 500 μA
(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
COM2
BIAS
3
NC
4
VSENSE 8
NC 7
ALPHA 6
IOUT 5
AD8212
ILOAD
500V RSHUNT
LOAD
ROUT
500k
VOUT
NOTES
1. TRANSISTOR VCE 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,
VOUT1 increases as ILOAD flows through the shunt resistor. VOUT2
increases when ICHARGE 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+
COMBIASALPHA
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
6325 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
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 Description Package Option Branding
AD8212YRMZ1
−40°C to +125°C 8-Lead MSOP RM-8 Y04
AD8212YRMZ-RL1
−40°C to +125°C 8-Lead MSOP, 13” Tape and Reel RM-8 Y04
AD8212YRMZ-R71
−40°C to +125°C 8-Lead MSOP, 7” Tape and Reel RM-8 Y04
AD8212WYRMZ1
−40°C to +125°C 8-Lead MSOP RM-8 Y25
AD8212WYRMZ-RL1
−40°C to +125°C 8-Lead MSOP, 13” Tape and Reel RM-8 Y25
AD8212WYRMZ-R71
−40°C to +125°C 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
©2007–2009 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D05942-0-5/09(B)