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BQ25756: Some design questions about BQ25756...

Peter Tseng
Genius 5930 points
Part Number: BQ25756
Other Parts Discussed in Thread: BQ25750

Hi Team,

I have some questions about the BQ25756, please help to comment.

Thanks.

1. How to set the battery cells? Using the voltage divider for Vfb, right?

2. Could BQ25756 support detecting the battery status, such as battery absence or over-discharge while power supply input?

3. If I only need one direction charing from AC to battery, may I remove Q3 and Q4?

4. Does BQ25756 support the power path function or not? It seems the charging current will share with system loading according to the datasheet circuit!

  • 0
    TI__Mastermind 21200 points

    Hello Peter,

    Thanks for working with us.

    1. That is correct. You use the voltage divider to change the battery charge voltage. You can use VFB_REG to fine tune the voltage as well.

    2. The BQ25756 can't detect those by itself. You'll need an external circuit to detect the battery and over-discharge.

    3. The BQ25756 needs all 4 FETs for the converter to work correctly.

    4. The BQ25756 is a non-power path part. The BQ25750 has the power functionality.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Genius 5930 points

    Hi Sir,

    Can you help to double-check if charger support detects over-discharge battery or not?

    As usual, the charger IC will run in pre-charging mode for the over-discharge battery.

    And I also found the pre-charging spec. in datasheet.

    Thanks,

  • 0 in reply to Peter Tseng
    TI__Mastermind 21200 points

    Hello Peter,

    Can you elaborate on what you mean by your first question? Do you mean a battery that has really low voltage or a battery that discharging a lot of current?

    The BQ25756 has a trickle charge mode. When the battery voltage is below 3V, the charger will charge at a low current.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Genius 5930 points

    Hi Sir,

    Sorry to confuse you.

    What I mean is the over-discharged battery which the battery voltage is lower than normal.

  • 0 in reply to Peter Tseng
    TI__Mastermind 21200 points

    Hello Peter,

    Thanks for the clarification. Yes, the BQ25756 can support that. It's called Trickle Charge mode in the datasheet.

    Let me know if you have anymore questions.

    Best Regards,
    Ethan Galloway