AD8205

AD8205
Single-Supply 42 V System
Difference Amplifier
AD8205
Ideal for current shunt applications
High common-mode voltage range
−2 V to +65 V operating
−5 V to +68 V survival
Gain = 50
Wide operating temperature range
Die: −40°C to +150°C
8-lead SOIC: −40°C to +125°C
Adjustable offset
Available in SOIC and die form
EXCELLENT AC AND DC PERFORMANCE
15 µV/°C offset drift
30 ppm/°C gain drift
80 dB CMRR dc to 20 kHz
FUNCTIONAL BLOCK DIAGRAM
V+
6
+IN 8
5
OUT
7
VREF1
3
VREF2
–IN 1
AD8205
NC 4
2
NC = NO CONNECT
GND
04315-0-001
FEATURES
Figure 1.
APPLICATIONS
High-side current sensing in:
Motor controls
Transmission controls
Diesel injection controls
Engine management
Suspension controls
Vehicle dynamic controls
DC-to-dc converters
GENERAL DESCRIPTION
The AD8205 is a single-supply difference amplifier for amplifying small differential voltages in the presence of large commonmode 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 die and packaged form. The operating
temperature range for the die is 25°C higher (up to 150°C) than
the packaged part to enable the user to apply the AD8205 in
high temperature applications.
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.
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: 781.326.8703
© 2004 Analog Devices, Inc. All rights reserved.
AD8205
TABLE OF CONTENTS
Specifications..................................................................................... 3
Bidirectional Operation................................................................9
Absolute Maximum Ratings............................................................ 4
External Reference Output........................................................ 10
ESD Caution.................................................................................. 4
Splitting the Supply .................................................................... 10
Pin Configuration and Function Descriptions............................. 5
Splitting an External Reference ................................................ 10
Typical Performance Characteristics ............................................. 6
Applications..................................................................................... 11
Theory of Operation ........................................................................ 8
High-Side Current Sense with a Low-Side Switch................. 11
Output Offset Adjustment............................................................... 9
High-Side Current Sense with a High-Side Switch ............... 11
Unidirectional Operation............................................................ 9
Outline Dimensions ....................................................................... 12
Ground Referenced Output ........................................................ 9
Ordering Guide .......................................................................... 12
V+ Referenced Output................................................................. 9
REVISION HISTORY
4/04—Revision 0: Initial Version
Rev. 0 | Page 2 of 12
AD8205
SPECIFICATIONS
TA = Operating Temperature Range, VS = 5 V, unless otherwise noted.
Table 1.
Parameter
GAIN
Initial
Accuracy
Accuracy Over Temperature
Gain vs. Temperature
VOLTAGE OFFSET
Offset Voltage (RTI)
Over Temperature (RTI)
Offset Drift
INPUT
Input Impedance
Differential
Common Mode
Input Voltage Range
Common-Mode Rejection
OUTPUT
Output Voltage Range
Output Resistance
DYNAMIC RESPONSE
Small Signal −3 dB Bandwidth
Slew Rate
NOISE
0.1 Hz to 10 Hz, RTI
Spectral Density, 1 kHz, RTI
OFFSET ADJUSTMENT
Ratiometric Accurancy3
Accuracty, RTO
Output Offset Adjustment Range
VREF Divider Resistor Values
POWER SUPPLY
Operating Range
Quiescent Current Over Temperature
Power Supply Rejection Ratio
Temperature Range
For Specified Performance
AD8205 SOIC
Min
Typ Max
Conditions
Min
AD8205 DIE
Typ Max
50
VO ≥ 0.1 V dc, 25°C
Specified Temperature Range
50
±1
±1.2
±1
±1.3
±30
25°C
Specified Temperature Range
Common Mode, Continuous
Differential1
25°C, f = DC to 20 kHz2
Operating Temperature Range,
f = DC to 20 kHz2
RL = 25 kΩ
±2
±4.5
15
400
200
400
200
−2
78
76
65
100
86
80
4.5
VO = 0.1 V dc
78
76
4.8
1
−40
50
0.5
50
0.5
kHz
V/µs
20
0.5
20
0.5
µV p-p
µV/√Hz
32
Rev. 0 | Page 3 of 12
0.05
0.503
±2
0.497
4.8
40
0.05
24
5.5
2
4.5
4.8
kΩ
kΩ
V
mV
dB
dB
V
Ω
32
0.503
±2
V/V
mV/V
4.8
40
V
kΩ
5.5
2
V
mA
dB
+150
°C
70
+125
Input voltage range = ±50 mV with half-scale offset.
Source imbalance < 2 Ω.
