ANALOG DEVICES AD8218

Zero Drift, Bidirectional Current Shunt Monitor AD8218 FEATURES FUNCTIONAL BLOCK DIAGRAM V S High common-mode voltage range R4 4 V to 80 V operating AD8218 −0.3 V to 85 V survival R1 Buffered output voltage –IN OUT Gain = 20 V/V +IN Wide operating temperature range: −40°C to +125°C R2 LDO R3 Excellent ac and dc performance ENB ±100 nV/°C typical offset drift ±50 µV typical offset GND REF ±5 ppm/°C typical gain drift Figure 1. 110 dB typical CMRR at dc 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 The AD8218 offers breakthrough performance throughout the amplifier. It features a set gain of 20 V/V, with a maximum −40°C to +125°C temperature range. It features a zero-drift core, ±0.35% gain error over the entire temperature range. The which leads to a typical offset drift of ±100 nV/°C throughout buffered output voltage directly interfaces with any typical the operating temperature range and the common-mode voltage converter. The AD8218 offers excellent input common-mode range. Special attention is devoted to output linearity being rejection from 4 V to 80 V. The AD8218 performs bidirectional maintained throughout the input differential voltage range of current measurements across a shunt resistor in a variety of 0 mV to ~250 mV. The AD8218 also includes an internal 80 mV industrial and telecom applications, including motor control, reference that can be enabled for optimal dynamic range in battery management, and base station power amplifier bias unidirectional current sense applications. The typical input control. offset voltage is ±50 µV. The AD8218 is offered in an 8-lead MSOP package. Rev. A 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 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. rights of third parties that may result from its use. Specifications subject to change without notice. No Tel: 781.329.4700 www.analog.com license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Fax: 781.461.3113 ©2011 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. 09592-001 AD8218 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 Configuration and Function Descriptions ............................. 5 Outline Dimensions ....................................................................... 13 Typical Performance Characteristics ............................................. 6 Ordering Guide .......................................................................... 13 Theory of Operation ...................................................................... 10 Amplifier Core ............................................................................ 10 REVISION HISTORY 2/11—Rev. 0 to Rev. A Changes to Features .......................................................................... 1 1/11—Revision 0: Initial Version Rev. A | Page 2 of 16 AD8218 SPECIFICATIONS TOPR = −40°C to +125°C, TA = 25°C, RL = 25 kΩ (RL is the output load resistor), input common-mode voltage (VCM) = 4 V, unless otherwise noted. Table 1. Parameter Min Typ Max Unit Test Conditions/Comments GAIN Initial 20 V/V Accuracy ±0.1 % VO ≥ 0.1 V dc, TA Accuracy over Temperature ±0.35 % T OPR Gain vs. Temperature ±5 ppm/°C TOPR VOLTAGE OFFSET 1 Offset Voltage (RTI ) ±200 µV 25°C 1 Over Temperature (RTI ) ±300 µV T OPR Offset Drift ±100 nV/°C TOPR