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High Resolution, Zero-Drift Current Shunt Monitor AD8217
FEATURES
High common-mode voltage range 4.5 V to 80 V operating 0 V to 85 V survival Buffered output voltage Wide operating temperature range: -40C to +125C Excellent ac and dc performance 100 nV/C typical offset drift 100 V/C typical offset 5 ppm/C typical gain drift 100 dB typical CMRR at dc
FUNCTIONAL BLOCK DIAGRAM
AD8217
-IN +IN R2 LDO
09161-001
R4
R1 OUT R3
GND
Figure 1.
APPLICATIONS
High side current sensing 48 V telecom Power management Base stations Unidirectional motor control Precision high voltage current sources
GENERAL DESCRIPTION
The AD8217 is a high voltage, high-resolution current shunt amplifier. It features a set gain of 20 V/V, with a maximum 0.35% gain error over the entire temperature range. The buffered output voltage directly interfaces with any typical converter. The AD8217 offers excellent common-mode rejection from 4.5 V to 80 V, and includes an internal LDO, which directly powers the device from the high voltage rail. Therefore, no additional supply is necessary, provided that the input common-mode range is 4.5 V to 80 V. The AD8217 performs unidirectional current measurements across a shunt resistor in a variety of industrial and telecom applications including motor control, battery management, and base station power amplifier bias control. The AD8217 offers breakthrough performance throughout the -40C to +125C temperature range. It features a zero-drift core, which leads to a typical offset drift of 100 nV/C throughout the operating temperature and common-mode voltage range. Special attention is devoted to output linearity being maintained throughout the input differential voltage range of 0 mV to 250 mV, regardless of the common-mode voltage present, and the typical input offset voltage is 100 V. The AD8217 is offered in a 8-lead MSOP package and is specified from -40C to +125C.
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: 781.461.3113 (c)2010 Analog Devices, Inc. All rights reserved.
AD8217 TABLE OF CONTENTS
Features .............................................................................................. 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 ...................................................................... 10 Amplifier Core ............................................................................ 10 Internal LDO............................................................................... 10 Application Notes ........................................................................... 11 Output Linearity ......................................................................... 11 Applications Information .............................................................. 12 High-Side Current Sensing ....................................................... 12 Motor Control Current Sensing ............................................... 12 Outline Dimensions ....................................................................... 13 Ordering Guide .......................................................................... 13
REVISION HISTORY
7/10--Revision 0: Initial Version
Rev. 0 | Page 2 of 16
AD8217 SPECIFICATIONS
TOPR = -40C to +125C, TA = 25C, RL = 25 k, input common-mode voltage (VCM = 4.5 V) (RL is the output load resistor), unless otherwise noted. Table 1.
Parameter GAIN Initial Accuracy Accuracy over Temperature Gain vs. Temperature VOLTAGE OFFSET Offset Voltage (RTI) 1 Over Temperature (RTI)1 Offset Drift INPUT Bias Current 2 Common-Mode Input Voltage Range Differential Input Voltage Range 3 Common-Mode Rejection (CMRR) OUTPUT Output Voltage Range Low Output Voltage Range High Output Impedance DYNAMIC RESPONSE Small Signal -3 dB Bandwidth Slew Rate NOISE 0.1 Hz to 10 Hz, (RTI)1 Spectral Density, 1 kHz, (RTI)1 POWER SUPPLY Operating Range Quiescent Current Over Temperature Power Supply Rejection Ratio (PSRR) TEMPERATURE RANGE For Specified Performance
1 2
Min
Typ 20 0.1
Max
Unit V/V % % ppm/C V V nV/C A A V mV dB V V kHz V/s V p-p nV/Hz
Test Conditions/Comments
0.35 5 250 300 100 500 4.5 90 0.01 5 2 500 1 2.3 110 4.5 90 -40 110 +125 80 800 250 100 800 80
VO 0.1 V dc, TA TOPR TOPR 25C TOPR TOPR TA TOPR Common-mode continuous Differential input voltage TOPR TA 4 TA4
V A dB C
Power regulated from common mode Throughout input common mode TOPR
RTI = referred to input. Refer to Figure 8 for further information on the input bias current. This current varies based on the input common-mode voltage. Additionally, the input bias current flowing to the +IN pin is also the supply current to the internal LDO. 3 The differential input voltage is specified as 250 mV typical because the output is internally clamped to 5 V. This ensures the output voltage does not exceed 5 V and can interface and not cause damage to any typical converter, regardless of the high voltage present at the inputs of the AD8217 (up to 80 V). 4 See Figure 17 and Figure 18 for further information on the output range of the AD8217 with various loads. The AD8217 output clamps to a maximum voltage of 5.6 V when the voltage at pin +IN is greater than 5.6 V. When the voltage at +IN is less than 5.6 V, the output reaches a maximum value of (V+IN - 100 mV).
