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Single-Supply 42 V System

Difference Amplifier

AD8205

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

FEATURES

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

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

+IN

IN

NC = NO CONNECT

GND

V+

OUT

REF

Figure 1.

GENERAL DESCRIPTION

The AD8205 is a single-supply difference amplifier for amplify-
ing 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 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 V

REF

1 and V

REF

2 pins. With V

REF

1 at-

tached to the V+ pin, and V

REF

2 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 V

REF

1 and V

REF

2 pins.

AD8205

Rev. 0 | Page 2 of 12

TABLE OF CONTENTS

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..................................................................................... 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

REVISION HISTORY

4/04--Revision 0: Initial Version

AD8205

Rev. 0 | Page 3 of 12

SPECIFICATIONS

= Operating Temperature Range, V

= 5 V, unless otherwise noted.

Table 1.

AD8205 SOIC

AD8205 DIE

Parameter Conditions

Min Typ Max Min Typ Max Unit

GAIN

Initial

V/V

Accuracy V

0.1 V dc, 25°C

±1

Accuracy Over Temperature

Specified Temperature Range

±1.2

±1.3

Gain

vs.

Temperature

±30

ppm/°C

VOLTAGE

OFFSET

Offset Voltage (RTI)

25°C

±2

±2.5

Over Temperature (RTI)

Specified Temperature Range

±4.5

±6

Offset

Drift

µV/°C

INPUT

Input

Impedance

Differential

400

Common

Mode

200

Input Voltage Range

Common Mode, Continuous

-2

65 -2 65 V

Differential

100

Common-Mode Rejection

25°C, f = DC to 20 kHz

78 86

Operating Temperature Range,
f = DC to 20 kHz

76 80

OUTPUT

Output Voltage Range

= 25 k

0.05

4.8

0.05

4.8

Output

Resistance

200

DYNAMIC

RESPONSE

Small Signal -3 dB Bandwidth

kHz

Slew

Rate

0.5

V/µs

NOISE

0.1 Hz to 10 Hz, RTI

µV p-p

Spectral Density, 1 kHz, RTI

0.5

µV/Hz

OFFSET

ADJUSTMENT

Ratiometric Accurancy

Divider

Supplies

0.497

0.503 0.497

0.503 V/V

Accuracty, RTO

Voltage applied to V

REF

1 and V

REF

in Parallel

±2

mV/V

Output Offset Adjustment Range

= 5 V

0.05

4.8

0.05

4.8

VREF Divider Resistor Values

POWER

SUPPLY

Operating

Range

4.5 5.5 4.5 5.5 V

Quiescent Current Over Temperature

= 0.1 V dc

Power Supply Rejection Ratio

Temperature

Range

For Specified Performance

Operating Temperature

Range

-40

+125

-40°C

+150

°C

Input voltage range = ±50 mV with half-scale offset.

Source imbalance < 2 .

The offset adjustment is ratiometric to the power supply when V

REF

1 and V

REF

2 are used as a divider between the supplies.

AD8205

Rev. 0 | Page 4 of 12

ABSOLUTE MAXIMUM RATINGS

Table 2.

Parameter Rating

Supply Voltage

12.5 V

Continuous Input Voltage

-5 V to +68 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

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 pro-
prietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electro-
static discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or
loss of functionality.

AD8205

Rev. 0 | 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

GND

REF

+IN

REF

V+

OUT

04315-0-026

Figure 3. Pin Configuration

Table 3. Pin Function Descriptions

Pin No.

Mnemonic

1 -IN

-206

508

2 GND

-447

3 V

REF

2 -432

-457

4 NC

N/A

5 OUT

444

-472

6 V+

444

-203

7 V

REF

1 456

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. 0 | Page 6 of 12

TYPICAL PERFORMANCE CHARACTERISTICS

500

400

300

200

100

200

300

400

40

20

100

120

140

04315-0-003

TEMPERATURE (

°C)

OSI

(

µ
V)

TYP. V

OSI

(SOIC)

TYP. V

OSI

(DIE)

Figure 4. Typical Offset Drift

120

100

110

100

10k

100k

10M

04315-0-005

FREQUENCY (Hz)

CMR (dB)

Figure 5. CMR vs. Frequency

12000

10000

8000

6000

4000

2000

4000

6000

8000

10000

40

20

100

120

140

04315-0-007

TEMPERATURE (

°C)

GAIN ERROR (

ppm)