INPUT 2 Bias Current 130 µA TA, input common mode = 4 V, VS = 4 V 220 µA T , input common mode = 4 V, V = 4 V OPR S Common-Mode Input Voltage Range 4 80 V Common-mode continuous 3 Differential Input Voltage Range 0 250 mV Differential input voltage Common-Mode Rejection (CMRR) 90 110 dB T OPR OUTPUT Output Voltage Range Low 0.01 V Output Voltage Range High V − 0.1 V T S A Output Impedance 2 Ω INTERNAL REFERENCE (ENB PIN CONNECTED TO GND) Voltage at OUT with a differential input of Initial Value 80 mV 0 V and a common-mode input of 4 V 1 Offset (RTI ) −150 +150 µV 4 VS = NC or VS = 5 V Offset Drift (RTO ) ±10 µV/°C REFERENCE INPUT (REF, PIN 7) Input Impedance 1.5 MΩ Dependent on VREF/1.5 MΩ Input Current 3 60 µA Input Voltage Range 0 5 V ENB not connected to GND Input-to-Output Gain 1 ± 0.0001 V/V DYNAMIC RESPONSE Small-Signal −3 dB Bandwidth 450 kHz Slew Rate 1 V/µs NOISE 1 0.1 Hz to 10 Hz (RTI ) 2.3 µV p-p 1 Spectral Density, 1 kHz (RTI ) 110 nV/√Hz POWER SUPPLY Operating Range (Pin 2 Floating) 4 80 V Power regulated from common mode, V pin floating S VS Range (Pin 2) 4 5.5 V VS must be less than 5.5 V if standalone supply is used Quiescent Current over Temperature 800 µA Throughout input common mode TOPR Power Supply Rejection Ratio (PSRR) 90 110 dB TEMPERATURE RANGE For Specified Performance −40 +125 °C 1 RTI = referred to input. 2 Refer to Figure 8 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. Rev. A | Page 3 of 16 AD8218 ABSOLUTE MAXIMUM RATINGS Table 2. Stresses above those listed under Absolute Maximum Ratings Parameter Rating may cause permanent damage to the device. This is a stress Maximum Input Voltage ( +IN, −IN to GND) −0.3 V to 85 V rating only; functional operation of the device at these or any Differential Input Voltage (+IN to –IN) ±5 V other conditions above those indicated in the operational Human Body Model (HBM) ESD Rating ±2000 V section of this specification is not implied. Exposure to absolute Operating Temperature Range (TOPR) −40°C to +125°C maximum rating conditions for extended periods may affect Storage Temperature Range −65°C to +150°C device reliability. Output Short-Circuit Duration Indefinite ESD CAUTION Rev. A | Page 4 of 16 AD8218 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS +IN 1 8 –IN AD8218 V 2 7 REF S TOP VIEW ENB 3 6 NC (Not to Scale) GND 4 5 OUT NC = NO CONNECT. DO NOT CONNECT TO THIS PIN. Figure 2. Pin Configuration Table 3. Pin Function Descriptions Pin No. Mnemonic Description 1 +IN Noninverting Input. 2 V Supply Pin. Bypass with a standard 0.1 μF capacitor. S 3 ENB Connect to GND to enable the internal 80 mV reference. 4 GND Ground. 5 OUT Output. 6 NC Do not connect to this pin. 7 REF Reference Input. Connect to a low impedance voltage. 8 −IN Inverting Input. Rev. A | Page 5 of 16 09592-002 AD8218 TYPICAL PERFORMANCE CHARACTERISTICS 40 30 27 38 24 36 21 34 18 15 32 12 30 9 28 6 26 3 0 24 –40 –20 0 20 40 60 80 100 120 140 1k 10k 100k 1M FREQUENCY (Hz) TEMPERATURE (°C) Figure 3. Typical Input Offset vs. Temperature Figure 6. Typical Small-Signal Bandwidth (VOUT = 200 mV p-p) 140 10 9 130 8 7 120 6 5 110 4 100 3 2 90 1 –40°C 80 0 +25°C +125°C –1 70 –2 –3 60 –4 50 –5 0 5 10 15 20 25 30 35 40 45 50 100 1000 10k 100k 1M DIFFERENTIAL INPUT (mV) FREQUENCY (Hz) Figure 4. Typical CMRR vs. Frequency