ZHCSMR2B December 2020 – December 2021 BQ76942
The BQ76942 device integrates a suite of secondary protection checks on battery operation and status that can trigger a permanent fail (PF) if conditions are considered so serious that the pack should be permanently disabled. The various PF checks can be enabled individually based on configuration settings, along with associated thresholds and delays for most checks. When a permanent fail has occurred, the BQ76942 device can be configured to either simply provide a flag, or to indefinitely disable the protection FETs, or to assert the FUSE pin to permanently disable the pack. The FUSE pin can be used to blow an in-line fuse and also can monitor if a separate secondary protector IC has attempted to blow the fuse.
Since the device stores permanent fail status in RAM, that status would be lost when the device resets. To mitigate this, the device can write permanent fail status to OTP based on configuration setting. OTP programming may be delayed in low-voltage and high-temperature conditions until OTP programming can reliably be accomplished.
Normally, a permanent fail causes the FETs to remain off indefinitely and the fuse may be blown. In that situation, no further action would be taken on further monitoring operations, and charging would no longer be possible. To avoid rapidly draining the battery, the device may be configured to enter DEEPSLEEP mode when a permanent fail occurs. Entrance to DEEPSLEEP mode will still be delayed until after fuse blow and OTP programming are completed, if those options are enabled.
When a permanent fail occurs, the device may be configured to either turn the REG1 and REG2 LDOs off, or to leave them in their present state. Once disabled, they may still be reenabled through command.
The permanent fail checks incorporate a programmable delay, to avoid triggering a PF fault on an intermittent condition or measurement. When the threshold is first detected as being met or exceeded by an enabled PF check, the device will set a PF Alert signal, which can be monitored using commands and can also trigger an interrupt on the ALERT pin.
For more details on the permanent fail checks implemented in the BQ76942, refer to the BQ76942 Technical Reference Manual. The secondary protection features include: