SLUUCJ0 November 2023 BQ76907
The BQ76907 integrates Cell Overvoltage Protection (COV), monitoring the voltage of every cell using the voltage ADC data, and triggering a COV alert or fault when a cell voltage exceeds the COV threshold. The COV threshold is programmable from 0.0 V to 5.5 V in 1 mV steps and is set by the Protections:Cell Voltage:Cell Overvoltage Protection Threshold configuration register. The COV protection is enabled using the Settings:Protection:Enabled Protections A:[COV] configuration bit.
The COV circuitry triggers an alert signal when an overvoltage event is first detected, then triggers a fault after the voltage is measured above 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 Overvoltage 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 above the COV threshold during a SLEEP mode measurement, the device returns to NORMAL mode and continues taking measurements at a more frequent rate until the COV alert has cleared or a COV fault has triggered. The timing of COV delay can be different while cell balancing is active, depending on settings described in Chapter 10.
When a COV fault is triggered, it recovers if the maximum cell voltage drops below the COV threshold by a COV_HYS hysteresis level, which is programmable as 50 mV, 100 mV, or 200 mV, or autonomous recovery can be disabled. The COV_HYS hysteresis level is set by the Protections:Cell Voltage:Cell Overvoltage 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 COV fault is triggered, the device turns off the CHG FET if configured for autonomous FET control based on setting in Settings:Protection:CHG FET Protections A[COV] (the DSG FET remains enabled if already enabled). The device recovers (if configured for autonomous FET control) based on all cell voltages being below COV threshold – COV_HYS.
| Status | Condition | Action |
|---|---|---|
| Normal | Max cell voltage ≤ Protections:COV:Threshold | Safety Alert A()[COV] = 0 |
| Alert | Max cell voltage > Protections:COV:Threshold | Safety Alert A()[COV] = 1 |
| Trip | Max cell voltage > Protections:COV:Threshold for Protections:COV:Delay duration |
Safety Alert A()[COV] = 0 Safety Status A()[COV] = 1 and CHG FET can be disabled depending on settings |
| Recovery | Safety Status A()[COV] = 1 and Max cell voltage ≤ Protections:COV:Threshold - Protections:COV:Recovery Hysteresis |
Safety Status A()[COV] = 0 and CHG FET can be re-enabled based on settings |