SLUUCY8 December 2023 BQ77307
The BQ77307 integrates Cell Overvoltage Protection (COV), periodically monitoring the voltage of every cell, 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 detected above the threshold steadily for a programmable number of CHECK intervals. The number of CHECK intervals 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 Power:Configuration:Voltage CHECK Time parameter, which sets the timing for each CHECK voltage evaluation interval.
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 |