Figure 7. Total Output Error vs. Differential Input Voltage 500 800 450 700 +IN 400 600 350 500 300 400 250 300 200 200 100 150 –IN 0 100 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 –40 –20 0 20 40 60 80 100 120 INPUT COMMON-MODE VOLTAGE (V) TEMPERATURE (°C) Figure 5. Typical Gain Error vs. Temperature Figure 8. Input Bias Current vs. Input Common-Mode Voltage (Differential Input Voltage = 5 mV, V = NC) S Rev. A | Page 6 of 16 V (µV) CMRR (dB) OSI GAIN ERROR (ppm) 09592-005 09592-004 09592-003 INPUT BIAS CURRENT (µA) MAGNITUDE (dB) TOTAL OUTPUT ERROR (%) 09592-007 09592-006 09592-008 AD8218 500 INPUT 5mV/DIV 450 400 OUTPUT 350 100mV/DIV 300 250 200 1µs/DIV –40 –20 0 20 40 60 80 100 120 TEMPERATURE (°C) Figure 9. Supply Current vs. Temperature (V = 5 V, V = 12 V) Figure 12. Fall Time (Differential Input = 10 mV) S CM INPUT 100mV/DIV INPUT 5mV/DIV OUTPUT 2V/DIV OUTPUT 100mV/DIV 1µs/DIV 5µs/DIV Figure 10. Rise Time (Differential Input = 10 mV) Figure 13. Fall Time (Differential Input = 200 mV) INPUT 200mV/DIV INPUT 100mV/DIV OUTPUT OUTPUT 2V/DIV 2V/DIV 5µs/DIV 5µs/DIV Figure 11. Rise Time (Differential Input = 200 mV) Figure 14. Differential Overload Recovery, Rising Rev. A | Page 7 of 16 SUPPLY CURRENT (µA) 09592-010 09592-009 09592-109 09592-013 09592-012 09592-011 AD8218 9.5 INPUT 9.0 200mV/DIV 8.5 8.0 7.5 OUTPUT 7.0 6.5 2V/DIV 6.0 5.5 5.0 4.5 4.0 5µs/DIV TEMPERATURE (°C) Figure 15. Differential Overload Recovery, Falling Figure 18. Maximum Output Source Current vs. Temperature 5.010 82.0 5.000 81.5 4.990 4.980 81.0 4.970 4.960 80.5 4.950 4.940 80.0 4.930 4.920 79.5 4.910 79.0 4.900 –40 –20 0 20 40 60 80 100 120 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 TEMPERATURE (°C) OUTPUT SOURCE CURRENT (mA) Figure 16. Internal Reference Voltage vs. Temperature Figure 19. Output Voltage Swing from Rail vs. Output Source Current (V = 5 V, V = NC, V = 12 V, Pin 1 (+IN) and Pin 8 (−IN) Shorted, Pin 3 (ENB) S S CM Shorted to Pin 4 (GND)) 12.0 250 11.5 11.0 200 10.5 10.0 9.5 150 9.0 8.5 8.0 100 7.5 7.0 6.5 50 6.0 5.5 5.0 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 –40 –30 –20 –10 0 10 20 30 40 50 60 70 80 90 100 110 120 OUTPUT SINK CURRENT (mA) TEMPERATURE (°C) Figure 17. Maximum Output Sink Current vs. Temperature Figure 20. Output Voltage Range from GND vs. Output Sink Current Rev. A | Page 8 of 16 MAXIMUM OUTPUT SINK CURRENT (mA) REFERENCE RTO (mV) 09592-014 09592-015 09592-116 OUTPUT VOLTAGE SWING FROM RAIL (V) OUTPUT VOLTAGE RANGE FROM GND (V) MAXIMUM OUTPUT SOURCE CURRENT (mA) –40 –30 –20 –10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 09592-018 09592-016 09592-017 AD8218 500 INPUT 400 50V/DIV 300 OUTPUT 200 1V/DIV 100 0 500ns/DIV –4 –3 –2 –1 0 1 2 3 4 GAIN DRIFT (ppm/°C) Figure 21. Common-Mode Step Response, Rising Figure 24. Gain Drift Distribution 140 INPUT 120 50V/DIV 100 OUTPUT 80 1V/DIV 60 40 20 0 1µs/DIV –0.6 –0.4 –0.2 0 0.2 0.4 0.6 OFFSET DRIFT (µV/°C) Figure 25. Input Offset Drift Distribution Figure 22. Common-Mode Step Response, Falling 180 250 150 200 120 150 90 100 60 50 30 0 0 –200 –100 0 100 200 –5 0 5 10 15 V (µV) INTERNAL REF OFFSET DRIFT (µV/°C) OSI Figure 23. Input Offset Distribution Figure 26. Internal REF Offset Drift Distribution, Referred to Output (RTO) Rev. A | Page 9 of 16 COUNT 09592-020 