AD8211

High Voltage Current Shunt Monitor AD8211 FEATURES ±4000 V HBM ESD High common-mode voltage range −2 V to +65 V operating −3 V to +68 V survival Buffered output voltage Wide operating temperature range 5-lead SOT: −40°C to +125°C Excellent ac and dc performance 5 μV/°C typical offset drift −13 ppm/°C typical gain drift 120 dB typical CMRR at dc FUNCTIONAL BLOCK DIAGRAM VIN+ VIN– A1 PROPRIETARY OFFSET CIRCUITRY V+ OUT G = +20 APPLICATIONS High-side current sensing Motor controls Transmission controls Engine management Suspension controls Vehicle dynamic controls DC-to-dc converters GND Figure 1. GENERAL DESCRIPTION The AD8211 is a high voltage, precision current shunt amplifier. It features a set gain of 20 V/V, with a typical ±0.5% gain error over the entire temperature range. The buffered output voltage directly interfaces with any typical converter. Excellent commonmode rejection from −2 V to +65 V is independent of the 5 V supply. The AD8211 performs unidirectional current measurements across a shunt resistor in a variety of industrial and automotive applications, such as motor control, solenoid control, or battery management. Special circuitry 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. The AD8211 has an operating temperature range of −40°C to +125°C and is offered in a small 5-lead SOT package. 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 ©2007 Analog Devices, Inc. All rights reserved. 06824-001 AD8211 AD8211 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 Application Notes ........................................................................... 11 Output Linearity......................................................................... 11 Applications Information .............................................................. 12 High-Side Current Sense with a Low-Side Switch................. 12 High-Side Current Sensing ....................................................... 12 Low-Side Current Sensing ........................................................ 12 Outline Dimensions ....................................................................... 13 Ordering Guide .......................................................................... 13 REVISION HISTORY 7/07—Revision 0: Initial Version Rev. 0 | Page 2 of 16 AD8211 SPECIFICATIONS TOPR = −40°C to +125°C, TA = 25°C, VS = 5 V, RL = 25 kΩ (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) Over Temperature (RTI) Offset Drift INPUT Input Impedance Differential Common Mode Common-Mode Input Voltage Range Differential Input Voltage Range Common-Mode Rejection 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 Spectral Density, 1 kHz, RTI POWER SUPPLY Operating Range Quiescent Current Over Temperature Power Supply Rejection Ratio TEMPERATURE RANGE For Specified Performance 1 2 Min Typ 20 Max Unit V/V % % ppm/°C mV mV μV/°C Conditions ±0.25 ±0.35 −13 ±1 ±2.2 5 VO ≥ 0.1 V dc TOPR TOPR 1 25°C TOPR TOPR 2 5 5 3.5 −2 100 80 0.1 250 120 90 0.05 4.95 2 500 4.5 7 70 4.5 1.2 76 −40 +125 5.5 2.0 +65 kΩ MΩ kΩ V mV dB dB V V Ω kHz V/μs μV p-p nV/√Hz V mA dB °C Common-mode voltage > 5 V Common-mode voltage < 5 V Common-mode continuous Differential input voltage TA, f = dc, VCM > 5 V, see Figure 5 TA, f = dc, VCM < 5 V, see Figure 5 4.9 VCM > 5 V 3 , see Figure 12 The mean of the gain drift distribution is typically −13 ppm/°C, with a σ = 3 ppm/°C. The mean of the offset drift distribution is typically +5 μV/°C, with a σ = 3 μV/°C. 3 When the input common-mode voltage is less than 5 V, the supply current increases, which can be calculated by IS = −0.275 (VCM) + 2.5. Rev. 0 | Page 3 of 16 