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BQ25798: What charger chips use perturb and disturb MPPT algorithm and not a percentage of Open Circuit Voltage MPPT algorithm?

Kipton Moravec
Expert 1545 points
Part Number: BQ25798
Other Parts Discussed in Thread: BQ25756

Tool/software:

I am charging 4 18650 cells in series (4S). I was looking at the BQ25798 but saw it was using a percentage of Open Circuit Voltage (VOC) algorithm for MPPT and not a perturb and disturb algorithm as described in  the video on this page https://www.ti.com/solution/solar-charge-controller?keyMatch=solar%20mppt&tisearch=universal_search 

How do I find the chargers that use the perturb and disturb algorithm? I had to go to page 34 in the BQ25798 datasheet to find out it did not work that way. The video made it sound like the TI MPPT was a perturb and disturb state machine. It did not say some use it and others do not.

Kip

  • 0
    TI__Guru**** 165986 points

    HI Kip,

    I apologize for the confusion. The most accurate perturb and disturb algorithm's require a microprocessor with memory and software.  Battery chargers have a state machine, not a processor, and no memory (other than I2C registers). Most battery chargers have input voltage regulation (VINDPM) to prevent them from crashing their input source.  This is essentially static MPP operation.  So, some customers have written software to implement their own perturb and disturb using VINDPM to help find the MPP.  Below are some examples that we have posted:

    https://www.ti.com/tool/TIDA-01556

    https://www.ti.com/lit/pdf/sluaai1

    The BQ25756 has a simplified perturb and disturb algorithm as explained on page 30 of https://www.ti.com/lit/ds/symlink/bq25756.pdf.

    Hope this helps.

    Regards,

    Jeff