bq20851

The bq20851-V1P2 SBS-compliant gas gauge IC for battery pack installation maintains an accurate record of available charge in Li-ion or Li-polymer  atteries. The bq20851-V1P2 monitors capacity and other critical parameters of the battery pack and reports the information to the system host controller over a serial communication bus. It is designed to work with the bq29311 analog front-end (AFE) protection IC to maximize functionality and safety and minimize component count and cost in smart battery circuits. Using information from the bq20851-V1P2, the host controller can anage
remaining battery power to extend the system run time as much as possible.


The bq20851-V1P2 uses an integrating converter with continuous sampling for the measurement of battery charge and discharge currents. Optimized for coulomb counting in portable applications, the self-calibrating integrating converter has a resolution better than 3-nVh and an offset measurement error of less than 1-V (typical). For voltage and temperature reporting, the bq20851-V1P2 uses a 16-bit A-to-D converter. In conjunction with the bq29311, the onboard ADC also monitors individual cell voltages in a battery pack and allows the bq20851-V1P2 to generate the control signals necessary to implement the cell balancing and  the required safety protection for Li-ion and Li-polymer battery chemistries.


The bq20851-V1P2 supports the Smart Battery Data (SBData) commands and charge-control functions. It communicates data using the System Management Bus (SMBus) 2-wire protocol. The data available include the battery's remaining capacity, temperature, voltage, current, and remaining run-time predictions. The bq20851-V1P2 provides LED drivers and a push-button input to depict remaining battery capacity from full to empty in 20%, 25%, or 33% increments with a 3-, 4-, or 5-segment display.


The bq20851-V1P2 contains 512 bytes of internal data flash memory, which store configuration information. The information includes nominal capacity and voltage, self-discharge rate, rate compensation factors, and other programmable cell-modeling factors used to accurately adjust remaining capacity for use-conditions based on time, rate, and temperature. The bq20851-V1P2 also automatically calibrates or learns the true battery capacity in the course of a discharge cycle from programmable near full to near empty levels.