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 controller 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 V/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 A TTL logic level input, MODE, selects the charge or discharge Current sense CMRR: 108 dB min mode (high for charge, and low for discharge). An analog output, TTL compliant logic VCTRL, interfaces directly with the Analog Devices, Inc., ADP1972 pulse-width modulation (PWM) controller. 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 40C to +85C. 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 BVREFH/ BVMEA VSET VVE0/ VVP0 VSETBF VINT BVREFL VVE1 Figure 1. Rev. 0 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 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 2014 Analog Devices, Inc. All rights reserved. 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. Technical Support www.analog.com 12137-001AD8451 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 MODE Pin, Charge and Discharge Control ........................... 21 Applications ....................................................................................... 1 Applications Information .............................................................. 22 General Description ......................................................................... 1 Functional Description .............................................................. 22 Functional Block Diagram .............................................................. 1 Power Supply Connections ....................................................... 23 Revision History ............................................................................... 2 Current Sense IA Connections ................................................. 23 Specifications ..................................................................................... 3 Voltage Sense DA Connections ................................................ 23 Absolute Maximum Ratings ............................................................ 6 Battery Current and Voltage Control Inputs (ISET and VSET) ....................................................................................................... 23 Thermal Resistance ...................................................................... 6 Loop Filter Amplifiers ............................................................... 24 ESD Caution .................................................................................. 6 Connecting to a PWM Controller (VCTRL Pin) ...................... 24 Pin Configuration and Function Descriptions ............................. 7 Step-by-Step Design Example................................................... 24 Typical Performance Characteristics ............................................. 9 Evaluation Board ............................................................................ 26 IA Characteristics ......................................................................... 9 Introduction ................................................................................ 26 DA Characteristics ..................................................................... 11 Features and Tests ....................................................................... 26 CC and CV Loop Filter Amplifiers, and VSET Buffer .......... 13 Evaluating the AD8451 .............................................................. 27 VINT Buffer ................................................................................ 15 Schematic and Artwork ............................................................. 28 Reference Characteristics .......................................................... 16 Outline Dimensions ....................................................................... 32 Theory of Operation ...................................................................... 17 Ordering Guide .......................................................................... 32 Overview ...................................................................................... 17 Instrumentation Amplifier (IA) ............................................... 18 Difference Amplifier (DA) ........................................................ 19 CC and CV Loop Filter Amplifiers .......................................... 19 REVISION HISTORY 3/14Revision 0: Initial Version Rev. 0 Page 2 of 32