09592-019 09592-021 COUNT COUNT COUNT 09592-024 09592-023 09592-022 AD8218 THEORY OF OPERATION The AD8218 is configured as a difference amplifier. The AMPLIFIER CORE transfer function is In typical applications, the AD8218 amplifies a small differential OUT = ((R4/R1) × (V1 − V2)) + VREF input voltage generated by the load current flowing through a shunt resistor. The AD8218 rejects high common-mode vol- Resistors R4 and R1 are matched to within 0.01% and have tages (up to 80 V) and provides a ground-referenced, buffered values of 1.5 MΩ and 75 kΩ, respectively, meaning an input- output. Figure 27 shows a simplified schematic of the AD8218. to-output total gain of 20 V/V for the AD8218. The difference between V and V is the voltage across the shunt resistor, or 1 2 5V C F V . Therefore, the input-to-output transfer function of the IN I LOAD AD8218 is V GND S I CHARGE R4 OUT (V) = (20 × VIN) + VREF AD8218 The AD8218 accurately amplifies the input differential signal, –IN R1 V rejecting high voltage common modes ranging from 4 V to 80 V. 2 LOAD SHUNT OUT +IN V 1 The main amplifier uses a novel zero-drift architecture, providing R2 4V R3 LDO the end user with breakthrough temperature stability. The TO 80V ENB offset drift is typically less than ±100 nV/°C. This performance leads to optimal accuracy and dynamic range. REF GND V REF OUTPUT CLAMPING After the input common-mode voltage in the application is Figure 27. Simplified Schematic 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. A | Page 10 of 16 09592-027 AD8218 APPLICATION NOTES SUPPLY (V ) CONNECTIONS ENABLE PIN (ENB) OPERATION S The AD8218 includes an internal LDO, which allows the user The AD8218 includes an internal reference that can be enabled to leave the V pin floating, powering the AD8218 directly from by connecting Pin 3 (ENB) to ground. This mode of operation S the voltage present at Pin 1 (+IN), provided this voltage is in the is shown in Figure 30. 4 V to 80 V range. A typical connection for the part in this I LOAD configuration is shown in Figure 28. 4V SHUNT I I BATTERY TO LOAD CHARGE LOAD 80V +IN –IN 4V SHUNT BATTERY V REF TO LOAD S 80V –IN AD8218 +IN OUT V ENB REF S 2.5V GND AD8218 OUT ENB GND Figure 30. Enabling the Internal 80 mV Reference In this configuration, the internal 80 mV reference is activated, Figure 28. Operation with No V Connection S and the output of the AD8218 is 80 mV when the differential The AD8218 can also be powered from a separate low impedance input voltage is 0 V and the voltage at Pin 7 (REF) is also 0 V. This supply at Pin 2 (VS); however, this voltage can only be in the 4 V internal reference is useful in unidirectional current measurements to 5.5 V range. In cases where the high voltage bus is susceptible where the current being monitored has a very wide range. Setting to noise, transients, or high voltage fluctuations and a 5 V supply is the output starting point to 80 mV means that when the load available, the AD8218 can be used in the mode depicted in current through the shunt resistor is 0 A, the output is 80 mV. Figure 29. This ensures that the output errors due to initial offset and the I I LOAD CHARGE output saturation range of the amplifier are overcome. In this mode, the transfer function of the AD8218 becomes 4V SHUNT BATTERY TO LOAD 80V OUT (V) = OUT (V) = (20 × V ) + 0.08 V IN +IN –IN V S REF If Pin 3 is connected to ground, and therefore the internal C 5V 2.5V F AD8218 reference is enabled, 80 mV must always be added to the OUT ENB transfer function of the AD8218. GND Figure 29. 