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BQ77915: BQ77915 SCD recover query

Star Xu
Genius 9645 points
Part Number: BQ77915

Hi

The customer design with BQ77915. 

After the battery output load is short-circuited, remove the short circuit immediately. The CHG and DSG are always low. Only when the charger is connected, the CHG and DSG pins return to high.

In addition, if they are left without any load, after a long time BQ7791514 will enter sleep. Only when the charger CHG is connected, DSG will return to the high.

Attached the schematic.

Please help check it.

Thanks

Star

  • 0
    TI__Genius 16010 points

    Hi Star,

    It sounds like the load-based SCD recovery is working as intended. The 14 version is set to only recover from the current protections via load removal/detection.

    Star Xu said:
    In addition, if they are left without any load, after a long time BQ7791514 will enter sleep.

    Could you explain this further? There is no sleep mode on this device, so what is the customer seeing?

    Regards,

    Max Verboncoeur

  • 0 in reply to Maxwell Verboncoeur
    TI__Genius 9645 points

    Hi Max

    Thanks for your reply.

    They‘re not sure if it went into sleep mode, but there was no output when they do the short test and after removing the short circuit, CHG and DSG are still low . Only when they connected the charger the output recover normal.

    Please help check the schematic and give some suggestions.

    Thanks

    Star

  • 0 in reply to Star Xu
    TI__Genius 16010 points

    Hi Star,

    The schematic looks okay.

    Could they measure the voltage at LD when they expect the SCD protection to recover? The device should enable a high impendence pulldown to VSS when the protection is triggered, and once the load is removed, the LD pin should be pulled low.

    (V_LDT = ~1.3V)

    Regards,

    Max Verboncoeur

  • 0 in reply to Maxwell Verboncoeur
    TI__Genius 9645 points

    Hi Max

    Thanks for your reply.

    When the short circuit is removed, VLD is low, and the voltage is 0V when measured with a multimeter. The multimeter is connected to the VSS pin. When the short circuit is not recovered(the output is short-circuited and then removed. But CHG and DSG are low,) the voltage of VLD is 2.7V, and the battery voltage is 10V at this time.

    Another situation is that when the output short circuit does not recover, use the LD pin short to VSS( or use the negative VSS of the chip to short-circuit the GND, CHG, and DSG of the charger to return to high level), CHG and DSG returns to high.

    Thanks

    Star

  • 0 in reply to Star Xu
    TI__Genius 16010 points

    Hi Star,

    When the FETs are turned off, a weak internal pulldown to VSS will be connected to LD. In this case, it will pull to BAT-, but there is a ground reference at PACK-. Is it possible that BAT- and GND are different and causing this voltage at LD?

    Regards,

    Max Verboncoeur