Single-Supply 42 V System
Difference Amplifier
AD8205
Rev. B
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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
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Trademarks and registered trademarks are the property of their respective owners.
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Fax: 781.461.3113 ©2004–2010 Analog Devices, Inc. All rights reserved.
FEATURES
Ideal for current shunt applications
High common-mode voltage range
−2 V to +65 V operating
−25 V to +75 V survival
Gain = 50
Wide operating temperature range: −40°C to +125°C
Bidirectional operation
Available in 8 Lead SOIC
Qualified for automotive applications
EXCELLENT AC AND DC PERFORMANCE
15 μV/°C offset drift
30 ppm/°C gain drift
80 dB CMRR dc to 20 kHz
APPLICATIONS
High-side current sensing in:
Motor controls
Transmission controls
Diesel injection controls
Engine management
Suspension controls
Vehicle dynamic controls
DC-to-dc converters
FUNCTIONAL BLOCK DIAGRAM
04315-0-001
AD8205
8
1
4
2
3
7
5
6
+IN
–IN
NC
NC = NO CONNECT GND
V+
OUT
V
REF
1
V
REF
2
Figure 1.
GENERAL DESCRIPTION
The AD8205 is a single-supply difference amplifier for
amplifying small differential voltages in the presence of large
common-mode voltages. The operating input common-mode
voltage range extends from −2 V to +65 V. The typical single-
supply voltage is 5 V.
The AD8205 is offered in an 8-Lead SOIC package and rated for
operation from −40°C to +125°C.
Excellent dc performance over temperature keeps errors in the
measurement loop to a minimum. Offset drift is typically less
than 15 μV/°C, and gain drift is typically below 30 ppm/°C.
The output offset can be adjusted from 0.05 V to 4.8 V with a
5 V supply by using the VREF1 and VREF2 pins. With VREF1
attached to the V+ pin, and VREF2 attached to the GND pin, the
output is set at half scale. Attaching both pins to GND causes
the output to be unipolar, starting near ground. Attaching both
pins to V+ causes the output to be unipolar starting near V+.
Other offsets can be obtained by applying an external voltage to
the VREF1 and VREF2 pins.
AD8205
Rev. B | Page 2 of 12
TABLE OF CONTENTS
Features .............................................................................................. 1
Excellent AC and DC Performance ................................................ 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 ........................................................................ 8
Output Offset Adjustment ............................................................... 9
Unidirectional Operation .............................................................9
Ground Referenced Output .........................................................9
V+ Referenced Output .................................................................9
Bidirectional Operation ................................................................9
External Reference Output ........................................................ 10
Splitting the Supply .................................................................... 10
Splitting an External Reference ................................................ 10
Applications Information .............................................................. 11
High-Side Current Sense with a Low-Side Switch ................. 11
High-Side Current Sense with a High-Side Switch ............... 11
Outline Dimensions ....................................................................... 12
Ordering Guide .......................................................................... 12
Automotive Products ................................................................. 12
REVISION HISTORY
7/10—Rev. A to Rev. B
Changes to Features Section and General Description Section . 1
Delete Die Columns, Table 1 ........................................................... 3
Changes to Table 2 ............................................................................ 4
Changes to Figure 4 and Figure 6 ................................................... 6
Changes to Theory of Operation Section ...................................... 8
Changes to Ordering Guide .......................................................... 12
Added Automotive Products Section .......................................... 12
10/09—Rev. 0 to Rev. A
Changes to Output Resistance Parameter, Table 1 ....................... 3
Updated Outline Dimensions ....................................................... 12
Changes to Ordering Guide .......................................................... 12
4/04—Revision 0: Initial Version
AD8205
Rev. B | Page 4 of 12
ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Rating
Supply Voltage 12.5 V
Continuous Input Voltage −25 V to +75 V
Input Transient Survival −30 V to +80 V
Differential Input Survival −25 V to +75 V
Reverse Supply Voltage 0.3 V
Operating Temperature Range −40°C to +125°C
Storage Temperature −65 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 and 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
AD8205
Rev. B | Page 5 of 12
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
04315-0-002
Figure 2. Metallization Diagram
NC = NO CONNECT
AD8205
TOP VIEW
(Not to Scale)
–IN
1
GND
2
V
REF
2
3
NC
4
+IN
V
REF
1
V+
OUT
8
7
6
5
04315-0-026
Figure 3. Pin Configuration
Table 3. Pin Function Descriptions
Pin No. Mnemonic X Y
1 −IN −206 508
2 GND −447 57
3 VREF2 −432 −457
4 NC N/A N/A
5 OUT 444 −472
6 V+ 444 −203
7 VREF1 456 434
8 +IN 203 509
Die size is 1170 μm by 1280 μm.
