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Single-Supply 42 V System Difference Amplifier AD8205
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: -40C to +150C 8-lead SOIC: -40C to +125C Adjustable offset Available in SOIC and die form
FUNCTIONAL BLOCK DIAGRAM
V+
6
+IN 8
5
OUT
-IN 1
AD8205
7
VREF1
3
NC 4
2
VREF2
04315-0-001
EXCELLENT AC AND DC PERFORMANCE
15 V/C offset drift 30 ppm/C gain drift 80 dB CMRR dc to 20 kHz
NC = NO CONNECT
GND
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 25C higher (up to 150C) 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 V/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 (c) 2004 Analog Devices, Inc. All rights reserved.
AD8205 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
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 Conditions AD8205 SOIC Min Typ Max 50 VO 0.1 V dc, 25C Specified Temperature Range 30 25C Specified Temperature Range 15 2 4.5 15 1 1.2 30 2.5 6 Min AD8205 DIE Typ Max 50 1 1.3 Unit V/V % % ppm/C mV mV V/C
400 200 Common Mode, Continuous Differential1 25C, f = DC to 20 kHz2 Operating Temperature Range, f = DC to 20 kHz2 RL = 25 k -2 78 76 100 86 80 65 -2 78 76
400 200 65 100 86 80
k k V mV dB dB
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
0.05 200 50 0.5 20 0.5
4.8
0.05 200 50 0.5 20 0.5
4.8
V kHz V/s V p-p V/Hz
Divider to Supplies Voltage applied to VREF1 and VREF2 in Parallel VS = 5 V
0.497
0.503 2 4.8 40 5.5 2
0.497
0.503 2 4.8 40 5.5 2
V/V mV/V V k V mA dB C
0.05 24 4.5
32
0.05 24 4.5 70
32
VO = 0.1 V dc 70 Operating Temperature Range -40
+125
-40C
+150
1 2
Input voltage range = 50 mV with half-scale offset. Source imbalance < 2 . 3 The offset adjustment is ratiometric to the power supply when VREF1 and VREF2 are used as a divider between the supplies.
Rev. 0 | Page 3 of 12
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 -40C to +125C -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 GND 2 VREF2 3
8
+IN
NC = NO CONNECT
Figure 3. Pin Configuration
Table 3. Pin Function Descriptions
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
Figure 2. Metallization Diagram
04315-0-002
Die size is 1170 m by 1280 m. Die thickness is 13 mil. Minimum passivation opening (minimum bond pad size) is 92 m x 92 m. 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
04315-0-026
VREF1 TOP VIEW 6 V+ (Not to Scale) NC 4 5 OUT
7
AD8205
AD8205 TYPICAL PERFORMANCE CHARACTERISTICS
500 400 300 30 200
VOSI (V)
40 35
TYP. VOSI (DIE)
0 -100 -200 -300
04315-0-003
GAIN (dB)
100
25 20 15 10
TYP. VOSI (SOIC)
-400 -500 -40 -20 0 20 40 60 80 TEMPERATURE (C) 100 120 140
5 0 10
100
1k 10k FREQUENCY (Hz)
100k
1M
Figure 4. Typical Offset Drift
120 110 100 90 80
CMR (dB)
Figure 7. Typical Small Signal Bandwidth (VOUT = 200 mV p-p)
50mV/DIV
70 60 50 40 30
04315-0-005
04315-0-024
20 10 0 10 100 1k 10k 100k FREQUENCY (Hz) 1M
1V/DIV
10M
40s/DIV
Figure 5. CMR vs. Frequency
12000 10000 8000 6000
GAIN ERROR (ppm)
100mV/DIV
Figure 8. Rise/Fall Time
4000 2000 0 -2000 -4000 -6000 -8000 TYP. DIE
04315-0-021
TYP. IN SOIC
2V/DIV
-10000 -12000 -40 -20 0 20 40 60 80 TEMPERATURE (C) 100 120 140
04315-0-007
2s/DIV
Figure 6. Gain Drift
Figure 9. Differential Overload Recovery (Falling)
Rev. 0 | Page 6 of 12
04315-0-008
AD8205
50V/DIV
100mV/DIV
50mV/DIV
04315-0-022
2s/DIV
1s/DIV
Figure 10. Differential Overload Recovery (Rising)
Figure 12. Common-Mode Response
2V/DIV
0.01%/DIV
40s/DIV
Figure 11. Settling Time
04315-0-025
Rev. 0 | Page 7 of 12
04315-0-023
2V/DIV
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 -40C to +125C. The die temperature range is -40C to +150C with a guaranteed gain accuracy of 1.3%. The input offset is less than 2 mV referred to the input at 25C, 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. 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 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 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 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 A current sink pull-down.
