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BQ25792: Solar panel charging

M Anand
Prodigy 240 points
Part Number: BQ25792
Other Parts Discussed in Thread: BQ25798

Hi,

We have a 12V PV panel + 4s LFP battery charging application using the BQ25792.

Ideally, we'd like to use BQ25798, but there are some supply issues with that part, and as a temporary stopgap measure we're trying to the use BQ25792.

I am aware that the poor source qualification method differs between the two parts, with 25792 latching off after some retries, whereas the 25798 does not.

My question is if that poor source latch-off only happen at POR as indicated in Section 9.3.4 of the datasheet or at any time when the PV source is unable to supply the Ipoorsrc current, as would happen at night.

In other words: given the following scenario:

1) it is daytime, all is well, load is being supplied by the panel and battery is charging;

2) night falls, the PV panel gradually loses any ability to supply any current and the charger goes into supplement mode, supplying the VSYS load from battery;

3) sun comes up

Should we expect the charger to automatically start supplying the load/charging when the PV panel is able to supply sufficient current, or would the charger have gone into HIZ and would need host intervention to clear EN_HIZ.

I have also seen in response to a similar question on the forum that the VINDPM setting would play a role in preventing automatic charge resumption, rather than the poor source latch-off, but it is not clear what that might be.

Appreciate any insights.

Thanks for your help,

Best regards,

Anand.

  • 0
    TI__Guru**** 165886 points

    Hi Anand,

    Regarding 2, VINDPM is the feedback loop that regulates the charger's input voltage to a fixed voltage in order to prevent it from pulling too much current from its power source (essentially maximum power point regulation). The issue is that 792's VINDPM does not automatically reset (which 798 automatically does if MPPT is enabled) as the voltage drops due to reducing sunlight.  

    Regarding 3, the issue will be poor source latch into HiZ due to too little sunlight.

    As long as the battery voltage hasn't fallen below your host's minimum voltage, the host software can reset VINDPM (for example after using the ADC to read the input voltage) and/or HiZ (restart poor source) as needed.

    Regards,
    Jeff

  • +1 in reply to Jeff F
    Prodigy 240 points

    OK, understood, thank you, Jeff.

    Best regards,

    Anand.