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Getting started with bq76925 analogue front end

Posted: 16 Oct 2014 ?? ?Print Version ?Bookmark and Share

Keywords:battery management system? BMS? bq76925? analogue front end? AFE?

This application note presents the major features of a typical battery management system (BMS) built around the bq76925 analogue front end (AFE). The bq76925 provides 3 analogue outputs that allow a microcontroller to easily monitor cell voltage, current, and temperature. Cell voltages are level-shifted, scaled, and multiplexed to the VCOUT pin. Cell current is monitored through a sense resistor placed in series with the cell stack. The voltage across the sense resistor is amplified and driven to the VIOUT pin. The VTB pin supplies a switched bias to stimulate a thermistor network for temperature measurement.

A microcontroller (MCU) with an analogue-to-digital converter (ADC) is required to complete the measurement system. The MCU accesses registers in the AFE through an I2C interface to control the AFE functions and state. The AFE supplies a low-drift reference for accurate A/D conversions. Calibration constants (also called correction factors) stored in the AFE ROM are read by the MCU and applied to the ADC results to achieve high measurement accuracy.

The bq76925 supplies a 3.3-V regulated output for powering the MCU. The AFE also includes integrated cell balancing FETs that are under MCU control. Finally, the AFE's on-board comparator signals an over-current condition to the MCU for fast fault response.

View the PDF document for more information.

Originally published by Texas Instruments Inc. at as "Getting Started With the bq76925".

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