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
Current Shunt Monitor
AD8212
FUNCTIONAL BLOCK DIAGRAM
V+
1
AD8212
BIAS
CIRCUIT
COMBIASALPHA
I
OUT
Figure 1.
SENSE
8
OUTPUT
CURRENT
COMPENSATI ON
6325
05942-001
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
r
esistor 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,
ich is achieved by using an external high voltage breakdown
wh
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 compensat
ion 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. A
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Anal og Devices for its use, nor for any infringements of patents or ot her
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.
SUPPLY VOLTAGE (V+) No external pass transistor 7 65 V
With external PNP transistor
SUPPLY CURRENT2 (I
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) T
Offset Drift T
INPUT
Input Impedance
Differential 2 kΩ
Common Mode (VCM) V+ = 7 V to 65 V 5 MΩ
Voltage Range
Differential Maximum voltage between V+ and V
V
SENSE
OUTPUT
Transconductance 1000 μA/V
Current Range (I
Gain Error for T
Impedance 20 MΩ
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
T
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
TEMPERATURE RANGE
For Specified Performance (T
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 (I
differential voltage and can range from 0 μA to 500 μA. I
to the High Voltage Operation Using an External PNP Transistor section.
3
The current of the amplifier into V
for more information.
= −40°C to +125°C, TA = 25°C, unless otherwise noted.
OPR
= I
+ I
OUT
, 7 V ≤ V+ ≤ 65 V 185 200 μA
, high voltage operation 200 1000 μA
in this mode of operation is typically 185 μA and 200 μA maximum. For high voltage operation mode, refer
BIAS
(Pin 8) Current
OUT
7 V ≤ V+ ≤ 65 V, with respect to 500 μA full scale ±1 %
OPR
) T
BIAS
SUPPLY
OPR
OPR
3
V+ = 7 V to 65 V, T
) 7 V ≤ V+ ≤ 65 V, 0 mV to 500 mV differential input 500 μA
OPR
OPR
) −40 +125 °C
OPR
(Pin 8) increases when operating in high voltage mode. See the High Voltage Operation Using an External PNP Transistor section
SENSE
1
)
BIAS
7 >500 V
±3 mV
±10 μV/°C
SENSE
100 200 nA
OPR
500 mV
nV/√Hz
) added to output current (I
BIAS
). Output current varies upon input
OUT
Rev. A | Page 3 of 16
AD8212
www.BDTIC.com/ADI
ABSOLUTE MAXIMUM RATINGS
T
= −40°C to +125°C, unless otherwise noted.
OPR
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
Rev. A | Page 4 of 16
AD8212
www.BDTIC.com/ADI
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
V+ 1
AD8212
2
COM
3
BIAS
TOP VIEW
(Not to Scale)
NC 4
NC = NO CONNECT
Figure 2. Pin Configuration
8
7
6
5
V
SENSE
NC
ALPHA
I
OUT
1
2
3
05942-002
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
4 NC – –
5 I
+386 −82 Output Current.
OUT
6 ALPHA +386 +23
7 NC +386 +118
8 V
+386 +210 Noninverting Amplifier Input.
SENSE
Bias Circuit Low Side.
No Connect.
Current Compensation Circuit Input.
No Connect.
