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BQ25723: Low battery detection for BQ25723 two LiFePO4 cells.

Enrico Gatti
Prodigy 20 points
Part Number: BQ25723

I am using BQ25723 with two LiFePO4 cells, to generate an OTG voltage of 12Vdc, the external voltage of Vbus is + 12Vdc.
In the absence of Vbus, the OTG voltage comes into operation, Reg.0x35 bit4 = 1b.
I have two problems
1) how to avoid excessive battery discharge when the OTG voltage is running ... the host circuit must constantly read the VBAT voltage, (Reg.0x2C) and switch off by deleting EN_OTG (Reg.0x35 bit4)?
Is there an easier way to reveal / read Low Battery?

Thanks

Enrico Gatti

  • +1
    TI__Genius 11385 points

    Hi Enrico,

    I have deleted your other thread as it was a duplicate.

    The problem your described (deeply discharged battery) is not limited to OTG mode. You can turn off OTG mode, but current from battery can still flow to VSYS through the body diode of the BATFET. 

    I would recommend using a battery gauge/protector/monitor to shut off the current path if the battery is discharged too low.

    Thanks and I hope this helps,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory

  • 0 in reply to Pengzhao Zhu
    Prodigy 20 points

    Thanks Peng for the quick reply.
    One last question,
    Can I use the BQ25723 device in OTG mode, supplying a voltage on Vbus example + 11.8Vdc, shared with a + 12.0Vdc power supply?
    To better explain: the external power supply at + 12.0Vdc is the primary voltage on Vbus, in the absence of + 12.0Vdc, the BQ25723 inserts an OTG voltage of 11.8VdC on the Vbus to keep the external devices connected to the Vbus alive.


    Thanks Peng for your help.

    Enrico Gatti

  • +1 in reply to Enrico Gatti
    TI__Genius 11385 points

    Hi Enrico,

    No, not at the same time. VBUS needs to be below Vvbus_convenz for OTG mode.



    Also, it is never a good idea to tie 2 power supply outputs directly together.

    You may need external circuits such as a diode Or-ing IC (but this may make charging implementation a bit more complicated). Or wait until the 12 VDC is gone before enabling OTG.

    Thanks and I hope this helps,

    Peng

    *Please press "This Resolved My Issue" on the thread if my answer is satisfactory