3
The offset adjustment is ratiometric to the power supply when VREF1 and VREF2 are used as a divider between the supplies.
2
65
100
86
80
mV
mV
µV/°C
200
70
Operating Temperature Range
−2
V/V
%
%
ppm/°C
200
0.497
0.05
24
±2.5
±6
15
0.05
Divider to Supplies
Voltage applied to VREF1 and VREF2
in Parallel
VS = 5 V
±30
Unit
−40°C
AD8205
ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter
Supply Voltage
Continuous Input Voltage
Reverse Supply Voltage
Operating Temperature Range
Storage Temperature
Output Short-Circuit Duration
Rating
12.5 V
−5 V to +68 V
0.3 V
−40°C to +125°C
−65 to +150C
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
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on
the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or
loss of functionality.
Rev. 0 | Page 4 of 12
AD8205
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
–IN 1
8
AD8205
+IN
VREF1
TOP VIEW
6 V+
(Not to Scale)
NC 4
5 OUT
GND 2
7
NC = NO CONNECT
04315-0-026
VREF2 3
Figure 3. Pin Configuration
04315-0-002
Table 3. Pin Function Descriptions
Figure 2. Metallization Diagram
Pin No.
1
2
3
4
5
6
7
8
Mnemonic
−IN
GND
VREF2
NC
OUT
V+
VREF1
+IN
X
−206
−447
−432
N/A
444
444
456
203
Y
508
57
−457
N/A
−472
−203
434
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+.
Rev. 0 | Page 5 of 12
AD8205
TYPICAL PERFORMANCE CHARACTERISTICS
500
40
400
35
300
30
25
100
GAIN (dB)
VOSI (µV)
200
TYP. VOSI (DIE)
0
–100
TYP. VOSI (SOIC)
–200
20
15
10
–400
–500
–40
–20
0
20
40
60
80
TEMPERATURE (°C)
100
120
04315-0-008
04315-0-003
–300
5
0
10
140
Figure 4. Typical Offset Drift
100
1k
10k
FREQUENCY (Hz)
100k
1M
Figure 7. Typical Small Signal Bandwidth (VOUT = 200 mV p-p)
120
110
100
50mV/DIV
90
CMR (dB)
80
70
60
50
40
30
04315-0-005
10
0
10
04315-0-024
1V/DIV
20
100
1k
10k
100k
FREQUENCY (Hz)
1M
40µs/DIV
10M
Figure 8. Rise/Fall Time
Figure 5. CMR vs. Frequency
12000
100mV/DIV
10000
8000
4000
2000
TYP. IN SOIC
0
2V/DIV
–2000
–4000
TYP. DIE
–6000
04315-0-007
–8000
–10000
–12000
–40
04315-0-021
GAIN ERROR (ppm)
6000
–20
0
20
40
60
80
TEMPERATURE (°C)
100
120
2µs/DIV
140
Figure 9. Differential Overload Recovery (Falling)
Figure 6. Gain Drift
Rev. 0 | Page 6 of 12
AD8205
50V/DIV
100mV/DIV
50mV/DIV
04315-0-023
04315-0-022
2V/DIV
2µs/DIV
1µs/DIV
Figure 10. Differential Overload Recovery (Rising)
Figure 12. Common-Mode Response
2V/DIV
04315-0-025
0.01%/DIV
40µs/DIV
Figure 11. Settling Time
Rev. 0 | Page 7 of 12
AD8205
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 commonmode voltages. It is offered in both packaged and die form.
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 die temperature range is −40°C
to +150°C with a guaranteed gain accuracy of 1.3%.
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 die input offset is less than 6 mV referred to the input over the die operating
temperature range.
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.
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.
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 common-mode rejection ratio
over the operating temperature is 76 dB for both the die and
packaged part.
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 output offset can be adjusted from 0.05 V to 4.8 V (V+ =
5 V) for unipolar and bipolar operation.
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 AD8205 consists of two amplifiers (A1 and A2), a resistor
network, small voltage reference, and a bias circuit (not shown),
see Figure 13.
The output stage is Class A with a PNP pull-up transistor and a
300 µA current sink pull-down.
–IN
RA
+IN
RA
A1
RB
RB
RC
RC
250mV
RF
RF
RD
RD
A2
AD8205
RE
RF
VOUT
VREF1
RREF
RREF
GND
VREF2
Figure 13. Simplified Schematic
Rev. 0 | Page 8 of 12
04315-0-012
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%.
AD8205
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.
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).
V+
+IN
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.
OUT
–IN
VREF1
AD8205
NC
VREF2
04315-0-014
GND
NC = NO CONNECT
Figure 15. V+ Referenced Output
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).
