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BQ24230: VBAT unstable after deep discharge

GaryC
Expert 3095 points
Part Number: BQ24230

We do the deep discharge while one night without adaptor input. We find the VBAT become unstable after I insert the adaptor 5Vdc. The VBAT and IBAT show in below. 

I know the Vlowv is the same as battery cut-off voltage. But the VBAT in the waveform is around 3.44V(min) ~ 4.31V(max), shape as SIN wave. The VBAT is above Vlowv, the charger should be constantly charging the battery. May I learn from you why have this problem? Thanks

BR,

Gary

Battery spec.

  • 0
    TI__Mastermind 27740 points

    Hi Gary, 

    The voltage on a real battery should not change in the manner shown in the waveform. Is the battery voltage (measured at BAT pin) stable before the 5V adapter is connected? 

    Based off current information I am wondering if the battery pack being tested has an internal protection circuit for deep discharge which has been triggered. The VBAT waveform appears to show the battery is not actually connected to the charger IC. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    TI__Expert 3095 points

    Hi Garrett,

    Thanks for your support.

    After over discharge, the battery of the cut off voltage is 3V, and Over discharge release voltage is 3.2V. Currently we can recharge the battery after insert the 5V adaptor. While the recharge, the battery voltage is around 3.1V, after 20s – 30s running, that we can see the ripple around 0.4Vpp. Please refer below picture and schematic. May I learn from you how to solve this problem? Thanks

    CH1: VBAT, after insert the 5V adaptor.

    After runing 20s – 30s, then the VBAT has big ripple.

    Room in ripple.

    SCH:

    BQ24230RGT SCH.pdf

  • 0 in reply to GaryC
    TI__Mastermind 27740 points

    Hi Gary, 

    Upon review of the provided schematic I see neither OUT or BAT pin have the necessary minimum output capacitance of 4.7uF placed close to the IC. Additionally, input path also does not appear to have the recommended capacitance. In requires a minimum of 1 uF capacitor placed close to IC. 

    The lack of recommended output capacitance may be contributing to the observed VBAT ripple behavior. Please advise the customer to make these hardware adjustments and see if it improves the behavior. 

    Finally, one question for the customer. What is the charge current waveform at the time of the observed ripple? I am wondering if device is possibly operating in supplement mode. 

    Best Regards,

    Garrett