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BQ25172:ISET resistance value of BQ25172

YUTAKA ISHIHARA
Prodigy 20 points
Part Number: BQ25172

Tool/software:

ISET resistance value of BQ25172
I set RISET to 750Ω in order to set the charging current to 400mA.
The actual measured value was only 200mA.

Is there a problem?


Battery: NiMH 2 cells

  • 0
    TI__Guru* 75646 points

    Hi Yutaka

    This could be due to thermal regulation (TREG) reducing output current due to high power dissipation.  Check the ISET pin, it should be 1V when devices is in current regulation,  400mA.

    What is input and output voltage when you see 200mA?

  • 0
    Prodigy 20 points

    Hi, Bill.

    I cooled the IC with a cooling spray and confirmed that the current was 400 mA.

    I also confirmed that when the input voltage was lowered from 5 V to 4 V, the current was 400 mA.

    I believe your observation is correct.

    Thank you very much.

  • 0 in reply to YUTAKA ISHIHARA
    TI__Guru* 75646 points

    Hi Yutaka

    Thanks for the update.  Anything that will improve thermal performance of the PCB or reduce power dissipation will help this problem.

    Entering thermal regulation will not stop charging only extend the time due to reduced current, the timer is reduced by half and time is doubled.