The BQ76907 integrates Cell Undervoltage Protection (CUV), monitoring the voltage of every cell using the voltage ADC data, and triggering a CUV alert or fault when a cell voltage falls below the CUV threshold. The CUV threshold is programmable from 0.0 V to 5.5 V in 1 mV steps and is set by the Protections:Cell Voltage:Cell Undervoltage Protection Threshold configuration register. The CUV protection is enabled using the Settings:Protection:Enabled Protections A:[CUV] configuration bit.

The CUV circuitry triggers an alert signal when an undervoltage event is first detected, then triggers a fault after the voltage is measured below the threshold steadily for a programmable number of measurements (ADSCANs). The number of measurements required before the fault is triggered is set by the Protections:Cell Voltage:Cell Undervoltage Protection Delay configuration register, which ranges from 1 to 255. The time until a fault is triggered is based on the settings for the voltage ADC measurement speeds, which sets the timing for each ADSCAN measurement loop. Note also that during SLEEP mode measurements are only taken every Power:Sleep:Voltage Time interval, but if any cell voltage is detected below the CUV threshold during a SLEEP mode measurement, the device returns to NORMAL mode and continue taking measurements at a more frequent rate until the CUV alert has cleared or a CUV fault has triggered. The timing of CUV delay can be different while cell balancing is active, depending on settings described in Chapter 10.

When a CUV fault is triggered, it recovers if the minimum cell voltage rises above the CUV threshold by a CUV_HYS hysteresis level, which is programmable as 50 mV, 100 mV, or 200 mV, or autonomous recovery can be disabled. The CUV_HYS hysteresis level is set by the Protections:Cell Voltage:Cell Undervoltage Protection Recovery Hysteresis configuration register. If autonomous recovery is disabled, the fault can be recovered manually by the host sending the 0x009B PROT_RECOVERY() subcommand with the [VOLTREC] bit set.

When a CUV fault is triggered, the device turns off the DSG FET if configured for autonomous FET control based on setting in Settings:Protection:DSG FET Protections A[CUV] (the CHG FET remains enabled if already enabled). The device recovers (if configured for autonomous FET control) based on all cell voltages being above CUV threshold + CUV_HYS.