Zero Drift, Bidirectional Current Shunt Monitor AD8218 Data Sheet FUNCTIONAL BLOCK DIAGRAM High common-mode voltage range 4 V to 80 V operating -0.3 V to +85 V survival Buffered output voltage Gain = 20 V/V Wide operating temperature range: -40C to +125C Excellent ac and dc performance 100 nV/C typical offset drift 50 V typical offset 5 ppm/C typical gain drift 110 dB typical CMRR at dc VS R4 AD8218 -IN R1 OUT +IN R2 LDO R3 ENB GND REF 09592-001 FEATURES Figure 1. APPLICATIONS High-side current sensing 48 V telecom Power management Base stations Bidirectional motor control Precision high voltage current sources GENERAL DESCRIPTION The AD8218 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 AD8218 offers excellent input common-mode rejection from 4 V to 80 V. The AD8218 performs bidirectional 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 AD8218 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 range and the 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. The AD8218 also includes an internal 80 mV reference that can be enabled for optimal dynamic range in unidirectional current sense applications. The typical input offset voltage is 50 V. The AD8218 is offered in an 8-lead MSOP package and an 8-lead LFCSP package. Rev. B Document Feedback 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 (c)2011-2013 Analog Devices, Inc. All rights reserved. Technical Support www.analog.com AD8218 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Output Clamping ....................................................................... 10 Applications ....................................................................................... 1 Application Notes ........................................................................... 11 Functional Block Diagram .............................................................. 1 Supply (VS) Connections ........................................................... 11 General Description ......................................................................... 1 Enable Pin (ENB) Operation .................................................... 11 Revision History ............................................................................... 2 Applications Information .............................................................. 12 Specifications..................................................................................... 3 Unidirectional High-Side Current Sensing ............................ 12 Absolute Maximum Ratings............................................................ 4 Bidirectional High-Side Current Sensing ............................... 12 ESD Caution .................................................................................. 4 Motor Control Current Sensing ............................................... 12 Pin Configurations and Function Descriptions ........................... 5 Outline Dimensions ....................................................................... 13 Typical Performance Characteristics ............................................. 6 Ordering Guide .......................................................................... 13 Theory of Operation ...................................................................... 10 Amplifier Core ............................................................................ 10 REVISION HISTORY 4/13--Rev. A to Rev. B Added 8-Lead LFCSP ......................................................... Universal Changes to General Description Section ...................................... 1 Added Figure 3, Renumbered Sequentially .................................. 5 Changes to Table 3 ............................................................................ 5 Added Figure 37.............................................................................. 