High Voltage, Current Shunt Monitor AD825 FEATURES ±4 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 8-Lead SOIC_N: 4 C to +25 C Excellent ac and dc performance 6 μv/ C typical offset drift 8 ppm/ C typical gain drift 2 db typical CMRR at dc APPLICATIONS High-side current sensing Motor controls Transmission controls Engine management Suspension controls Vehicle dynamic controls DC-to-dc converters FUNCTIONAL BLOCK DIAGRAM IN+ A IN PROPRIETARY OFFSET CIRCUITRY GND Figure. G = +2 AD825 V+ OUT 723- GENERAL DESCRIPTION The AD825 is a high voltage, precision current shunt monitor. It features a set gain of 2 V/V, with a maximum ±.3% 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 AD825 performs unidirectional current measurements across a shunt resistor in a variety of industrial and automotive applications, such as motor controls, solenoid controls, or battery management. Special circuitry is devoted to output linearity being maintained throughout the input differential voltage range of mv to 25 mv, regardless of the common-mode voltage present. The AD825 has an operating temperature range of 4 C to +25 C and is offered in a small 8-lead SOIC_N package. Rev. 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 96, Norwood, MA 262-96, U.S.A. Tel: 78.329.47 www.analog.com Fax: 78.46.33 28 Analog Devices, Inc. All rights reserved.
TABLE OF CONTENTS Features... Applications... Functional Block Diagram... General Description... 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... Application Notes... Output Linearity... Applications Information... 2 High-Side Current Sensing with a Low-Side Switch... 2 High-Side Current Sensing... 2 Low-Side Current Sensing... 2 Outline Dimensions... 3 Ordering Guide... 3 REVISION HISTORY /8 Revision : Initial Version Rev. Page 2 of 6
SPECIFICATIONS TOPR = 4 C to +25 C, TA = 25 C, VS = 5 V, RL = 25 kω (RL is the output load resistor), unless otherwise noted. Table. Parameter Min Typ Max Unit Conditions GAIN Initial 2 V/V Accuracy ±.5 % VO. V dc, TA Accuracy Over Temperature ±.3 % TOPR Drift 8 5 ppm/ C TOPR VOLTAGE OFFSET Offset Voltage, RTI ± mv TA Over Temperature, RTI ±2.5 mv TOPR Drift 5 +6 +8 μv/ C TOPR INPUT Input Impedance Differential 5 kω Common Mode 5 MΩ Common-mode voltage > 5 V 3.5 kω Common-mode voltage < 5 V Common-Mode Input Voltage Range 2 +65 V Common-mode continuous Differential Input Voltage Range 25 mv Differential input voltage Common-Mode Rejection Ratio 2 db TOPR, f = dc to 5 khz, VCM > 5 V 8 9 db TOPR, f = dc to 4 khz, VCM < 5 V OUTPUT Output Voltage Range Low.3 V TA. V TOPR Output Voltage Range High 4.95 V TA 4.9 V TOPR Output Impedance 2 Ω DYNAMIC RESPONSE Small Signal 3 db Bandwidth 45 khz TOPR Slew Rate 4.5 V/μs TA NOISE. Hz to Hz, RTI 7 μv p-p Spectral Density, khz, RTI 7 nv/ Hz POWER SUPPLY Operating Range 4.5 5.5 V Quiescent Current Over Temperature.3 2.2 ma VCM > 5 V, TOPR Power Supply Rejection Ratio 75 db TOPR TEMPERATURE RANGE For Specified Performance 4 +25 C When the input common-mode voltage is less than 5 V, the supply current increases, which can be calculated by IS =.275 (VCM) + 2.5. Rev. Page 3 of 6
ABSOLUTE MAXIMUM RATINGS Table 2. Parameter Supply Voltage Continuous Input Voltage Continuous Differential Input Voltage Reverse Supply Voltage Human Body Model (HBM) ESD Rating Charged Device Model (CDM) ESD Rating Operating Temperature Range Storage Temperature Range Output Short-Circuit Duration Rating 2.5 V 3 V to +68 V.5 V.3 V ±4 V ± V 4 C to +25 C 65 C to +5 C Indefinite ESD CAUTION 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. Rev. Page 4 of 6