8
6
5
05942-025
Rev. A | Page 5 of 16
AD8212
V
(
V
www.BDTIC.com/ADI
TYPICAL PERFORMANCE CHARACTERISTICS
195
1200
190
T = +125°C
185
180
175
170
QUIESCENT CURRENT (µA)
165
160
5.2
5.1
5.0
4.9
REGULATOR VOLTAGE (V)
4.8
T = +25°C
5 101520 2530 35404550556065
SUPPLY VOLTAGE (V)
Figure 4. Supply Current vs. Supply (Pin V+) (I
T = +25°C
T = +125°C
5 101520 2530 35404550556065
SUPPLY VOLTAGE (V)
T = –40°C
OUT
T = –40°C
Figure 5. Regulator Voltage vs. Supply (Pin V+)
= 0 mA)
1000
800
)
µ
OS
600
INPUT
400
200
05942-005
0
–40–20020406080100120
TEMPERATURE ( °C)
05942-008
Figure 7. Input Offset Voltage vs. Temperature
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
OFFSET VO LTAGE RTI (mV )
0.2
0.1
05942-006
+125°C
+25°C
–40°C
0
7 1217222732374247525762
VOLTAGE SUPPLY (V)
05942-009
Figure 8 .Input Offset Voltage vs. Supply (Pin V+)
50
45
40
35
30
25
GAIN (dB)
20
15
10
5
0
1k10k100k1M10M
G = +50
G = +20
G = +10
FREQUENCY (Hz)
Figure 6. Gain vs. Frequency
5942-021
10
9
8
7
6
5
4
3
2
OUTPUT CURRENT DRIFT (nA/ °C)
1
0
050 100 150 200 250 300 350 400 450 500
DIFFERENTIAL INPUT VOLTAGE (mV)
Figure 9. Output Current Drift vs. Differential Input Voltage
Figure 21. Supply Range (V+) vs. Bias Resistor Value
(
High Voltage Operation)
BIAS
(k)
V+ = 100V
05942-007
05942-020
Rev. A | Page 8 of 16
AD8212
V
www.BDTIC.com/ADI
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
sistor (R
re
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
th
e 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
p
roduces 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
proportional to the input voltage (V
load current (I
output current (I
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
V
SENSE
V
OUT
V
OUT
where:
= 1000 µA/V.
g
m
In normal voltage operation mode, the bias circuit is connected
t
o GND, as shown in
185 μA throughout the 7 V to 65 V (V+) range.
) with its inverting input connected to the
SHUNT
), and, therefore, the
SENSE
) through the shunt resistor (R
LOAD
) is converted to a voltage by using an
OUT
= (gm × V
= I
LOAD
= I
OUT
= (V
× R
SENSE
SENSE
× R
× R
OUT
)
SHUNT
OUT
)/1000
Figure 22. In this mode, I
OUT
SHUNT
is typically
BIAS
) is
). The
I
BATTERY
1
R1R2
Q1
OUT
R
Figure 22. Typical Connection (7 V to 65 V Supply (Pin V+) Range)
OUT
I
OUT
R
AD8212
BIAS
CIRCUIT
SHUNT
A1
LOAD
8
OUTPUT
CURRENT
COMPENSATION
6325
LOAD
05942-003
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
ltage then remains a constant 5 V, regardless of the supply
vo
Figure 22). This regulated
(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
urrent to a voltage. Ta b le 4 provides suggested R
c
Table 4. Suggested R
Gain (V/V) R
Values
OUT
OUT
(kΩ)
values.
OUT
1 1
10 10
20
50
20
49.9
100 100
Rev. A | Page 9 of 16
AD8212
www.BDTIC.com/ADI
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 V
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.
BATTERY
1
R1R2
Q1
Q2
VOUT
R
OUT
Figure 23. High Voltage Operation Using External PNP
R
AD8212
BIAS
CIRCUIT
R
SHUNT
A1
BIAS
8
OUTPUT
CURRENT
COMPENSATI ON
6325
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
V
of one internal transistor, makes the collector of Transistor Q1
be
approximately equal to
95 V + 2(V
) = 95 V + 1.2 V = 96.2 V
be(Q2)
This voltage appears across external Transistor Q2. The voltage
ross Transistor Q1 is
ac
100 V – 96.2 V = 3.8 V
In this manner, Transistor Q2 withstands 95.6 V and the
nternal Transistor Q1 is only subjected to voltages well below
i
its breakdown capability.
break-
CE
LOAD
05942-004
In this mode of operation, the supply current (I
BIAS
) of the
AD8212 circuit increases based on the supply range and the
R
resistor chosen. For example
BIAS
if
V+ = 500 V and R
= (V+ − 5 V)/R
I
BIAS
= 500 kΩ
BIAS
BIAS
then,
I
= (500 – 5)/500 kΩ = 990 μA
BIAS
In high voltage operation, it is recommended that I
remain
BIAS
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 I
BIAS
and
V+ information when using the AD8212 in a high voltage
configuration.