Die thickness is 13 mil.
Minimum passivation opening (minimum bond pad size) is
92 μm × 92 μm.
Passivation type is 8KA USG (Oxide) + 10KA Oxynitride.
Bond pad metal composition is 98.5% Al, 1% Si, and 0.5% Cu.
Backside potential is V+.
AD8205
Rev. B | Page 6 of 12
TYPICAL PERFORMANCE CHARACTERISTICS
500
–500
–400
–300
–200
–100
0
100
200
300
400
–40 –20 0 20 40 60 80 100 120 140
04315-0-003
TEMPERATURE (°C)
VOSI (μV)
TYP. VOSI (SOIC)
Figure 4. Typical Offset Drift
120
0
10
20
30
40
50
60
70
80
90
100
110
10 100 1k 10k 100k 1M 10M
04315-0-005
FREQUENCY (Hz)
CMR (dB)
Figure 5. CMR vs. Frequency
12000
–12000
–10000
–8000
–6000
–4000
–2000
0
2000
4000
6000
8000
10000
–40 –20 0 20 40 60 80 100 120 140
04315-0-007
TEMPERATURE (°C)
GAI N ERRO R (p p m )
TYP. IN SOIC
Figure 6. Gain Drift
40
0
5
10
15
20
25
30
35
10 100 1k 10k 100k 1M
04315-0-008
FREQUENCY (Hz)
GAIN (dB)
Figure 7. Typical Small Signal Bandwidth (VOUT = 200 mV p-p)
04315-0-024
40μs/DIV
1V/DIV
50mV/DIV
Figure 8. Rise/Fall Time
04315-0-021
2μs/DIV
2V/DIV
100mV/DIV
Figure 9. Differential Overload Recovery (Falling)
AD8205
Rev. B | Page 7 of 12
04315-0-022
2μs/DIV
2V/DIV
100mV/DIV
Figure 10. Differential Overload Recovery (Rising)
04315-0-025
40μs/DIV
2V/DIV
0.01%/DIV
Figure 11. Settling Time
04315-0-023
1μs/DIV
50V/DIV
50mV/DIV
Figure 12. Common-Mode Response
AD8205
Rev. B | Page 8 of 12
THEORY OF OPERATION
The AD8205 is a single-supply difference amplifier that uses a
unique architecture to accurately amplify small differential
current shunt voltages in the presence of rapidly changing
common-mode voltages.
In typical applications, the AD8205 is used to measure current
by amplifying the voltage across a current shunt placed across
the inputs.
The gain of the AD8205 is 50 V/V, with an accuracy of 1.2%.
This accuracy is guaranteed over the operating temperature
range of −40°C to +125°C.
The input offset is less than 2 mV referred to the input at 25°C,
and 4.5 mV maximum referred to the input over the full
operating temperature range for the packaged part.
The AD8205 operates with a single supply from 4.5 V to
10 V (absolute maximum = 12.5 V). The supply current is
less than 2 mA.
High accuracy trimming of the internal resistors allows the
AD8205 to have a common-mode rejection ratio better than
78 dB from dc to 20 kHz.
The output offset can be adjusted from 0.05 V to 4.8 V (V+ = 5 V)
for unipolar and bipolar operation.
The AD8205 consists of two amplifiers (A1 and A2), a resistor
network, small voltage reference, and a bias circuit (not shown),
see Figure 13.