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS 8 2 6 5 723-2 Figure 2. Metallization Diagram IN GND 2 NC 3 NC 4 AD825 TOP VIEW (Not to Scale) NC = NO CONNECT 8 7 6 5 +IN NC V+ OUT Figure 3. Pin Configuration 723-3 Table 3. Pin Function Descriptions Pin No. Mnemonic X Y Description IN 228 +59 Inverting Input. 2 GND 273 25 Ground. 3, 4, 7 NC N/A N/A No Connect. 5 OUT +265 466 Buffered Output. 6 V+ +273 266 Supply. 8 +IN +229 +59 Noninverting Input. Rev. Page 5 of 6
TYPICAL PERFORMANCE CHARACTERISTICS V OSI (mv).2..8.6.4.2.2.4.6.8..2 4 2 2 4 6 8 2 TEMPERATURE ( C) Figure 4. Typical Offset Drift vs. Temperature 723-7 GAIN (db) 4 35 3 25 2 5 5 5 5 2 25 3 35 4 k k M M FREQUENCY (Hz) Figure 7. Typical Small Signal Bandwidth (VOUT = 2 mv p-p) 723-8 4 3 9 CMRR (db) 2 9 8 COMMON-MODE VOLTAGE >5V COMMON-MODE VOLTAGE <5V TOTAL OUTPUT ERROR (%) 8 7 6 5 4 3 2 7 6 k k k M FREQUENCY (Hz) Figure 5. Typical CMRR vs. Frequency 723-24 5 5 2 25 3 35 4 45 5 55 6 65 7 75 8 85 9 95 25 DIFFERENTIAL INPUT VOLTAGE (mv) Figure 8. Total Output Error vs. Differential Input Voltage 723-22 25 48 GAIN ERROR (ppm) 2 5 5 5 5 2 INPUT BIAS CURRENT (µa) 49 5 5 52 53 54 55 56 V IN+ V IN 25 4 2 2 4 6 8 2 TEMPERATURE ( C) Figure 6. Typical Gain Error vs. Temperature 723-6 57 25 5 75 25 5 75 2 225 25 DIFFERENTIAL INPUT VOLTAGE (mv) Figure 9. Input Bias Current vs. Differential Input Voltage, VCM = V 723-7 Rev. Page 6 of 6
2 INPUT BIAS CURRENT (µa) 9 8 7 6 IN+ IN 2 mv/div V/DIV INPUT OUTPUT 5 4 25 5 75 25 5 75 2 225 25 DIFFERENTIAL INPUT VOLTAGE (mv) Figure. Input Bias Current vs. Differential Input Voltage, VCM = 5 V 723-6 TIME (4ns/DIV) Figure 3. Fall Time 723-2.8 INPUT BIAS CURRENT (ma).4.4.8.2.6 2 mv/div V/DIV INPUT OUTPUT 2. 2.4 4 2 2 4 6 8 65 INPUT COMMON-MODE VOLTAGE (V) Figure. Input Bias Current vs. Input Common-Mode Voltage 723-4 TIME (4ns/DIV) Figure 4. Rise Time 723-5 4. 3.5 2mV/DIV SUPPLY CURRENT (ma) 3. 2.5 2. 2V/DIV INPUT.5. 4 2 2 4 6 8 65 INPUT COMMON-MODE VOLTAGE (V) Figure 2. Supply Current vs. Common-Mode Voltage 723-5 2 TIME (µs/div) OUTPUT Figure 5. Differential Overload Recovery (Falling) 723-3 Rev. Page 7 of 6
INPUT 2 2 2mV/DIV OUTPUT 2V/DIV TIME (µs/div) Figure 6. Differential Overload Recovery (Rising) 723-4 MAXIMUM OUTPUT SINK CURRENT (ma) 9 8 7 6 5 4 2 2 4 6 8 2 4 TEMPERATURE ( C) Figure 9. Maximum Output Sink Current vs. Temperature 723-2 2V/DIV.%/DIV TIME (4µs/DIV) Figure 7. Settling Time (Falling) 723-9 MAXIMUM OUTPUT SOURCE CURRENT (ma) 9 8 7 6 5 4 4 2 2 4 6 8 2 4 TEMPERATURE ( C) Figure 2. Maximum Output Source Current vs. Temperature 723-5. 2 2V/DIV.%/DIV OUTPUT VOLTAGE RANGE (V) 4.6 4.2 3.8 3.4 3. 2.6 2.2.8 TIME (4µs/DIV) Figure 8. Settling Time (Rising) 723-2.4. 2 3 4 5 6 7 8 9 OUTPUT SOURCE CURRENT (ma) Figure 2. Output Voltage Range vs. Output Source Current 723-8 Rev. Page 8 of 6
2. 24 OUTPUT VOLTAGE RANGE (V).6.2.8.4 COUNT 2 8 5 2 9 6 3 2 3 4 5 6 7 8 9 2 OUTPUT SINK CURRENT (ma) Figure 22. Output Voltage Range from GND vs. Output Sink Current 723-9 6 4 2 8 6 4 2 GAIN DRIFT (ppm/ C) Figure 24. Gain Drift Distribution 723-23 35 3 +25 C +25 C 4 C 6 4 25 2 COUNT 2 5 COUNT 8 6 4 5 2 2 2 V OS (mv) 723-2 2 5 5 5 5 2 OFFSET DRIFT (µv/ C) 723-3 Figure 23. Offset Distribution Figure 25. Offset Drift Rev. Page 9 of 6
THEORY OF OPERATION In typical applications, the AD825 amplifies a small differential input voltage generated by the load current flowing through a shunt resistor. The AD825 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 26 shows a simplified schematic of the AD825. I IN R I SHUNT R SHUNT A R PROPRIETARY OFFSET CIRCUITRY V+ A load current flowing through the external shunt resistor produces a voltage at the input terminals of the AD825. The input terminals are connected to A by R and R. The inverting terminal, which has very high input impedance, is held to (VCM) (ISHUNT RSHUNT) because negligible current flows through R. A forces the noninverting input to the same potential. Therefore, the current that flows through R is equal to IIN = (ISHUNT RSHUNT)/R This current (IIN) is converted back to a voltage via ROUT. The output buffer amplifier has a gain of 2 V/V and offers excellent accuracy as the internal gain setting resistors are precision trimmed to within.