Rev. 0 | Page 3 of 16
AD8217 ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Maximum Input Voltage ( +IN, -IN to GND) Differential Input Voltage (+IN to -IN) HBM (Human Body Model) ESD Rating Operating Temperature Range (TOPR) Storage Temperature Range Output Short-Circuit Duration Rating 0 V to 85 V 1 V 2000 V -40C to +125C -65C to +150C 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. 0 | Page 4 of 16
AD8217 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
+IN 1 NC 2 NC 3 GND 4
8
-IN NC NC
09161-002
AD8217
TOP VIEW (Not to Scale)
7 6 5
OUT
NC = NO CONNECT
Figure 2. Pin Configuration
Table 3. Pin Function Descriptions
Pin No. 1 2 3 4 5 6 7 8 Mnemonic +IN NC NC GND OUT NC NC -IN Description Noninverting Input. Supply pin to the internal LDO. No Connect. No internal connection to pin. No Connect. No internal connection to pin. Ground. Output. No Connect. No internal connection to pin. No Connect. No internal connection to pin. Inverting Input.
Rev. 0 | Page 5 of 16
AD8217 TYPICAL PERFORMANCE CHARACTERISTICS
40 38 36
30 27 24 21 MAGNITUDE (dB)
34
VOSI (V)
18 15 12 9
32 30 28
6
26 24 -40
3
09161-006
0
-20 0 20 40 60 80 100 120 140 TEMPERATURE (C)
09161-003
1k
10k 100k FREQUENCY (Hz)
1M
Figure 3. Typical Input Offset vs. Temperature
140 130
Figure 6. Typical Small-Signal Bandwidth (VOUT = 200 mV p-p)
10 9 8 7 6 5 4 3 2 1 0 -1 -2 -3 -4 -5
110 CMRR (dB) 100 90 80 70 60 50 100 -40C +25C +125C
TOTAL OUTPUT ERROR (%)
120
1000
10k FREQUENCY (Hz)
100k
1M
Figure 4. Typical CMRR vs. Frequency
500 450
INPUT BIAS CURRENT (A)
09161-004
0
5
10
15 20 25 30 35 DIFFERENTIAL INPUT (mV)
40
45
50
Figure 7. Total Output Error vs. Differential Input Voltage
800 700 600 500 400 300 200 100
-IN
09161-005
+IN
400
GAIN ERROR (ppm)
350 300 250 200 150 100 -40
-20
0
20 40 60 TEMPERATURE (C)
80
100
120
0
5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 INPUT COMMON-MODE VOLTAGE (V)
Figure 5. Typical Gain Error vs. Temperature
Figure 8. Input Bias Current vs. Input Common-Mode Voltage (Differential Input Voltage = 5 mV)
Rev. 0 | Page 6 of 16
09161-008
0
09161-007
AD8217
INPUT INPUT 5mV/DIV 100mV/DIV
OUTPUT 2V/DIV OUTPUT 100mV/DIV 1s/DIV
09161-009
5s/DIV
Figure 9. Rise Time (Differential Input = 5 mV)
Figure 12. Fall Time (Differential Input = 200 mV)
INPUT INPUT 100mV/DIV 200mV/DIV
OUTPUT
09161-010
OUTPUT
09161-013 09161-014
2V/DIV 5s/DIV
2V/DIV 5s/DIV
Figure 10. Rise Time (Differential Input = 200 mV)
Figure 13. Differential Overload Recovery, Rising
INPUT 5mV/DIV
INPUT 200mV/DIV
OUTPUT 100mV/DIV
OUTPUT 2V/DIV
09161-011