The set of input attenuators preceding A1 consist of RA, RB, and
RC, which reduce the common-mode voltage to match the input
voltage range of A1. The two attenuators form a balanced bridge
network. When the bridge is balanced, the differential voltage
created by a common-mode voltage is 0 V at the inputs of A1.
The input attenuation ratio is 1/16.7. The combined series
resistance of RA, RB, and RC is approximately 200 kΩ ± 20%.
By attenuating the voltages at Pin 1 and Pin 8, the A1 amplifier
inputs are held within the power supply range, even if Pin 1 and
Pin 8 exceed the supply or fall below common (ground). A
reference voltage of 250 mV biases the attenuator above ground.
This allows the amplifier to operate in the presence of negative
common-mode voltages.
The input network also attenuates normal (differential) mode
voltages. A1 amplifies the attenuated signal by 26. The input
and output of this amplifier are differential to maximize the ac
common-mode rejection.
A2 converts the differential voltage from A1 into a single-ended
signal and provides further amplification. The gain of this
second stage is 32.15.
The reference inputs, VREF1 and VREF2, are tied through resistors
to the positive input of A2, which allows the output offset to be
adjusted anywhere in the output operating range. The gain is
1 V/V from the reference pins to the output when the reference
pins are used in parallel. The gain is 0.5 V/V when they are used
to divide the supply.
The ratios of Resistors RA, RB, RC, RD, and RF are trimmed to a
high level of precision to allow the common-mode rejection
ratio to exceed 80 dB. This is accomplished by laser trimming
the resistor ratio matching to better than 0.01%.
The total gain of 50 is made up of the input attenuation of
1/16.7 multiplied by the first stage gain of 26 and the second
stage gain of 32.15.
The output stage is Class A with a PNP pull-up transistor and a
300 μA current sink pull-down.
04315-0-012
AD8205
+IN
–
IN
250mV
GND
A1
A2
RARA
RBRBRFRFRDRD
RERF
RCRCVOUT
RREF
RREF
VREF1
VREF2
Figure 13. Simplified Schematic
AD8205
Rev. B | Page 9 of 12
OUTPUT OFFSET ADJUSTMENT
The output of the AD8205 can be adjusted for unidirectional or
bidirectional operation.
UNIDIRECTIONAL OPERATION
Unidirectional operation allows the AD8205 to measure
currents through a resistive shunt in one direction. The basic
modes for unidirectional operation are ground referenced
output mode and V+ referenced output mode.
In the case of unidirectional operation, the output could be set
at the negative rail (near ground) or at the positive rail (near
V+) when the differential input is 0 V. The output moves to the
opposite rail when a correct polarity differential input voltage is
applied. In this case, full scale is approximately 100 mV. The
required polarity of the differential input depends on the output
voltage setting. If the output is set at the positive rail, the input
polarity needs to be negative to move the output down. If the
output is set at ground, the polarity is positive to move the
output up.
GROUND REFERENCED OUTPUT
When using the AD8205 in this mode, both reference inputs are
tied to ground, which causes the output to sit at the negative rail
when there are zero differential volts at the input (see Figure 14).
04315-0-013
AD8205
+IN
–IN
NC
NC = NO CONNECT
GND
V+
OUT
V
REF
1
V
REF
2
Figure 14. Ground Referenced Output
Table 4. V+ = 5 V
VIN (Referred to −IN) VO
0 V 0.05 V
100 mV 4.8 V
V+ REFERENCED OUTPUT
This mode is set when both reference pins are tied to the
positive supply. It is typically used when the diagnostic scheme
requires detection of the amplifier and the wiring before power
is applied to the load (see Figure 15).
04315-0-014
AD8205
+IN
–IN
NC
NC = NO CONNECT
GND
V+
OUT
V
REF
1
V
REF
2
Figure 15. V+ Referenced Output
Table 5. V+ = 5 V
VIN (Referred to −IN) VO
0 V 4.8 V
100 mV 0.05 V
BIDIRECTIONAL OPERATION
Bidirectional operation allows the AD8205 to measure currents
through a resistive shunt in two directions.
In this case, the output is set anywhere within the output range.
Typically, it is set at half-scale for equal range in both directions.