Table 5. V+ = 5 V
VIN (Referred to −IN)
0V
100 mV
VO
4.8 V
0.05 V
V+
+IN
BIDIRECTIONAL OPERATION
OUT
–IN
Bidirectional operation allows the AD8205 to measure currents
through a resistive shunt in two directions.
VREF1
AD8205
NC
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.
VREF2
04315-0-013
GND
NC = NO CONNECT
Figure 14. Ground Referenced Output
Table 4. V+ = 5 V
VIN (Referred to −IN)
0V
100 mV
VO
0.05 V
4.8 V
Table 6. V+ = 5 V, VO = 2.5 with VIN = 0 V
VIN (Referred to −IN)
+40 mV
−40 mV
VO
4.5 V
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.
Rev. 0 | Page 9 of 12
AD8205
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.
V+
+IN
OUT
–IN
VREF1
AD8205
V+
+IN
OUT
–IN
NC
VREF2
VREF1
AD8205
04315-0-016
GND
NC = NO CONNECT
2.5V VOLTAGE
REFERENCE
Figure 17. Split Supply
GND
SPLITTING AN EXTERNAL REFERENCE
VREF2
NC = NO CONNECT
04315-0-015
NC
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).
Figure 16. External Reference Output
SPLITTING THE SUPPLY
V+
+IN
OUT
–IN
VREF1
AD8205
NC
GND
VOLTAGE
REFERENCE
VREF2
NC = NO CONNECT
Figure 18. Split External Reference
Rev. 0 | Page 10 of 12
5V
04315-0-017
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.
AD8205
APPLICATIONS
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.
When using a high-side switch, the battery voltage is connected
to the load when the switch is closed, causing the commonmode 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 voltage to be held one
diode drop below ground by the clamp diode.
5V
HIGH-SIDE CURRENT SENSE WITH A LOW-SIDE
SWITCH
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.
5V
42V
BATTERY
INDUCTIVE
LOAD
+IN VREF1 +VS
OUT
AD8205
SHUNT
–IN
OUT
AD8205
–IN
CLAMP
DIODE
GND VREF2 NC
04315-0-019
INDUCTIVE
LOAD
NC = NO CONNECT
Figure 20. High-Side Switch
Another typical application for the AD8205 is as part of the
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 solution
than a ground referenced op amp because ground is not typically a stable reference voltage in this type of application. This
instability in the ground reference causes the measurements
that could be made with a simple ground referenced op amp to
be inaccurate.
The AD8205 measures current in both directions as the
H-bridge switches and the motor changes direction. The output
of the AD8205 is configured in an external reference bidirectional mode, see the Output Offset Adjustment section.
GND VREF2 NC
04315-0-018
SWITCH
NC = NO CONNECT
+IN VREF1 +VS
SHUNT
CONTROLLER
5V
Figure 19. Low-Side Switch
HIGH-SIDE CURRENT SENSE WITH A HIGH-SIDE
SWITCH
MOTOR
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.
Rev. 0 | Page 11 of 12
+IN VREF1 +VS
OUT
AD8205
SHUNT
–IN
GND VREF2 NC
5V
2.5V
NC = NO CONNECT
Figure 21. Motor Control Application
04315-0-020
CLAMP
DIODE
42V
BATTERY
AD8205
OUTLINE DIMENSIONS
5.00 (0.1968)
4.80 (0.1890)
8
4.00 (0.1574)
3.80 (0.1497) 1
5
1.27 (0.0500)
BSC
0.25 (0.0098)
0.10 (0.0040)
6.20 (0.2440)
4 5.80 (0.2284)
1.75 (0.0688)
1.35 (0.0532)
0.51 (0.0201)
COPLANARITY
SEATING 0.31 (0.0122)
0.10
PLANE
0.50 (0.0196)
× 45°
0.25 (0.0099)
8°
0.25 (0.0098) 0° 1.27 (0.0500)
0.40 (0.0157)
0.17 (0.0067)
COMPLIANT TO JEDEC STANDARDS MS-012AA
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
Figure 22. 8-Lead Standard Small Outline Package [SOIC]
Narrow Body
(R-8)
Dimensions shown in millimeters and (inches)
ORDERING GUIDE
Models
AD8205YR
AD8205YR-REEL
AD8205YR-REEL7
AD8205YCSURF
Temperature Range
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +150°C
Package Description
8-Lead SOIC
8-Lead SOIC, 13” Tape and Reel
8-Lead SOIC, 7” Tape and Reel
Die Form
© 2004 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners.
D04315–0–4/04(0)
Rev. 0 | Page 12 of 12
Package Option
R-8
R-8
R-8
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