TYP. DIE

TYP. IN SOIC

Figure 6. Gain Drift

100

10k

100k

04315-0-008

FREQUENCY (Hz)

GAIN (

Figure 7. Typical Small Signal Bandwidth (V

OUT

= 200 mV p-p)

04315-0-024

µs/DIV

1V/DIV

50mV/DIV

Figure 8. Rise/Fall Time

04315-0-021

µs/DIV

2V/DIV

100mV/DIV

Figure 9. Differential Overload Recovery (Falling)

AD8205

Rev. 0 | 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 cur-
rent shunt voltages in the presence of rapidly changing common-
mode 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 operat-
ing temperature range for the packaged part. The die input off-
set 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 (ab-
solute 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 common-mode rejection ratio
over the operating temperature is 76 dB for both the die and
packaged part.

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 R

, R

, and

, 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 resis-
tance of R

, R

, and R

is approximately 200 k ± 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 ref-
erence 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 sec-
ond stage is 32.15.

The reference inputs, V

REF

1 and V

REF

2, 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 R

, R

, and R

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

OUT

REF

Figure 13. Simplified Schematic

AD8205

Rev. 0 | 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 cur-
rents 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 = NO CONNECT

GND

V+

OUT

REF

Figure 14. Ground Referenced Output

Table 4. V+ = 5 V

(Referred to -IN)

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 posi-
tive 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 = NO CONNECT

GND

V+

OUT

REF

Figure 15. V+ Referenced Output

Table 5. V+ = 5 V

(Referred to -IN)

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, V

= 2.5 with V

= 0 V

(Referred to -IN)

+40 mV

4.5 V

-40 mV

0.5 V

Adjusting the output is accomplished by applying voltage(s) to
the reference inputs.

REF

1 and V

REF

2 are tied to internal resistors that connect to an

internal offset node. There is no operational difference between
the pins.

AD8205

Rev. 0 | 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 = NO CONNECT

GND

V+

OUT

REF

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 = NO CONNECT

GND

V+

OUT

REF

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 V

REF

pin to

ground and the other V

REF

pin to the reference (see Figure 18).

04315-0-017

AD8205

+IN

IN

NC = NO CONNECT

GND

V+

OUT

REF

VOLTAGE

REFERENCE

Figure 18. Split External Reference

AD8205

Rev. 0 | Page 11 of 12

APPLICATIONS

A typical application for the AD8205 is high-side measurement
of a current through a solenoid for PWM control of the sole-
noid opening. Typical applications include hydraulic transmis-
sion 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

OUT

IN

GND V

REF

2 NC

INDUCTIVE

LOAD

AD8205

CLAMP

DIODE

42V

BATTERY

SHUNT

SWITCH

NC = NO CONNECT

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 pro-
viding 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 connected
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 voltage to be held one
diode drop below ground by the clamp diode.

04315-0-019

+IN V

REF

1 +V

OUT

IN

GND V

REF

2 NC

INDUCTIVE

LOAD

AD8205

CLAMP

DIODE

42V

BATTERY

SHUNT

SWITCH

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 typi-
cally 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 bidirec-
tional mode, see the Output Offset Adjustment section.

04315-0-020

+IN V

REF

1 +V

OUT

IN

GND V

REF

2 NC

AD8205

SHUNT

2.5V

CONTROLLER

NC = NO CONNECT

MOTOR

Figure 21. Motor Control Application

AD8205

Rev. 0 | Page 12 of 12

OUTLINE DIMENSIONS

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)

5.00 (0.1968)
4.80 (0.1890)

4.00 (0.1574)
3.80 (0.1497)

1.27 (0.0500)

BSC

6.20 (0.2440)
5.80 (0.2284)

0.51 (0.0201)
0.31 (0.0122)

COPLANARITY

0.10

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-012AA

Figure 22. 8-Lead Standard Small Outline Package [SOIC]

Narrow Body

(R-8)

Dimensions shown in millimeters and (inches)

ORDERING GUIDE

Models

Temperature Range

Package Description

Package Option

AD8205YR

-40°C to +125°C

8-Lead SOIC

R-8

AD8205YR-REEL

-40°C to +125°C

8-Lead SOIC, 13" Tape and Reel

R-8

AD8205YR-REEL7

-40°C to +125°C

8-Lead SOIC, 7" Tape and Reel

R-8

AD8205YCSURF

-40°C to +150°C

Die Form

regis-

tered trademarks are the property of their respective owners.

D0431504/04(0)

Part Number AD8205

Document Outline