In some cases, however, it is set at a voltage other than half-scale
when the bidirectional current is nonsymmetrical.
Table 6. V+ = 5 V, VO = 2.5 with VIN = 0 V
VIN (Referred to −IN) VO
+40 mV 4.5 V
−40 mV 0.5 V
Adjusting the output is accomplished by applying voltage(s) to
the reference inputs.
VREF1 and VREF2 are tied to internal resistors that connect to an
internal offset node. There is no operational difference between
the pins.
AD8205
Rev. B | Page 10 of 12
EXTERNAL REFERENCE OUTPUT
Tying both pins together and to a reference produces an output
at the reference voltage when there is no differential input (see
Figure 16). The output moves down from the reference voltage
when the input is negative relative to the −IN pin and up when
the input is positive relative to the −IN pin.
04315-0-015
AD8205
+IN
–IN
NC
NC = NO CONNECT
GND
V+
OUT
V
REF
1
V
REF
2
2.5V VOLTAGE
REFERENCE
Figure 16. External Reference Output
SPLITTING THE SUPPLY
By tying one reference pin to V+ and the other to the ground
pin, the output is set at half of the supply when there is no
differential input (see Figure 17). The benefit is that no external
reference is required to offset the output for bidirectional
current measurement. This creates a midscale offset that is
ratiometric to the supply, which means that if the supply increases
or decreases, the output remains at half the supply. For example, if
the supply is 5.0 V, the output is at half scale or 2.5 V. If the supply
increases by 10% (to 5.5 V), the output goes to 2.75 V.
04315-0-016
AD8205
+IN
–IN
NC
NC = NO CONNECT
GND
V+
OUT
V
REF
1
V
REF
2
Figure 17. Split Supply
SPLITTING AN EXTERNAL REFERENCE
In this case, an external reference is divided by 2 with an
accuracy of approximately 0.5% by connecting one VREF pin to
ground and the other VREF pin to the reference (see Figure 18).
04315-0-017
AD8205
+IN
–IN
NC
NC = NO CONNECT
GND
V+
OUT
V
REF
1
V
REF
2
5V VOLTAGE
REFERENCE
Figure 18. Split External Reference
AD8205
Rev. B | Page 11 of 12
APPLICATIONS INFORMATION
A typical application for the AD8205 is high-side measurement
of a current through a solenoid for PWM control of the
solenoid opening. Typical applications include hydraulic
transmission control and diesel injection control.
Two typical circuit configurations are used for this type of
application.
HIGH-SIDE CURRENT SENSE WITH A LOW-SIDE
SWITCH
In this case, the PWM control switch is ground referenced. An
inductive load (solenoid) is tied to a power supply. A resistive
shunt is placed between the switch and the load (see Figure 19).
An advantage of placing the shunt on the high side is that the
entire current, including the re-circulation current, can be
measured since the shunt remains in the loop when the switch
is off. In addition, diagnostics can be enhanced because shorts
to ground can be detected with the shunt on the high side.
In this circuit configuration, when the switch is closed, the
common-mode voltage moves down to near the negative rail.
When the switch is opened, the voltage reversal across the
inductive load causes the common-mode voltage to be held one
diode drop above the battery by the clamp diode.
04315-0-018
+IN V
REF
1 +V
S
OUT
–IN GND V
REF
2 NC
INDUCTIVE
LOAD
AD8205
CLAMP
DIODE
42V
BATTER
Y
SHUNT
SWITCH
NC = NO CONNECT
5V
Figure 19. Low-Side Switch
HIGH-SIDE CURRENT SENSE WITH A HIGH-SIDE
SWITCH
This configuration minimizes the possibility of unexpected
solenoid activation and excessive corrosion (see Figure 20). In
this case, both the switch and the shunt are on the high side.
When the switch is off, this removes the battery from the load,
which prevents damage from potential shorts to ground, while
still allowing the recirculating current to be measured and
providing for diagnostics. Removing the power supply from the
load for the majority of the time minimizes the corrosive effects
that could be caused by the differential voltage between the load
and ground.
