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Original question:

BQ76940: Have this part pass the certification UL/IEC/EN60730

BQ76940: major safety relevant faults that can not be prevented with bq76940 when used as single chip

swathi venugopal
Prodigy 20 points
Part Number: BQ76940
Other Parts Discussed in Thread: BQ77905, BQ7718

This is from the previous thread -The bq76940 is not designed with full internal redundancy itself that would ensure its robustness for safety as a single-chip system, so the customer system will generally need additional method (such as the secondary protector) to ensure safe operation.

What can i additionally achieve with secondary protector ? what are the major safety relevant faults that can not be prevented with bq76940 alone .

  • 0
    TI__Expert 5090 points
    Hi Swathi,

    You will generally consider the possibility that any component in your system may fail during operation, and this includes the bq76940. For example, you are presumably using the device's integrated protection features because they are needed for your system. You include a CHG FET and enable the OV protection in the bq76940 to disable the FET if the cell voltage exceeds an allowable threshold. If the CHG FET failed as a short circuit, how could you stop the battery from being charged? Or if the bq76940 internal circuitry failed such that the control to its CHG pin was unable to deassert the pin, then the CHG FET would stay on indefinitely.

    Similarly, if the DSG FET failed as a short, you could not stop an excessive discharge or short circuit, which could lead to overheating and thermal runaway of the battery. Or similarly if the bq76940 internal circuitry failed such that the control to its DSG pin was unable to deassert the pin, then the DSG FET would stay on indefinitely.

    What else is needed will really depend on how your system is configured, what else in your system may provide additional protection that would still ensure safety if there was a failure in one component. If your battery pack is embedded and not designed to be removed by the user, then you may have additional circuitry between a charger input voltage that could provide further protection even if the CHG FET was shorted or on indefinitely. Or if you include a secondary OVP protector (such as bq7718), it can detect an overvoltage condition on the battery due to overcharging and blow a fuse, even if the CHG FET cannot stop the charging. If you also need redundant protection against an excessive or short circuit discharge current, or an overtemperature condition, you can consider including bq77905, which can control a separate set of series protection FETs.

    Thanks,

    Terry