13 Updated Outline Dimensions ....................................................... 13 Changes to Ordering Guide .......................................................... 13 2/11--Rev. 0 to Rev. A Changes to Features.......................................................................... 1 1/11--Revision 0: Initial Version Rev. B | Page 2 of 16 Data Sheet AD8218 SPECIFICATIONS TOPR = -40C to +125C, TA = 25C, RL = 25 k (RL is the output load resistor), input common-mode voltage (VCM) = 4 V, unless otherwise noted. Table 1. Parameter GAIN Initial Accuracy Accuracy over Temperature Gain vs. Temperature VOLTAGE OFFSET Offset Voltage (RTI 1) Over Temperature (RTI1) 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 INTERNAL REFERENCE (ENB PIN CONNECTED TO GND) Initial Value Offset (RTI1) Offset Drift (RTO 4) REFERENCE INPUT (REF, PIN 7) Input Impedance Input Current Input Voltage Range Input-to-Output Gain DYNAMIC RESPONSE Small-Signal -3 dB Bandwidth Slew Rate NOISE 0.1 Hz to 10 Hz (RTI1) Spectral Density, 1 kHz (RTI1) POWER SUPPLY Operating Range (Pin 2 Floating) VS Range (Pin 2) Quiescent Current over Temperature Power Supply Rejection Ratio (PSRR) TEMPERATURE RANGE For Specified Performance Min Typ Max Unit Test Conditions/Comments V/V % % ppm/C VO 0.1 V dc, TA TOPR TOPR V V nV/C 25C TOPR TOPR 220 80 250 A A V mV dB TA, input common mode = 4 V, VS = 4 V TOPR, input common mode = 4 V, VS = 4 V Common-mode continuous Differential input voltage TOPR VS - 0.1 TA 2 V V 80 mV Voltage at OUT with a differential input of 0 V and a common-mode input of 4 V 20 0.1 0.35 5 200 300 100 130 4 0 90 110 0.01 -150 +150 10 1.5 V V/C 1 0.0001 M A V V/V 450 1 kHz V/s 2.3 110 V p-p nV/Hz 3 0 60 5 VS = NC or VS = 5 V Dependent on VREF/1.5 M ENB not connected to GND 4 80 V Power regulated from common mode, VS pin floating 4 5.5 V VS must be less than 5.5 V if standalone supply is used 800 A dB Throughout input common mode TOPR +125 C 90 110 -40 RTI = referred to input. Refer to Figure 9 for more information on the input bias current. This current varies based on the input common-mode voltage. 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 because the output is internally clamped to 5.2 V. This ensures that the output voltage does not exceed the typical ADC input range, preventing damage. The AD8218 can survive up to 5 V differentially but will only amplify ~250 mV correctly due to the output clamping function. 4 RTO = referred to output. 1 2 Rev. B | Page 3 of 16 AD8218 Data Sheet ABSOLUTE MAXIMUM RATINGS Table 2. Parameter Maximum Input Voltage ( +IN, -IN to GND) Differential Input Voltage (+IN to -IN) Human Body Model (HBM) ESD Rating Operating Temperature Range (TOPR) Storage Temperature Range Output Short-Circuit Duration Rating -0.3 V to +85 V 5 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. B | Page 4 of 16 Data Sheet AD8218 PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS ENB 3 AD8218 TOP VIEW (Not to Scale) GND 4 8 -IN +IN 1 7 REF VS 2 6 NC 5 OUT NC = NO CONNECT. DO NOT CONNECT TO THIS PIN. ENB 3 GND 4 8 -IN AD8218 TOP VIEW (Not to Scale) 7 REF 6 NC 5 OUT NOTES 1. NC = NO CONNECT. DO NOT CONNECT TO THIS PIN. 2. THE EXPOSED PAD NEEDS TO BE CONNECTED TO PIN 4 (GND). Figure 2. MSOP Pin Configuration Figure 3. LFCSP Pin Configuration Table 3. Pin Function Descriptions Pin No. 1 2 3 4 5 6 7 8 Mnemonic +IN VS ENB GND OUT NC REF -IN EPAD Description Noninverting Input. Supply Pin. Bypass with a standard 0.1 F capacitor. Enable. Connect to GND to enable the internal 80 mV reference. Ground. Output. No Connect. Do not connect to this pin. Reference Input. Connect to a low impedance voltage. Inverting Input. Exposed Pad. The exposed pad needs to be connected to Pin 4 (GND). Applies to LFCSP only. Rev. B | Page 5 of 16 09592-103 VS 2 09592-002 +IN 1 AD8218 Data Sheet