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BQ77915: Fault recovery method without load removal detection

fuji
Prodigy 180 points
Part Number: BQ77915
Other Parts Discussed in Thread: BQ76920, BQ76930, BQ76940

I'd like to use BQ77915 for our product as internal battery protection. After shipment from our factory, load connected to BQ77915 can NOT be removed.
Could you let me know how to disable Load detection as recovery method from UV,OCD,...

In our test, once some fault occured and DSG FET is turned off, we can't turn on the system. 

I'm considering about 2 ideas.

1) Change R_LD and then VLD keeps under VLDT
-> If OCC fault occurs, is it impossible to recover ? If we assume OCC will not occur because OCC threshold(20A) is much higher than charge current (1.5A), 1) is useful solution ?

2) Remove CHG FET and DSG FET. Connect CHG pin and DSG pin to MCU. 
If the MCU detects fault state of BQ77915, then MCU reduces system current or stop charging or etc.

I had seen other questions in E2E and I found BQ7791504. Is it better to use for our product ?

  • 0
    TI__Guru* 80963 points

    Hi,

    The BQ77915 has factory programmable options for recovery and one option is a timer auto-release. Unfortunately, with the orderable options, the part numbers available only have load removal as the recovery option. If the volumes for the project are high enough, we might be able to generate a new part number with the other option programmed.

    The BQ7791504 has current and temperature faults completely disabled. So this device only has over-voltage, under-voltage, and cell balancing. This might be a good option if that fits your application needs.

    A more flexible option is a battery monitor like the BQ76920. (The BQ76930 and BQ76940 are also available for higher cell counts). The BQ76920 has registers so that you can modify the fault thresholds using an MCU.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 180 points

    Hi Matt.

    Thanks your support.

    I have an additional question about the load detection mechanism of BQ77915.

    Our system is connected to PACK+/PACK- and PAKC+ line has FET switch to turn on/off the system.
    When turning off the switch, the leakage current is about 10uA.

    When the leakage current is 10uA, V_LD (10uA x 200kohm(R_LD_INT) = 2V) is larger than V_LDT (1.3V).

    I think this means that BQ77915 can't detect load removal by turnning off the system.
    And if the leakage current is decreased under 5uA (V_LD=1V), BQ77915 can detect load removal.

    These my considerations are correct ?

  • 0 in reply to fuji
    TI__Guru* 80963 points

    That sounds correct, but I think it would be important to test this on an EVM. The 200k resistor value is only a typical value, so I do not know what the expected range will be on this pin. There are no min and max values for this parameter in the datasheet, so I am afraid the distribution could be a problem.

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 180 points

    Hi Matt.

    I tested with BQ779504 and it works well.

    Because current protections of BQ7791504 are disabled, can I remove R_SNS and make short between SRP and SRN ?

  • 0 in reply to fuji
    TI__Guru* 80963 points

    Yes, SRP and SRN can be shorted together for the BQ7791504.

    Regards,

    Matt