Datasheet AD8451 (Analog Devices)

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Low Cost, Precision Analog Front End and Controller for Battery Test/Formation Systems Data Sheet AD8451 FEATURES GENERAL DESCRIPTION Integrated constant current and voltage modes with
The AD8451 is a precision analog front end and control er for
automatic switchover
testing and monitoring battery cells. A precision fixed gain
Charge and discharge modes
instrumentation amplifier (IA) measures the battery charge/
Precision voltage and current measurement
discharge current, and a fixed gain difference amplifier (DA)
Integrated precision control feedback blocks
measures the battery voltage (see Figure 1). Internal laser
Precision interface to PWM or linear power converters
trimmed resistor networks set the gains for the IA and the DA,
Fixed gain settings
optimizing the performance of the AD8451 over the rated
Current sense gain: 26 V/V (typ)
temperature range. The IA gain is 26 V/V and the DA gain is
Voltage sense gain: 0.8 V/V (typ)
0.8 V/V.
Excellent ac and dc performance
Voltages at the ISET and VSET inputs set the desired constant
Maximum offset voltage drift: 0.9 µV/°C
current (CC) and constant voltage (CV) values. CC to CV
Maximum gain drift: 3 ppm/°C
switching is automatic and transparent to the system.
Low current sense amplifier input voltage noise: 9 nV/√Hz typ Current sense CMRR: 108 dB min
A TTL logic level input, MODE, selects the charge or discharge
TTL compliant logic
mode (high for charge, and low for discharge). An analog output, VCTRL, interfaces directly with the Analog Devices, Inc., ADP1972 pulse-width modulation (PWM) control er.
APPLICATIONS
The AD8451 simplifies designs by providing excellent accuracy,
Battery cell formation and testing
performance over temperature, flexibility with functionality,
Battery module testing
and overall reliability in a space-saving package. The AD8451 is available in an 80-lead, 14 mm × 14 mm × 1.40 mm LQFP and is rated for an operating temperature of −40°C to +85°C.
FUNCTIONAL BLOCK DIAGRAM ISREFH/ ISREFL ISMEA ISET IVE0/IVE1 VINT AD8451 ISVP CONSTANT VCLP CURRENT LOOP MUX 26 FILTER ×1 VCTRL ISVN CURRENT VCLN SENSE IA (CHARGE/ MODE DISCHARGE) SWITCHING VOLTAGE BVP SENSE DA VOLTAGE VREF REFERENCE 0.8 CONSTANT VOLTAGE LOOP BVN FILTER
001
BVREFH/ BVMEA VSET VVE0/ VVP0 VSETBF VINT BVREFL VVE1
12137- Figure 1.
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Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION FUNCTIONAL BLOCK DIAGRAM TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS IA CHARACTERISTICS DA CHARACTERISTICS CC AND CV LOOP FILTER AMPLIFIERS, AND VSET BUFFER VINT BUFFER REFERENCE CHARACTERISTICS THEORY OF OPERATION OVERVIEW INSTRUMENTATION AMPLIFIER (IA) Reversing Polarity When Charging and Discharging IA Offset Option Battery Reversal and Overvoltage Protection DIFFERENCE AMPLIFIER (DA) CC AND CV LOOP FILTER AMPLIFIERS Compensation VINT Buffer MODE PIN, CHARGE AND DISCHARGE CONTROL APPLICATIONS INFORMATION FUNCTIONAL DESCRIPTION POWER SUPPLY CONNECTIONS CURRENT SENSE IA CONNECTIONS Current Sensors Optional Low-Pass Filter VOLTAGE SENSE DA CONNECTIONS Reverse Battery Conditions BATTERY CURRENT AND VOLTAGE CONTROL INPUTS (ISET AND VSET) LOOP FILTER AMPLIFIERS CONNECTING TO A PWM CONTROLLER (VCTRL PIN) STEP-BY-STEP DESIGN EXAMPLE Step 1: Design the Switching Power Converter Step 2: Identify the Control Voltage Range of the ADP1972 Step 3: Determine the Control Voltage for the CV Loop Step 4: Determine the Control Voltage for the CC Loop and the Shunt Resistor Step 5: Choose the Control Voltage Sources Step 6: Select the Compensation Devices EVALUATION BOARD INTRODUCTION FEATURES AND TESTS EVALUATING THE AD8451 Test the Instrumentation Amplifier 20 mV Offset at IMEAS Output Test the Difference Amplifier 5 mV Offset at BVMEAS Output CC and CV Integrator Tests Loop Compensation SCHEMATIC AND ARTWORK OUTLINE DIMENSIONS ORDERING GUIDE