TYPICAL PERFORMANCE CHARACTERISTICS 30 40 27 38 24 36 MAGNITUDE (dB) 21 VOSI (V) 34 32 30 18 15 12 9 28 6 26 0 20 40 60 80 100 120 140 TEMPERATURE (C) 0 1k Figure 4. Typical Input Offset vs. Temperature 10k 100k FREQUENCY (Hz) 1M 09592-006 -20 09592-003 24 -40 3 Figure 7. Typical Small-Signal Bandwidth (VOUT = 200 mV p-p) 10 140 9 130 8 TOTAL OUTPUT ERROR (%) 120 CMRR (dB) 110 100 90 -40C +25C +125C 80 70 7 6 5 4 3 2 1 0 -1 -2 -3 60 10k 1M 100k FREQUENCY (Hz) -5 09592-004 1000 0 Figure 5. Typical CMRR vs. Frequency 450 700 INPUT BIAS CURRENT (A) 800 400 350 300 250 200 15 20 25 30 35 DIFFERENTIAL INPUT (mV) 40 45 50 +IN 600 500 400 300 200 100 150 -20 0 60 40 20 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 6. Typical Gain Error vs. Temperature Figure 9. Input Bias Current vs. Input Common-Mode Voltage (Differential Input Voltage = 5 mV, VS = NC) Rev. B | Page 6 of 16 09592-008 -IN 0 09592-005 GAIN ERROR (ppm) 10 Figure 8. Total Output Error vs. Differential Input Voltage 500 100 -40 5 09592-007 -4 50 100 Data Sheet AD8218 500 INPUT 5mV/DIV 400 OUTPUT 350 100mV/DIV 300 0 20 40 60 80 100 120 TEMPERATURE (C) 1s/DIV Figure 10. Supply Current vs. Temperature (VS = 5 V, VCM = 12 V) 09592-011 -20 Figure 13. Fall Time (Differential Input = 10 mV) INPUT 100mV/DIV INPUT 5mV/DIV OUTPUT 2V/DIV 1s/DIV 5s/DIV Figure 11. Rise Time (Differential Input = 10 mV) 09592-012 100mV/DIV 09592-009 OUTPUT Figure 14. Fall Time (Differential Input = 200 mV) INPUT 200mV/DIV INPUT 100mV/DIV OUTPUT OUTPUT 2V/DIV 2V/DIV 5s/DIV 5s/DIV Figure 12. Rise Time (Differential Input = 200 mV) Figure 15. Differential Overload Recovery, Rising Rev. B | Page 7 of 16 09592-013 200 -40 09592-109 250 09592-010 SUPPLY CURRENT (A) 450 AD8218 Data Sheet 9.5 MAXIMUM OUTPUT SOURCE CURRENT (mA) INPUT 200mV/DIV OUTPUT 09592-014 2V/DIV 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 150 TEMPERATURE (C) Figure 19. Maximum Output Source Current vs. Temperature Figure 16. Differential Overload Recovery, Falling 5.010 81.0 80.5 80.0 79.5 0 80 40 60 20 TEMPERATURE (C) 100 120 4.970 4.960 4.950 4.940 4.930 4.920 4.910 0.5 1.0 1.5 2.0 2.5 3.0 4.0 3.5 4.5 5.0 OUTPUT SOURCE CURRENT (mA) Figure 20. Output Voltage Swing from Rail vs. Output Source Current 12.0 250 OUTPUT VOLTAGE RANGE FROM GND (V) 11.5 11.0 10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 0 10 20 30 40 50 60 70 80 90 100 110 120 TEMPERATURE (C) 200 150 100 50 0 09592-015 MAXIMUM OUTPUT SINK CURRENT (mA) 4.980 0 Figure 17. Internal Reference Voltage vs. Temperature (VS = 5 V, VS = NC, VCM = 12 V, Pin 1 (+IN) and Pin 8 (-IN) Shorted, Pin 3 (ENB) Shorted to Pin 4 (GND)) 5.0 -40 -30 -20 -10 4.990 4.900 09592-116 -20 5.000 0 Figure 18. Maximum Output Sink Current vs. Temperature 0.5 1.0 2.5 3.5 1.5 2.0 3.0 OUTPUT SINK CURRENT (mA) 4.0 4.5 5.0 09592-018 REFERENCE RTO (mV) 81.5 09592-017 OUTPUT VOLTAGE SWING FROM RAIL (V) 82.0 79.0 -40 09592-016 140 130 110 120 100 80 90 60 70 50 40 20 30 0 10 -10 -20 -40 4.0 -30 5s/DIV 9.0 Figure 21. Output Voltage Range from GND vs. Output Sink Current Rev. B | Page 8 of 16 Data Sheet AD8218 500 INPUT 400 COUNT 50V/DIV OUTPUT 300 200 1V/DIV 500ns/DIV 0 -4 09592-022 09592-019 100 -3 -2 -1 0 1 2 3 4 GAIN DRIFT (ppm/C) Figure 22. Common-Mode Step Response, Rising Figure 25. Gain Drift Distribution 140 120 INPUT 50V/DIV COUNT 100 OUTPUT 1V/DIV 80 60 40 1s/DIV 0 -0.6 09592-023 09592-020 20 -0.2 -0.4 0 0.4 0.2 0.6 OFFSET DRIFT (V/C) Figure 26. Input Offset Drift Distribution Figure 23. Common-Mode Step Response, Falling 180 250 150 200 COUNT 90 150 100 60 0 -200 -100 0 100 09592-024 50 30 09592-021 COUNT 120 0 -5 200 0 5 10 INTERNAL REF OFFSET DRIFT (V/C) VOSI (V) Figure 24. Input Offset Distribution Figure 27. Internal REF Offset Drift Distribution, Referred to Output (RTO) Rev. B | Page 9 of 16 15 AD8218 Data Sheet THEORY OF OPERATION The AD8218 is configured as a difference amplifier. The transfer function is AMPLIFIER CORE In typical applications, the AD8218 amplifies a small differential input voltage generated by the load current flowing through a shunt resistor. The AD8218 rejects high common-mode voltages (up to 80 V) and provides a ground-referenced, buffered output. Figure 28 shows a simplified schematic of the AD8218. 