AD8211 ABSOLUTE MAXIMUM RATINGS Table 2. Parameter Supply Voltage Continuous Input Voltage Reverse Supply Voltage HBM (Human Body Model) ESD Rating CDM (Charged Device Model) ESD Rating Operating Temperature Range Storage Temperature Range Output Short-Circuit Duration Rating 12.5 V −3 V to +68 V −0.3 V ±4000 V ±1000 V −40°C to +125°C −65°C to +150°C 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 AD8211 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS OUT 1 5 V+ AD8211 1 2 5 GND 2 VIN+ 3 TOP VIEW (Not to Scale) 06824-002 4 VIN– NC = NO CONNECT Figure 3. Pin Configuration Figure 2. Metallization Diagram Table 3. Pin Function Descriptions Pin No. 1 2 3 4 5 Mnemonic OUT GND VIN+ VIN− V+ X −277 −140 −228 +229 +264 Y +466 +466 −519 −519 +466 Description Buffered Output. Ground. Noninverting Input. Inverting Input. Supply. 06824-030 3 4 Rev. 0 | Page 5 of 16 AD8211 TYPICAL PERFORMANCE CHARACTERISTICS 1.2 1.0 0.8 0.6 0.4 40 35 30 25 20 15 VOSI (mV) 0.2 0 –0.2 –0.4 –0.6 –0.8 –1.0 –1.2 –40 –20 0 20 40 60 80 100 120 06824-112 GAIN (dB) 10 5 0 –5 –10 –15 –20 06824-107 –25 –30 –35 –40 10k 100k FREQUENCY (Hz) 1M 10M TEMPERATURE (°C) Figure 4. Typical Offset vs. Temperature 140 130 COMMON-MODE VOLTAGE > 5V 120 110 100 COMMON-MODE VOLTAGE < 5V 90 80 06824-114 Figure 7. Typical Small Signal Bandwidth (VOUT = 200 mV p-p) 10 9 TOTAL OUTPUT ERROR (%) 8 7 6 5 4 3 2 1 0 DIFFERENTIAL INPUT VOLTAGE (mV) 06824-118 CMRR (dB) 70 60 10 100 1k 10k 100k 1M 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 250 FREQUNCY (Hz) Figure 5. Typical CMRR vs. Frequency 2500 2000 1500 Figure 8. Total Output Error vs. Differential Input Voltage –510 –515 –520 INPUT BIAS CURRENT (µA) –525 –530 –535 –540 –545 –550 –555 –560 06824-103 GAIN ERROR (PPM) 1000 500 0 –500 –1000 –1500 –2000 –2500 –40 06824-113 VIN+ VIN– –565 –570 0 25 50 75 100 125 150 175 200 225 DIFFERENTIAL INPUT VOLTAGE (mV) –20 0 20 40 60 80 100 120 250 TEMPERATURE (°C) Figure 6. Typical Gain Error vs. Temperature Figure 9. Input Bias Current vs. Differential Input Voltage, VCM = 0 V Rev. 0 | Page 6 of 16 AD8211 110 100 INPUT BIAS CURRENT (µA) 100mV/DIV 90 VIN+ 80 INPUT 1V/DIV 70 VIN– 60 OUTPUT 06824-104 50 40 0 25 50 75 100 125 150 175 200 225 DIFFERENTIAL INPUT VOLTAGE (mV) 250 TIME (500ns/DIV) Figure 10. Input Bias Current vs. Differential Input Voltage, VCM = 5 V 0.8 0.4 Figure 13. Fall Time INPUT BIAS CURRENT (mA) 0 –0.4 –0.8 –1.2 –1.6 06824-102 INPUT 100mV/DIV OUTPUT 1V/DIV –2.0 –2.4 –5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 INPUT COMMON-MODE VOLTAGE (V) TIME (500ns/DIV) Figure 11. Input Bias Current vs. Input Common-Mode Voltage 4.0 Figure 14. Rise Time 200mV/DIV 3.5 SUPPLY CURRENT (mA) 3.0 INPUT 2.5 2V/DIV 2.0 1.5 06824-101 OUTPUT 06824-109 1.0 –4 –2 0 2 4 6 8 65 COMMON-MODE VOLTAGE (V) TIME (1µs/DIV) Figure 12. Supply Current vs. Common-Mode Voltage Figure 15. Differential Overload Recovery (Falling) Rev. 0 | Page 7 of 16 06824-111 06824-110 AD8211 12.0 INPUT MAXIMUM OUTPUT SINK CURRENT (mA) 11.5 11.0 10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 06824-106 200mV/DIV OUTPUT 2V/DIV 06824-108 6.0 5.5 5.0 –40 –30 –20 –10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 TIME (1µs/DIV) TEMPERATURE (°C) Figure 16. Differential Overload Recovery (Rising) Figure 19. Maximum Output Sink Current vs. Temperature 9.0 MAXIMUM OUTPUT SOURCE CURRENT (mA) 2V/DIV 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 –40 –20 0 20 40 60 80 100 120 140 06824-105 0.01/DIV TIME 5µs/DIV) 06824-120 TEMPERATURE (°C) Figure 17. Settling Time (Falling) Figure 20. Maximum Output Source Current vs. Temperature 5.0 4.6 2V/DIV