1s/DIV
5s/DIV
Figure 11. Fall Time (Differential Input = 5 mV)
Figure 14. Differential Overload Recovery, Falling
Rev. 0 | Page 7 of 16
09161-012
AD8217
12.0 11.0 10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5
09161-015
250
OUTPUT VOLTAGE RANGE FROM GND (V)
MAXIMUM OUTPUT SINK CURRENT (mA)
11.5
200
150
100
50
0 10 20 30 40 50 60 70 80 90 100 110 120 TEMPERATURE (C)
0
0.5
1.0
1.5 2.0 2.5 3.0 3.5 OUTPUT SINK CURRENT (mA)
4.0
4.5
5.0
Figure 15. Maximum Output Sink Current vs. Temperature
9.5
Figure 18. Output Voltage Range From GND vs. Output Sink Current
MAXIMUM OUTPUT SOURCE CURRENT (mA)
9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0
09161-019
INPUT 50V/DIV
OUTPUT 1V/DIV
4.5 4.0
0
-40
-30
-20
-10
100
110
10
20
30
40
50
60
70
80
90
120
130
140
150
TEMPERATURE (C)
09161-016
500ns/DIV
Figure 16. Maximum Output Source Current vs. Temperature
5.010
Figure 19. Common-Mode Step Response, Rising
OUTPUT VOLTAGE SWING FROM RAIL (V)
5.000 4.990 4.980 4.970 4.960 4.950 4.940 4.930 4.920
09161-020
INPUT 50V/DIV OUTPUT 1V/DIV
4.910 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 OUTPUT SOURCE CURRENT (mA) 4.5 5.0
09161-017
4.900
1s/DIV
Figure 17. Output Voltage Range vs. Output Source Current
Figure 20. Common-Mode Step Response (Falling)
Rev. 0 | Page 8 of 16
09161-018
5.0 -40 -30 -20 -10
0
AD8217
800
1200
700 600 500
COUNT
09161-021
1000
COUNT
800
400 300
600
400
200
200
09161-023
100 0
0 -200
-150
-100
-50
0 VOSI (V)
50
100
150
200
-0.4
-0.2
0 OFFSET DRIFT (V/C)
0.2
0.4
Figure 21. Input Offset Distribution
Figure 23. Input Offset Drift Distribution
1000
800
COUNT
600
400
200
09161-022
0 -10
-5
0 GAIN DRIFT (ppm/C)
5
10
Figure 22. Gain Drift Distribution
Rev. 0 | Page 9 of 16
AD8217 THEORY OF OPERATION
AMPLIFIER CORE
In typical applications, the AD8217 amplifies a small differential input voltage generated by the load current flowing through a shunt resistor. The AD8217 rejects high common-mode voltages (up to 80 V) and provides a ground-referenced, buffered output that interfaces with an analog-to-digital converter (ADC). Figure 24 shows a simplified schematic of the AD8217.
AD8217
ILOAD -IN V2 LOAD V1 4.5V TO 80V SHUNT +IN R2 LDO
09161-024
The AD8217 accurately amplifies the input differential signal, rejecting high voltage common modes ranging from 4.5 V to 80 V. The main amplifier uses a novel zero-drift architecture, providing the end user with an extremely stable part over temperature. The offset drift is typically less than 100 nV/C. This performance leads to optimal accuracy and dynamic range.