5V ILOAD VS ICHARGE Resistors R4 and R1 are matched to within 0.01% and have values of 1.5 M and 75 k, respectively, meaning an inputto-output total gain of 20 V/V for the AD8218. The difference between V1 and V2 is the voltage across the shunt resistor, or VIN. Therefore, the input-to-output transfer function of the AD8218 is CF GND OUT (V) = (20 x VIN) + VREF R4 AD8218 -IN OUT = ((R4/R1) x (V1 - V2)) + VREF The AD8218 accurately amplifies the input differential signal, rejecting high voltage common modes ranging from 4 V to 80 V. R1 V2 OUT SHUNT +IN V1 4V TO 80V R2 LDO The main amplifier uses a novel zero-drift architecture, providing the end user with breakthrough temperature stability. The offset drift is typically less than 100 nV/C. This performance leads to optimal accuracy and dynamic range. R3 ENB REF GND VREF Figure 28. Simplified Schematic 09592-027 LOAD OUTPUT CLAMPING After the input common-mode voltage in the application is above 5.2 V, the internal LDO output of the AD8218 also reaches its maximum value of 5.2 V, which is the maximum output range of the AD8218. Because in typical applications the output interfaces with a converter, clamping the AD8218 output voltage to 5.2 V ensures that the ADC input is not damaged due to excessive overvoltage. Rev. B | Page 10 of 16 Data Sheet AD8218 APPLICATION NOTES SUPPLY (VS) CONNECTIONS ENABLE PIN (ENB) OPERATION The AD8218 includes an internal LDO, which allows the user to leave the VS pin floating, powering the AD8218 directly from the voltage present at Pin 1 (+IN), provided this voltage is in the 4 V to 80 V range. A typical connection for the part in this configuration is shown in Figure 29. The AD8218 includes an internal reference that can be enabled by connecting Pin 3 (ENB) to ground. This mode of operation is shown in Figure 31. ILOAD ICHARGE 4V TO 80V SHUNT BATTERY LOAD +IN -IN VS REF AD8218 VS REF OUT GND 09592-028 Figure 31. Enabling the Internal 80 mV Reference The AD8218 can also be powered from a separate low impedance supply at Pin 2 (VS); however, this voltage can only be in the 4 V to 5.5 V range. In cases where the high voltage bus is susceptible to noise, transients, or high voltage fluctuations and a 5 V supply is available, the AD8218 can be used in the mode depicted in Figure 30. ICHARGE ILOAD 5V -IN ENB 2.5V Figure 29. Operation with No VS Connection SHUNT LOAD +IN -IN VS REF AD8218 OUT (V) = OUT (V) = (20 x VIN) + 0.08 V If Pin 3 is connected to ground, and therefore the internal reference is enabled, 80 mV must always be added to the transfer function of the AD8218. 2.5V OUT ENB In this configuration, the internal 80 mV reference is activated, and the output of the AD8218 is 80 mV when the differential input voltage is 0 V and the voltage at Pin 7 (REF) is also 0 V. This internal reference is useful in unidirectional current measurements where the current being monitored has a very wide range. Setting the output starting point to 80 mV means that when the load current through the shunt resistor is 0 A, the output is 80 mV. This ensures that the output errors due to initial offset and the output saturation range of the amplifier are overcome. In this mode, the transfer function of the AD8218 becomes GND 09592-029 CF LOAD +IN AD8218 GND 4V TO 80V SHUNT OUT ENB BATTERY 4V TO 80V 09592-030 BATTERY ILOAD Figure 30. 