OUTPUT VOLTAGE RANGE (V) 06824-119 4.2 3.8 3.4 3.0 2.6 2.2 1.8 1.4 1.0 0 1 2 3 4 5 6 7 8 9 OUTPUT SOURCE CURRENT (mA) 06824-117 0.01/DIV TIME 5µs/DIV) Figure 18. Settling Time (Rising) Figure 21. Output Voltage Range vs. Output Source Current Rev. 0 | Page 8 of 16 AD8211 2.0 OUTPUT VOLTAGE RANGE FROM GND (V) 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0 1 2 3 4 5 6 7 8 9 10 11 12 OUTPUT SINK CURRENT (mA) 06824-116 Figure 22. Output Voltage Range from GND vs. Output Sink Current Rev. 0 | Page 9 of 16 AD8211 THEORY OF OPERATION In typical applications, the AD8211 amplifies a small differential input voltage generated by the load current flowing through a shunt resistor. The AD8211 rejects high common-mode voltages (up to 65 V) and provides a ground-referenced, buffered output that interfaces with an analog-to-digital converter (ADC). Figure 23 shows a simplified schematic of the AD8211. ISHUNT RSHUNT IIN R1 R A load current flowing through the external shunt resistor produces a voltage at the input terminals of the AD8211. The input terminals are connected to Amplifier A1 by Resistor R and Resistor R1. The inverting terminal, which has very high input impedance is held to (VCM) − (ISHUNT × RSHUNT) because negligible current flows through Resistor R. Amplifier A1 forces the noninverting input to the same potential. Therefore, the current that flows through Resistor R1, is equal to IIN = (ISHUNT × RSHUNT)/R1 This current (IIN) is converted back to a voltage via ROUT. The output buffer amplifier has a gain of 20 V/V and offers excellent accuracy as the internal gain setting resistors are precision trimmed to within 0.01% matching. The resulting output voltage is equal to VOUT = (ISHUNT × RSHUNT) × 20 A1 PROPRIETARY OFFSET CIRCUITRY Q1 V+ VOUT = (ISHUNT × RSHUNT ) × 20 ROUT G = +20 GND Figure 23. Simplified Schematic 06824-022 AD8211 Rev. 0 | Page 10 of 16 AD8211 APPLICATION NOTES OUTPUT LINEARITY In all current sensing applications, and especially in automotive and industrial environments 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 AD8211 contains specific circuitry on the input stage, which ensures that even when the differential input voltage is very small, and the common-mode voltage is also low (below the 5 V supply), the input-to-output linearity is maintained. Figure 24 shows the input differential voltage vs. the corresponding output voltage at different common modes. 200 180 160 Regardless of the common mode, the AD8211 provides a correct output voltage when the input differential is at least 2 mV, which is due to the voltage range of the output amplifier that can go as low as 33 mV typical. The specified minimum output amplifier voltage is 100 mV to provide sufficient guardbands. The ability of the AD8211 to work with very small differential inputs, regardless of the common-mode voltage, allows for more dynamic range, accuracy, and flexibility in any current sensing application. OUTPUT VOLTAGE (mV) 140 120 100 80 60 40 20 0 0 1 2 3 4 5 6 7 8 9 10 DIFFERENTIAL INPUT VOLTAGE (mV) IDEAL VOUT (mV) VOUT (mV) @ VCM = 0V VOUT (mV) @ VCM = 65V Figure 24. Gain Linearity Due to Differential and Common-Mode Voltage 06824-115 Rev. 0 | Page 11 of 16 AD8211 APPLICATIONS INFORMATION HIGH-SIDE CURRENT SENSE WITH A LOW-SIDE SWITCH In such load control configurations, the PWM-controlled 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 25). An advantage of placing the shunt on the high side is that the entire current, including the recirculation current, can be measured because 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. 1 3 2 1 3 OVERCURRENT DETECTION (