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BQ77PL900: When discharge P ch FET short-circuited failure.

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Prodigy 10 points
Part Number: BQ77PL900
Other Parts Discussed in Thread: BQ76942

Hi!

This is a question about the discharge function of the bq77PL900. (SLUS844B–JUNE 2008–REVISED JANUARY 2009,  Figure 1. Stand-Alone Mode )

Even if discharge is not intended, if the Pch FET controlling discharge is short-circuited, current may flow to the load via the parasitic diode of the Pch FET controlling charge.

Especially if the current to the load is not at the level to blow the fuse, I think the current will continue to flow.

While the current value can be monitored by the resistance of the sense resistor, if the Pch FET for discharge fails, it seems there is no means to stop the current. However, is there a way to stop the current in such cases?

Thanks!

  • +1
    TI__Genius 16730 points

    Hi,

    In this case, a connected MCU would need to detect that the FET is controlled to be off and also detect that there is still a discharge current and then blow a fuse.

    You may be interested in the bq76942. This device is from our newer generation of battery monitors and has the functionality to detect that the DSG FET is supposed to be off and that there is a discharge current flowing and drive a pin high to blow a fuse, all on its own. If you're interested, this is explained in more detail in Section 5.3.10 of the device's TRM (link).

    Regards,

    Max Verboncoeur

  • +1 in reply to Maxwell Verboncoeur
    Prodigy 10 points

    We will consider bq76942 for our new machine. Thank you very much for your help.