5 V Supply Operation Rev. B | Page 11 of 16 AD8218 Data Sheet APPLICATIONS INFORMATION UNIDIRECTIONAL HIGH-SIDE CURRENT SENSING VS ILOAD In the unidirectional high-side current sensing configuration, the shunt resistor is referenced to the battery (see Figure 32). High voltage is present at the inputs of the current sense amplifier. When the shunt is battery referenced, the AD8218 produces a linear ground-referenced analog output. The supply pin, VS, of the AD8218 can either be connected to a 5 V supply or left floating (see the Supply (VS) Connections section). AD8218 R1 -IN V2 OUT SHUNT +IN LOAD V1 R2 BATTERY (4V TO 80V) ENB 09592-033 Figure 34. Bidirectional Operation Using a 2.5 V Reference Input R1 V2 OUT SHUNT +IN LOAD V1 R2 BATTERY (4V TO 80V) ENB GND 2.5V R4 AD8218 -IN R3 LDO REF VS ILOAD R4 LDO R3 The output transfer function curve for bidirectional operation using a 2.5 V reference input is shown in Figure 35. 5.0 4.5 Figure 32. Unidirectional Operation with ENB Connected to GND The output transfer function curve for unidirectional operation with ENB connected to GND is shown in Figure 33. 3.5 3.0 2.5 2.0 1.5 280 1.0 240 0.5 0 -0.15 200 -0.10 0 -0.05 0.05 0.10 0.15 INPUT VOLTAGE (V) 160 Figure 35. Transfer Function When Using a 2.5 V Reference Input 120 MOTOR CONTROL CURRENT SENSING 80 The AD8218 is a practical, accurate solution for high-side current sensing in motor control applications. In cases where the shunt resistor is referenced to a battery and the current flowing is bidirectional (as shown in Figure 36), the AD8218 monitors the current with no additional supply pin necessary. 0 0 1 2 3 4 5 6 7 8 9 10 INPUT VOLTAGE (mV) 09592-032 40 Figure 33. Output Transfer Function with ENB Connected to GND BATTERY BIDIRECTIONAL HIGH-SIDE CURRENT SENSING IMOTOR Inputting a voltage at Pin 7 (REF) offsets the output of the AD8218 and allows for bidirectional current sensing. The transfer function from the REF pin to the output is 1 V/V. For example, a 2.5 V REF input offsets the output of the AD8218 to 2.5 V. See Figure 34 for typical connections. The user must ensure that the voltage applied at Pin 7 (REF) is from a low impedance source. +IN -IN VS REF AD8218 MOTOR VREF OUT ENB GND 09592-035 OUTPUT VOLTAGE (mV) 320 4.0 09592-034 09592-031 GND OUTPUT VOLTAGE (V) REF Figure 36. High-Side Current Sensing in Motor Control Rev. B | Page 12 of 16 Data Sheet AD8218 OUTLINE DIMENSIONS 1.75 1.65 1.50 2.00 BSC 5 3.00 BSC 8 1.90 1.80 1.65 EXPOSED PAD 0.20 MIN 0.50 0.40 0.30 TOP VIEW 0.80 0.75 0.70 COPLANARITY 0.08 0.05 MAX 0.02 NOM 0.30 0.25 0.20 0.50 FOR PROPER CONNECTION OF THE EXPOSED PAD, REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SECTION OF THIS DATA SHEET. 081806-A SEATING PLANE BOTTOM VIEW 0.15 REF SIDE VIEW PIN 1 INDICATOR 1 4 INDEX AREA Figure 37. 8-Lead Lead Frame Chip Scale Package [LFCSP_WD] 2 mm x 3 mm Body, Very Very Thin, Dual Lead (CP-8-4) Dimensions shown in millimeters 3.20 3.00 2.80 8 3.20 3.00 2.80 1 5.15 4.90 4.65 5 4 PIN 1 IDENTIFIER 0.65 BSC 0.95 0.85 0.75 15 MAX 1.10 MAX 0.40 0.25 6 0 0.23 0.09 0.80 0.55 0.40 COMPLIANT TO JEDEC STANDARDS MO-187-AA 10-07-2009-B 0.15 0.05 COPLANARITY 0.10 Figure 38. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters ORDERING GUIDE Model 1 AD8218BCPZ-RL AD8218BCPZ-WP AD8218BRMZ AD8218BRMZ-RL 1 Temperature Range -40C to +125C -40C to +125C -40C to +125C -40C to +125C Package Description 8-Lead Lead Frame Chip Scale Package [LFCSP_WD] 8-Lead Lead Frame Chip Scale Package [LFCSP_WD] 8-Lead Mini Small Outline Package [MSOP] 8-Lead Mini Small Outline Package [MSOP] Z = RoHS Compliant Part. Rev. B | Page 13 of 16 Package Option CP-8-4 CP-8-4 RM-8 RM-8 Branding Y5A Y5A Y3K Y3K AD8218 Data Sheet NOTES Rev. B | Page 14 of 16 Data Sheet AD8218 NOTES Rev. B | Page 15 of 16 AD8218 Data Sheet NOTES (c)2011-2013 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D09592-0-4/13(B) Rev. B | Page 16 of 16