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Application Report
SLUA619–July 2014
Getting Started With the bq76925
John M Ross ............................................................................................................. PWR BMS HCE
ABSTRACT
The bq76925 is combined with a microcontroller to build a complete battery management system. Key
aspects of the system include the microcontroller, filtering and protection, communications, measurement,
and power management. Important considerations are discussed that will aid in the design of the
hardware and firmware of the battery management system.
Contents
1 System Overview ............................................................................................................ 2
1.1 MCU Requirements................................................................................................. 2
2 External Filtering and Protection........................................................................................... 3
2.1 Input Filters .......................................................................................................... 3
2.2 Output Filters........................................................................................................ 4
3 Communications System ................................................................................................... 4
3.1 Addressing........................................................................................................... 5
3.2 CRC Generation .................................................................................................... 5
4 Measurement System....................................................................................................... 5
4.1 Correction Factor Concept......................................................................................... 6
4.2 Reference Voltage.................................................................................................. 6
4.3 Voltage Measurement.............................................................................................. 7
4.4 Current Measurement.............................................................................................. 8
4.5 Temperature Measurement........................................................................................ 8
5 Power Management......................................................................................................... 9
6 Low Dropout (LDO) Regulator ............................................................................................. 9
7 Balancing and Open Cell Detection...................................................................................... 10
8 References.................................................................................................................. 10
List of Figures
1 Example Battery Management System Using the bq76925 ........................................................... 2
2 Filtering a Noisy Input Signal............................................................................................... 4
3 I
2
C Write Transaction........................................................................................................ 4
4 I
2
C Read Transaction........................................................................................................ 4
5 Ratiometric Temperature Measurement .................................................................................. 9
6 V3P3 Load Filter............................................................................................................ 10
List of Tables
1 Combined Addresses for all Named bq76925 Registers............................................................... 5
2 Assembled Integer Gain Correction Factors ............................................................................. 6
3 Assembled Integer Offset Correction Factors............................................................................ 6
1
SLUA619–July 2014 Getting Started With the bq76925
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