-IN RA +IN RA A1 RB RB RF RF RD RD
RC
RC
A2 RE RF
VOUT VREF1 RREF RREF
04315-0-012
250mV
AD8205
GND
VREF2
Figure 13. Simplified Schematic
Rev. 0 | Page 8 of 12
AD8205 OUTPUT OFFSET ADJUSTMENT
The output of the AD8205 can be adjusted for unidirectional or bidirectional operation.
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).
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.
V+ +IN OUT -IN
AD8205
VREF1
NC GND NC = NO CONNECT
VREF2
04315-0-014
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
Figure 15. V+ Referenced Output
VIN (Referred to -IN) 0V 100 mV
VO 4.8 V 0.05 V
V+ +IN OUT -IN
BIDIRECTIONAL OPERATION
Bidirectional operation allows the AD8205 to measure currents through a resistive shunt in two directions.
AD8205
VREF1
NC GND NC = NO CONNECT
VREF2
04315-0-013
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) +40 mV -40 mV VO 4.5 V 0.5 V
Figure 14. Ground Referenced Output
Table 4. V+ = 5 V
VIN (Referred to -IN) 0V 100 mV VO 0.05 V 4.8 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
AD8205
V+ +IN OUT -IN
VREF1
NC GND
VREF2
04315-0-016
AD8205
VREF1
NC = NO CONNECT
2.5V VOLTAGE REFERENCE
Figure 17. Split Supply
NC GND NC = NO CONNECT VREF2
04315-0-015
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).
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.
+IN -IN
V+ OUT
AD8205
VREF1
5V
VOLTAGE REFERENCE
NC GND NC = NO CONNECT
VREF2
04315-0-017
Figure 18. Split External Reference
Rev. 0 | Page 10 of 12
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
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 INDUCTIVE LOAD
42V BATTERY
SWITCH +IN VREF1 +VS SHUNT -IN CLAMP DIODE OUT
AD8205
GND VREF2 NC
NC = NO CONNECT
Figure 20. High-Side Switch
CLAMP DIODE 42V BATTERY SHUNT
+IN VREF1 +VS
OUT
AD8205
-IN GND VREF2 NC
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.
5V CONTROLLER
SWITCH
04315-0-018
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 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.
MOTOR
+IN VREF1 +VS SHUNT -IN
OUT
AD8205
GND VREF2 NC 5V
04315-0-020
2.5V NC = NO CONNECT
Figure 21. Motor Control Application
Rev. 0 | Page 11 of 12
04315-0-019
INDUCTIVE LOAD
AD8205 OUTLINE DIMENSIONS
5.00 (0.1968) 4.80 (0.1890)
8 5
4.00 (0.1574) 3.80 (0.1497) 1
6.20 (0.2440)
4 5.80 (0.2284)
1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040)
1.75 (0.0688) 1.35 (0.0532)
0.50 (0.0196) x 45 0.25 (0.0099)
0.51 (0.0201) COPLANARITY SEATING 0.31 (0.0122) 0.10 PLANE
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 -40C to +125C -40C to +125C -40C to +125C -40C to +150C Package Description 8-Lead SOIC 8-Lead SOIC, 13" Tape and Reel 8-Lead SOIC, 7" Tape and Reel Die Form Package Option R-8 R-8 R-8
(c) 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

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