5 V Supply Operation Rev. A | Page 11 of 16 09592-028 09592-029 09592-030 AD8218 APPLICATIONS INFORMATION V S UNIDIRECTIONAL HIGH-SIDE CURRENT SENSING I LOAD R4 AD8218 In the unidirectional high-side current sensing configuration, the shunt resistor is referenced to the battery (see Figure 31). –IN R1 V High voltage is present at the inputs of the current sense amplifier. 2 LOAD SHUNT OUT +IN When the shunt is battery referenced, the AD8218 produces a V 1 R2 LDO R3 linear ground-referenced analog output. The supply pin, VS, of the BATTERY ENB (4V TO 80V) AD8218 can either be connected to a 5 V supply or left floating (see the Supply (VS) Connections section). REF GND V S 2.5V I LOAD R4 AD8218 Figure 33. Bidirectional Operation Using a 2.5 V Reference Input –IN R1 V 2 SHUNT OUT LOAD The output transfer function curve for bidirectional operation +IN V 1 using a 2.5 V reference input is shown in Figure 34. R2 R3 BATTERY LDO ENB (4V TO 80V) 5.0 4.5 REF GND 4.0 3.5 Figure 31. Unidirectional Operation with ENB Connected to GND 3.0 The output transfer function curve for unidirectional operation 2.5 with ENB connected to GND is shown in Figure 32. 2.0 320 1.5 280 1.0 0.5 240 0 200 –0.15 –0.10 –0.05 0 0.05 0.10 0.15 INPUT VOLTAGE (V) 160 Figure 34. 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 40 the shunt resistor is referenced to a battery and the current 0 0 1 2 3 4 5 6 7 8 9 10 flowing is bidirectional (as shown in Figure 35), the AD8218 INPUT VOLTAGE (mV) monitors the current with no additional supply pin necessary. Figure 32. Output Transfer Function with ENB Connected to GND BATTERY BIDIRECTIONAL HIGH-SIDE CURRENT SENSING I MOTOR Inputting a voltage at Pin 7 (REF) offsets the output of the AD8218 and allows for bidirectional current sensing. The transfer function MOTOR +IN –IN from the REF pin to the output is 1 V/V. For example, a 2.5 V REF V REF S input offsets the output of the AD8218 to 2.5 V. See Figure 33 V REF AD8218 for typical connections. The user must ensure that the voltage OUT ENB applied at Pin 7 (REF) is from a low impedance source. GND Figure 35. High-Side Current Sensing in Motor Control Rev. A | Page 12 of 16 OUTPUT VOLTAGE (mV) 09592-032 09592-031 OUTPUT VOLTAGE (V) 09592-035 09592-034 09592-033 AD8218 OUTLINE DIMENSIONS 3.20 3.00 2.80 8 5 5.15 3.20 4.90 3.00 4.65 1 2.80 4 PIN 1 IDENTIFIER 0.65 BSC 0.95 15° MAX 0.85 1.10 MAX 0.75 0.80 0.15 0.23 6° 0.55 0.40 0.05 0.09 0° 0.40 0.25 COPLANARITY 0.10 COMPLIANT TO JEDEC STANDARDS MO-187-AA Figure 36. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters ORDERING GUIDE 1 Model Temperature Range Package Description Package Option Branding AD8218BRMZ −40°C to +125°C 8-Lead Mini Small Outline Package [MSOP] RM-8 Y3K AD8218BRMZ-RL −40°C to +125°C 8-Lead Mini Small Outline Package [MSOP] RM-8 Y3K 1 Z = RoHS Compliant Part. Rev. A | Page 13 of 16 10-07-2009-B AD8218 NOTES Rev. A | Page 14 of 16 AD8218 NOTES Rev. A | Page 15 of 16 AD8218 NOTES ©2011 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D09592-0-2/11(A) Rev. A | Page 16 of 16