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BQ25798: PV charging does not always charge

Christian Cortes
Prodigy 30 points
Part Number: BQ25798


Tool/software:

Setup: 

- VBUS is connected to a a solar panel with a Voc = 5.53V and Vmpp = 4.46V 

- i am programming the MPPT register with 

      

    
mppt_control.en_mppt = MPPT_ENABLE;
mppt_control.voc_rate = VOC_RATE_30S;
mppt_control.voc_dly = VOC_DLY_300MS;
mppt_control.voc_pct = VOC_PCT_3;
- VSISMIN is set to 2.5V (the lowest it can be based on the documentation)
Description: 
- If i use my hand to block the solar panel and then and move it away immediately i can see the charging LED that we have on board turn on indicating that we are actively charging. 
- if i walk away from the sun (inside the office/under a covered walkway) and walk into the sun, the charging never begins. But if i cover the panel again with my hand and quickly uncover it, it charges again. not sure what I am missing here. 
thanks, 
  • 0
    TI__Mastermind 35246 points

    Hello Christian,

    Can your provide a register dump when this issue occurs?

    Can you provide your schematic?

    Best Regards,

    Christian.

  • 0 in reply to Christian Moyer
    Prodigy 30 points

    Hello, so seems like i figured out the problem. The chip enters its undervoltage protection state as mentioned in Section 9.3.13.3. The Solar panel does trigger the interrupts when VBUS is detected but since i am in the shade i am under the Vpoorsrc threshold of ~3.3V so the chip stops switching and a backoff time of 7 minutes happens. I left it in the sun for 7 minutes and timed it. after the 7 minute mark the charger does indeed begin to charge again.