Both internal and external passive cell balancing options are fully supported by the BQ76920, while external cell balancing is recommended for BQ76930 and BQ76940. It is left to the host controller to determine the exact balancing algorithm to be used in any given system. Each BQ769x0 device provides the cell voltages and balancing drivers to enable this. If using the internal cell balance drivers, up to 50 mA may be balanced per cell. If using external cell balancing, much higher balancing currents may be employed.

To activate a particular cell balancing channel, simply set the corresponding bit for that cell in the CELLBAL1, CELLBAL2, or CELLBAL3 register. For example, VC1–VC0 is enabled by setting [CB1], while VC12–VC11 is set through [CB12].

Multiple cells may be simultaneously balanced. It is left to the user’s discretion to determine the ideal number of cells to concurrently balance. Adjacent cells should not be balanced simultaneously. This may cause cell pins to exceed their absolute maximum conditions and is also not recommended for external balancing implementations. Additionally, if internal balancing is used, care should be taken to avoid exceeding package power dissipation ratings.

The total duty cycle devoted to balancing is approximately 70% per 250 ms. This is because a portion of the 250 ms is allotted for normal cell voltage measurements through the ADC.

If [ADC_EN] =1, OV and UV protections are not affected by cell balancing, since the cell balancing is temporarily suspended for a small slice of time every 250 ms during which the cell voltage readings are taken. This ensures that the OV and UV protections do not accidentally trigger, or miss an actual OV/UV condition on the cells while balancing is enabled.