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Original question:

BQ25570: is it possible to get 3.3v output from BQ25570 Vout? even battery voltage is Less than 3v?

BQ25570: Vout

M liu
Intellectual 320 points
Part Number: BQ25570
Other Parts Discussed in Thread: BQ25505

Hi, we are evaluating the bq25570 for IoT app. We need 3v3V at the Vout, what is the min VSTOR needs to be at full load (110ma) ? Thanks,

  • 0
    TI__Guru*** 143990 points

    HI M,

    If VOUT = 3.3V then VSTOR should be 200mV higher or 3.5V.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 320 points

    Thanks Jeff. in our application, there will be solar to the VIN_DC. a battery to the VBAT. wanted to know how the bq25570 operates. During the day, the solar charges the battery. The "load" will draw the current 24 hours a day.  If the solar does not provide enough current even if the VBAT is configured to provide 4.2V as charging voltage. Will VSTOR sag when there is not enough light, will the battery provide the current to the load at that point. Second question, we may need an external buck-boost regulator, would TPS6310 + bq25505 (or 25504) a good combination ? Thanks again

  • 0 in reply to M liu
    TI__Guru*** 143990 points

    Hi M,

    If you input power goes away, VSTOR stays connected to VBAT through the internal PFET until the battery discharges down to 2.0V.  The buck boost regulator should work but is not as efficient as the BQ25570/s buck converter and will discharge the battery quickly.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 320 points

    Hi Jeff, can you suggest a high efficiency buck-boost regulator ? which bq do you suggest 25505 or 25504 ? Thanks again

  • 0 in reply to M liu
    TI__Guru*** 143990 points

    Hi M,

    The BQ255xx family members have the same boost charging circuit.  I was comparing the TPS631xx efficiency at light load to BQ255xx's efficiency, although the TPS632xx next generation buck-boost charger likely has slightly higher efficiency than TPS631xx.

    Regards,

    Jeff