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BQ25756: When charger is in constant current mode it skips switchings letting the current build and trips the Efuse LM74930QRGERQ1

Don Devlin
Prodigy 10 points
Part Number: BQ25756

Tool/software:

I do not find any stability formula for this and the eval board hints at putting an RC from ICHG to ground. Is there a way to calculate the best RC for my situation?

I would rather the average current reduce than have the peak current spike.

Both ICHG and ILIM_HIZ have a 1.8K with 0.1uF like shown in eval board.

Yellow - ICHG
Blue - Fault_N from Efuse
Purple - SWI of charger
Green - ILIM_HIZ

  • 0
    TI__Mastermind 30915 points

    Hello Don,

    Thanks for working on this. Your RC value should work. I think there may be something else in the circuit that's causing this.

    I've got a few questions to help debug this:

    • What's the charge current, input voltage, and battery voltage here?
    • Is this on the EVM or a custom board? If it's a custom board, can you send me the schematic?
    • Does this issue happen in both buck mode, boost mode, and buck boost mode?

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 10 points

    The charge current is set in HW to 2A with a 24.9K resistance on ICHG
    The input voltage is nominally 5V but can be as low as 4.75V 
    The battery voltage is 3.7 up to fully charged at 4.2V
    Should be in buck mode.
    Custom board, I will have to see how much of the schematic I can release
    I can say the load is in parallel with the battery and can pull current pretty hard intermittently but then the charger should just current limit and let the battery handle it. 

  • 0 in reply to Don Devlin
    TI__Mastermind 30915 points

    Hello Don,

    Thanks for the information here.

    Can you tell me the specifications for the battery charger that your system needs? I think a single cell battery charger might be better suited to your system.

    Best Regards,
    Ethan Galloway