When operating the AD8212, as depicted in Figure 23,
ransistor Q2 can be a FET or a bipolar PNP transistor. The
T
latter is much less expensive, however the magnitude of I
conducted to the output resistor (R
) is reduced by the
OUT
OUT
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
mpensates for the output current that is lost through the base
co
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
Because the current generated by the output compensation
cuit is equal to the base current of Transistor Q2, and the
cir
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
such that no error results from the base
OUT
current lost at Transistor Q2.
This feature of the AD8212 greatly improves I
OUT
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).
.
OUT
accuracy and
Rev. A | Page 10 of 16
AD8212
www.BDTIC.com/ADI
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
of the AD8212 is not affected.
I
LOAD
BATTERY
R
SHUNT
AD8212
V+
1
V
8
SENSE
COM
2
BIAS
3
NC
4
NOTES
1. NC = NO CONNECT.
NC
ALPHA
I
OUT
7
6
5
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
, which can be as high as 500 μA
OUT
(based on a 500 mV maximum input differential limit).
be buffered, so that the gain
OUT
LOAD
AD8661
I
R
OUT
OUT
ADC
05942-026
500 V CURRENT MONITOR
As noted in the High Voltage Operation Using an External PNP
Tr an si st o r section, the AD8212 common-mode voltage range is
tended by using an external PNP transistor. This mode of
ex
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
Z
ener 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.
I
LOAD
500V
3
4
500k
R
SHUNT
AD8212
V+1
COM2
BIAS
NC
V
SENSE
NC
ALPHA
I
OUT
LOAD
8
7
6
5
VOUT
R
OUT
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
AD8212
V+
1
V
8
SENSE
COM
2
BIAS
3
NC
4
NOTES
1. NC = NO CONNECT.
NC
ALPHA
I
OUT
7
6
5
R
OUT
Figure 25. High-Side Current Sensing for Motor Control
I
MOTOR
V
OUT
MOTOR
05942-028
NOTES
1. TRANSIST OR V
VOLTAG E MUST BE 500V.
2. NC = NO CONNECT.
BREAKDOWN
CE
05942-027
Figure 26. High Voltage Operation Using External PNP
Rev. A | Page 11 of 16
AD8212
www.BDTIC.com/ADI
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,
I
LOAD
I
CHARGE
R
SHUNT
V
1 increases as I
OUT
increases when I
flows through the shunt resistor. V
LOAD
flows through the input shunt resistor.
CHARGE
OUT
2
V
SENSE
11
BATTERY
I
OUT
R
1
OUT
AD8212
BIAS
CIRCUIT
COMBIASALPHAI
88
OUTPUT
CURRENT
COMPENSATION
6325
V
1
OUT
V
SENSE
OUTPUT
CURRENT
COMPENSATIO N
632
AD8212
BIAS
CIRCUIT
V+V+
LOAD
CHARGE
COMBIASALPHA
OUT
5
V
2
R
OUT
OUT
2
5942-011
Figure 27. Bidirectional Current Sensing
Rev. A | Page 12 of 16
AD8212
www.BDTIC.com/ADI
OUTLINE DIMENSIONS
3.20
3.00
2.80
8
5
3.20
3.00
1
2.80
PIN 1
0.65 BSC
0.95
0.85
0.75
0.15
0.38
0.00
0.22
COPLANARITY
0.10
COMPLIANT TO JEDEC STANDARDS MO-187-AA
Figure 28. 8-Lead Mini Small Outline Package [MSOP]
ORDERING GUIDE
Model Temperature Range Package Description Package Option Branding
AD8212YRMZ
AD8212YRMZ-RL
AD8212YRMZ-R7
1
Z = RoHS Compliant Part.
1
1
1
−40°C to +125°C 8-Lead MSOP RM-8 Y04
−40°C to +125°C 8-Lead MSOP, 13” Tape and Reel RM-8 Y04
−40°C to +125°C 8-Lead MSOP, 7” Tape and Reel RM-8 Y04