INTERNAL LDO
The AD8217 includes an internal LDO, which allows the device to power directly from the common-mode voltage at the inputs. No additional standalone supply is necessary, provided that the common-mode voltage at the +IN pin is at least 4.5 V and up to 80 V. Once the common-mode voltage is above 5.6 V, the LDO output reaches its maximum value, that is 5.6 V. This is also the maximum output voltage range of the AD8217. Because the AD8217 output typically interfaces with a converter, the 5.6 V maximum output range ensures the ADC input is not damaged due to excessive overvoltage. The input bias current flowing through Pin +IN powers the internal LDO and, therefore, doubles as the supply current for the AD8217. This current varies depending on the input common-mode voltage. See Figure 8 for additional information.
R4
R1 OUT R3
GND
Figure 24. Simplified Schematic
The AD8217 is configured as a difference amplifier. The transfer function is OUT = (R4/R1) x (V1 - V2) Resistors R4 and R1 are matched to within 0.01% and have values of 1.5 M and 75 k, respectively, meaning an input to output total gain of 20 V/V for the AD8217.
Rev. 0 | Page 10 of 16
AD8217 APPLICATION NOTES
OUTPUT LINEARITY
In all current sensing applications where the common-mode voltage can vary significantly, it is important that the current sensor maintain the specified output linearity, regardless of the input differential or common-mode voltage. The AD8217 maintains a very high input-to-output linearity even when the differential input voltage is very small.
200 180 160 140
Regardless of the common mode, the AD8217 provides a correct output voltage when the input differential is at least 1 mV. The ability of the AD8217 to work with very small differential inputs, regardless of the common-mode voltage, allows for optimal dynamic range, accuracy, and flexibility in any current sensing application.
OUTPUT (mV)
120 100 80 60 40 20
09161-025
0
0 1 2 3 4 5 6 7 DIFFERENTIAL INPUT (mV) 8 9 10
Figure 25. Gain Linearity at Small Differential Inputs (VCM = 4.5 V to 80 V)
Rev. 0 | Page 11 of 16
AD8217 APPLICATIONS INFORMATION
HIGH-SIDE CURRENT SENSING
In this configuration, the shunt resistor is referenced to the battery (see Figure 26). High voltage is present at the inputs of the current sense amplifier. When the shunt is battery referenced, the AD8217 produces a linear ground-referenced analog output. The AD8217 includes an internal LDO, which allows the part to be powered from the high voltage rail, with no need for an additional standalone supply.
ILOAD 4.5V TO 80V SHUNT +IN -IN
MOTOR CONTROL CURRENT SENSING
The AD8217 is a practical, accurate 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 27), the AD8217 monitors the current with no additional supply pin necessary.
BATTERY IMOTOR
ADC
+IN
-IN
MOTOR
AD8217
GND
09161-026
AD8217
OUT
09161-027
OUT
GND
Figure 26. Battery-Referenced Shunt Resistor
Figure 27. High-Side Current Sensing in Motor Control
Rev. 0 | Page 12 of 16
AD8217 OUTLINE DIMENSIONS
3.20 3.00 2.80
8
5
3.20 3.00 2.80 PIN 1 IDENTIFIER
1
5.15 4.90 4.65
4
0.65 BSC 0.95 0.85 0.75 0.15 0.05 COPLANARITY 0.10 0.40 0.25 15 MAX 1.10 MAX 0.80 0.55 0.40
100709-B
6 0
0.23 0.09
COMPLIANT TO JEDEC STANDARDS MO-187-AA
Figure 28. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters
ORDERING GUIDE
Model 1 AD8217BRMZ AD8217BRMZ-RL AD8217BRMZ-R7
1
Temperature Range -40C to +125C -40C to +125C -40C to +125C
Package Description 8-Lead Mini Small Outline Package (MSOP) 8-Lead Mini Small Outline Package (MSOP) 8-Lead Mini Small Outline Package (MSOP)
Package Option RM-8 RM-8 RM-8
Branding Y2L Y2L Y2L
Z = RoHS Compliant Part.
Rev. 0 | Page 13 of 16
AD8217 NOTES
Rev. 0 | Page 14 of 16
AD8217 NOTES
Rev. 0 | Page 15 of 16
AD8217 NOTES
(c)2010 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D09161-0-6/10(0)
Rev. 0 | Page 16 of 16

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