When using a high-side switch, the battery voltage is connec
to the load when the switch is closed, causing the common-
mode voltage to increase to the battery voltage. In this case
when the switch is opened, the voltage reversal across the
inductive load causes the common-mode volta
ted
,
ge to be held one
diode drop below ground by the clamp diode.
04315-0-019
+IN VREF1 +VSOUT
–IN GND VREF2 NC
INDUCTIVE
LOAD
AD8205
CLAMP
DIODE
42V
BATTER
Y
SHUNT
SWITCH
NC = NO CONNECT
5V
he
tion
plication.
th a simple ground
he output
bidirectional mode, see the Output Offset Adjustment section.
Figure 20. High-Side Switch
Another typical application for the AD8205 is as part of t
control loop in H-bridge motor control. In this case, the
AD8205 is placed in the middle of the H-bridge (see Figure 21)
so that it can accurately measure current in both directions by
using the shunt available at the motor. This is a better solu
than a ground referenced op amp because ground is not
typically a stable reference voltage in this type of ap
This instability in the ground reference causes the
measurements that could be made wi
referenced op amp to be inaccurate.
The AD8205 measures current in both directions as the
H-bridge switches and the motor changes direction. T
of the AD8205 is configured in an external reference
04315-0-020
+IN V
REF
1 +V
S
OUT
–IN GND V
REF
2 NC
AD8205
SHUNT
5V
2.5V
5V
CONTROLLER
MOTOR
NC = NO CONNECT
Figure 21. Motor Control Application
AD8205
Rev. B | Page 12 of 12
OUTLINE DIMENSIONS
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
COMPLIANT TO JEDEC STANDARDS MS-012-AA
012407-A
0.25 (0.0098)
0.17 (0.0067)
1.27 (0.0500)
0.40 (0.0157)
0.50 (0.0196)
0.25 (0.0099) 45°
8°
0°
1.75 (0.0688)
1.35 (0.0532)
SEATING
PLANE
0.25 (0.0098)
0.10 (0.0040)
4
1
85
5.00(0.1968)
4.80(0.1890)
4.00 (0.1574)
3.80 (0.1497)
1.27 (0.0500)
BSC
6.20 (0.2441)
5.80 (0.2284)
0.51 (0.0201)
0.31 (0.0122)
COPLANARITY
0.10
Figure 22. 8-Lead Standard Small Outline Package [SOIC_N]
Narrow Body
(R-8)
Dimensions shown in millimeters and (inches)
ORDERING GUIDE
Model1, 2 Temperature Range Package Description Package Option
AD8205YR −40°C to +125°C 8-Lead SOIC_N R-8
AD8205YR-REEL −40°C to +125°C 8-Lead SOIC_N, 13” Tape and Reel R-8
AD8205YR-REEL7 −40°C to +125°C 8-Lead SOIC_N, 7” Tape and Reel R-8
AD8205YRZ −40°C to +125°C 8-Lead SOIC_N R-8
AD8205YRZ-RL −40°C to +125°C 8-Lead SOIC_N, 13” Tape and Reel R-8
AD8205YRZ-R7 −40°C to +125°C 8-Lead SOIC_N, 7” Tape and Reel R-8
AD8205WYRZ −40°C to +125°C 8-Lead SOIC_N R-8
AD8205WYRZ-RL −40°C to +125°C 8-Lead SOIC_N, 13” Tape and Reel R-8
AD8205WYRZ-R7 −40°C to +125°C 8-Lead SOIC_N, 7” Tape and Reel R-8
1 Z = RoHS Compliant Part.
2 W = Qualified for Automotive Applications.
AUTOMOTIVE PRODUCTS
The AD8205WYRZ models are available with controlled manufacturing to support the quality and reliability requirements of automotive
applications. Note that these automotive models may have specifications that differ from the commercial models; therefore, designers
should review the Specifications section of this data sheet carefully. Only the automotive grade products shown are available for use in
automotive applications. Contact your local Analog Devices account representative for specific product ordering information and to
obtain the specific Automotive Reliability reports for these models.
©2004–2010 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D04315-0-7/10(B)
