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BQ25628EVM: The question about the BQ25628EVM output without load.

Ryker She
Prodigy 680 points
Part Number: BQ25628EVM
Other Parts Discussed in Thread: BQ25628

Hi

I have two questions about the BQ25628EVM's output without load.

1.The VBAT and VSYS waveform would keep VREGN for 50ms to 60ms when the system switch to charge status in no load. What causes this phenomenon?

2.When a fully charged battery is discharged below VRECHG (default 100mv), the device automatically starts a new charging cycle. After charging terminates. But in below waveform, the device starts a new charging cycle after VBAT fall 500mv. Is this problem normal? Thanks.

Best regards,

Ryker

  • 0
    TI__Mastermind 23655 points

    Hi Ryker, 

    For 1) can you please provide a waveform showing the behavior you are asking about. 

    In regards to question 2) voltage fluctuation on SYS and BAT is expected when no battery is attached. Since no battery is attached VBAT reduces much faster than if a battery is connected, hence there is some delay between VBAT dropping below recharge threshold and a new charge cycle starting when no battery is connected. 

    It is recommended to disabled charge if you plan to use the BQ25628 without a battery. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    TI__Prodigy 680 points

    Hi Garrett,

    The waveform of question 1) is below. The VBAT and VSYS would keep VREGN about 70ms when the system switch to charge status in no load. 

  • +1 in reply to Ryker She
    TI__Mastermind 23655 points

    Hi Ryker, 

    The time when VBAT and VSYS remain relatively steady is due to the charge termination deglitch time. After the ~50 msec deglitch termination occurs, which is why you then observe VBAT reduce because charger is no longer attempting to provide current to BAT pin. 

    The amount of time before VBAT increases again is due to the recharge deglitch time (typ 256 msec). 

    Best Regards,

    Garrett