SLUUCW9 December 2023 BQ76972
When a cell is severely overdischarged, copper deposition can occur, resulting in very high impedance. If this occurs while the pack is in operation, the BQ76972 device typically detects this and disables the pack before cells reach this low voltage (based on a SUV PF). However, if the device is in SHUTDOWN mode for an excessively long time period and the cells become overly discharged, the pack could still wake and enable the FETs if a charger were attached. If the FETs were turned on in this condition, the pack voltage would rise sharply due to the charging current, making the cells appear healthy. The CUDEP Permanent Fail is used to identify this condition and disable the pack. When enabled, this check keeps the FETs disabled at power up from SHUTDOWN mode until each cell voltage is greater than or equal to Permanent Fail:CUDEP:Threshold for Permanent Fail:CUDEP:Delay seconds. If any cell voltage is below Permanent Fail:CUDEP:Threshold for Permanent Fail:CUDEP:Delay seconds, the CUDEP Permanent Fail is triggered. This PF check is enabled by setting the Settings:Permanent Failure:Enabled PF A[CUDEP] and Settings:Manufacturing:Mfg Status Init[PF_EN] configuration bits.