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BQ25798: BQ25798 turn off and on the charging function repeatedly

Star Xu
Genius 9645 points
Part Number: BQ25798

Hi 

The customer design with BQ25798. When it is blocked or the sunlight is weak, the solar output power becomes smaller because the battery charging current set by the customer is very large, which causes the solar output voltage to be pulled down to the voltage limit point, thus turning off the charging function.

After turning off charging, the solar output recovers after a while and then turning on charging again. However, due to low power and high current, it will be pulled down again and charging is turned off. If you turn it on and off repeatedly in this way, they will hear a whistling sound. Is there any register can prevent BQ25798 from turning on and off repeatedly like this?

Attached the schematic

LP Gataway PAGE01 Charge IC.pdf

Waiting for your reply.

Thanks

Star

  • 0
    TI__Guru**** 150335 points

    Hi Star,

    The noise likely from the charger's ceramic capacitors vibrating as the charge and discharge.  Smaller footprint ceramic capacitors do not vibrate as bad.  Non-ceramic, extremely low ESR capacitors do not vibrate but are expensive.

    The only bit that might help is ICO, which will try to limit input current instead of allowing input voltage to droop.  

    Regards,
    Jeff

  • 0 in reply to Jeff F
    TI__Genius 9645 points

    Hi Jeff

    Thanks for your help.

    The customer tried to start ICO but it was useless.

    It can be determined that when it is blocked or the sunlight is weak, the solar output power becomes smaller, and the battery charging current we set is very large, which causes the solar voltage to be pulled down to the voltage limit point and the charging function is turned off. After turning off the solar energy for a while, it recovered and started charging again, but the power was still very small and it would still be pulled. In this way, it is turned on and off repeatedly, and the frequency of the switch is just within the hearing range.

    Waiting for your reply.

    Thanks

    Star

  • 0 in reply to Star Xu
    TI__Guru**** 150335 points

    Hi Star,

    If changing the ceramic capacitors is not an option, they can try disabling auto VINDPM and set a fixed VINDPM value that is higher than this power level.  The charger will then not start until the panel voltage is higher.  Then they can enabled MPPT with EN_MPPT bit.

    Regards,
    Jeff

  • 0 in reply to Jeff F
    TI__Genius 9645 points

    Hi Jeff

    Thanks for your help.

    When using solar panels for power supply: the battery is fully discharged and the device shuts down; when the sun rises in the morning, the device cannot be turned on, and the solar interface needs to be replugged and powered on again.

    Waiting for your reply.

    Thanks

    Star

  • 0 in reply to Star Xu
    TI__Guru**** 150335 points

    Hi Star,

    When the battery discharges, MPPT function is disabled.  However the charger's standard auto VINDPM will try to find the lowest input voltage for operation.  That voltage must be higher than 3.6V for the charger to function. I expect the charger to turn and off repeatedly until the battery charges high enough.  At that point the host software can enable MPPT function to even better performance.  Also, I recommend setting MINSYS to the lowest possible setting for the system to function. 

    Is this a 1S application?  If not, I recommend configuring for 1S until the charger is up and running and then change to higher cell count.

    I also recommend setting input current limit clamp to lowest setting possible for the system to run.  Then when the host is up, the converter can increase the input current limit for max charge current.

    Regards,

    Jeff