% matching. The resulting output voltage is equal to OUT = (ISHUNT RSHUNT) 2 R OUT G = +2 OUT = (I SHUNT R SHUNT ) 2 AD825 GND Figure 26. Simplified Schematic 723-25 Rev. Page of 6
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 AD825 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 27 shows the differential input voltage vs. the corresponding output voltage at different common modes. 2 Regardless of the common mode, the AD825 provides a correct output voltage when the differential input 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 mv to provide sufficient guardbands. The ability of the AD825 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. 8 6 OUTPUT VOLTAGE (mv) 4 2 8 6 4 IDEAL V OUT (mv) 2 V OUT (mv) @ V CM =V V OUT (mv) @ V CM =65V 2 3 4 5 6 7 8 9 DIFFERENTIAL INPUT VOLTAGE (mv) Figure 27. Gain Linearity Due to Differential and Common-Mode Voltage 723-26 Rev. Page of 6
APPLICATIONS INFORMATION HIGH-SIDE CURRENT SENSING 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 28). 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. OVERCURRENT DETECTION (<ns) 5 OUT NC 4 5V 6 7 8 GND NC IN AD824 V REG +IN V S 3 2 5 6 7 8 OUT V+ NC IN+ AD825 NC NC GND IN 4 3 2 5 SHUNT CLAMP DIODE INDUCTIVE LOAD BATTERY 5V BATTERY INDUCTIVE LOAD CLAMP DIODE SWITCH SHUNT Figure 28. Low-Side Switch 8 7 6 5 IN+ NC V+ OUT AD825 IN GND NC NC 4 2 3 54 HIGH-SIDE CURRENT SENSING In this configuration, the shunt resistor is referenced to the battery. High voltage is present at the inputs of the current sense amplifier. In this mode, the recirculation current is again measured and shorts to ground can be detected. When the shunt is battery referenced, the AD825 produces a linear ground-referenced analog output. An AD824 can also be used to provide an overcurrent detection signal in as little as ns (see Figure 29). This feature is useful in high current systems where fast shutdown in over-current conditions is essential. 723-27 SWITCH Figure 29. Battery-Referenced Shunt Resistor LOW-SIDE CURRENT SENSING In systems where low-side current sensing is preferred, the AD825 provides an integrated solution with great accuracy. Ground noise is rejected, CMRR is typically higher than 9 db, and output linearity is not compromised, regardless of the input differential voltage. 5V 5 6 7 8 OUT V+ NC IN+ AD825 NC NC GND IN 4 3 2 5 INDUCTIVE LOAD CLAMP DIODE SHUNT SWITCH BATTERY 723-29 723-28 Figure 3. Ground-Referenced Shunt Resistor Rev. Page 2 of 6
OUTLINE DIMENSIONS 5. (.968) 4.8 (.89) 4. (.574) 3.8 (.497) 8 5 4 6.2 (.244) 5.8 (.2284).25 (.98). (.4) COPLANARITY. SEATING PLANE.27 (.5) BSC.75 (.688).35 (.532).5 (.2).3 (.22) 8.25 (.98).7 (.67).5 (.96).25 (.99).27 (.5).4 (.57) 45 COMPLIANT TO JEDEC STANDARDS MS-2-AA 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 3. 8-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-8) Dimensions shown in millimeters and (inches) 247-A ORDERING GUIDE Model Temperature Range Package Description Package Option AD825YRZ 4 C to +25 C 8-Lead SOIC_N R-8 AD825YRZ-RL 4 C to +25 C 8-Lead SOIC_N, 3 Tape and Reel R-8 AD825YRZ-R7 4 C to +25 C 8-Lead SOIC_N, 7 Tape and Reel R-8 Z = RoHS Compliant Part. Rev. Page 3 of 6
NOTES Rev. Page 4 of 6
NOTES Rev. Page 5 of 6
NOTES 28 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D723--/8() Rev. Page 6 of 6