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BQ25798: Issue in Detecting with Good Power Source

Muralikrishna Konukati
Prodigy 40 points
Part Number: BQ25798


Hi,

I am using BQ25798 Battery Charge controller in one of our design.

1)I have question whether this IC can be used without battery only for buck and boost operation by providing Input source. If this can be used what are the configurations to be changed.

2) We are facing one more issue in terms of functionality for one of the test case mentioned below. 

when battery is fully discharged and cut off the controller went to brown out state and switched off abruptly. During this time we provided Solar input which is connected at VAC1, Solar voltage is 4.3V, during this time battery is not charging and no output voltage at system load. We provided 12V to VAC2 but the Charge is not switching to VAC2. Can anyone help me out to resolve this issue.

Thanks & Regards,

Murali.

.

  • 0
    TI__Guru**** 171106 points

    HI Murali,

    Regarding 1, yes.  It is recommended that charge be disabled using the /CE bit or pin for prolonged use as a dc/dc converter without the battery.

    Regarding 2, the MUX only auto switches to the other source if the first source is no longer considered good (see poor source detection in the datasheet), not simply because the other source is a higher voltage.  Alternatively, the host can force that source off using EN_ACDRx bit.   Also, keep in mind that MPPT must be enabled with the EN_MPPT bit and only functions if V(BAT)>MINSYS.  Since your battery is fully discharged, MPPT will not function.  If you have the 12V applied, I recommend the following:

    Set MINSYS to the lowest possible setting for longest MPPT runtime

    When V(BAT) gets close to MINSYS, use the host to switch to the 12V supply. 

    Regards,

    Jeff 

  • 0 in reply to Jeff F
    Prodigy 40 points

    Hi Jeff,

    Appreciate for your Quick response. Regarding 2nd question, I hope there is some misunderstanding. Let me explain briefly below regarding test case and issue we are facing,

    1) We are using 4 series LiFePO4 cells.

    2) Battery voltage is completely drained off, now host is shut down.

    3) After that VAC1 is supplied from solar, and the voltage is around 4.3V during this time ACFET1 and RBFET1 i.e., ACDRV1 is enabled but during this time buck boost operation is not performed due to insufficient power from solar and there is no SYS voltage and battery Voltage.

    4) Now we supplied 12V at VAC2 a valid source but during this time ACFET2 and RBFET2 i.e., ACDRV2 is disabled even we are having a good source.

    In this case, is there a way to switch the source from VAC1 to VAC2 alternatively without host control?

    As i understand from your previous statement that we should wait until we get good solar power and the battery to be charged approx. to output SYS voltage and host only can switch from VAC1 to VAC2. Is my understanding correct?

    Please go through and let me know if any clarifications.

    Thanks & Regards,

    Murali

  • +1 in reply to Muralikrishna Konukati
    TI__Guru**** 171106 points

    Hi Murali,

    Yes, your understanding is correct. The charger thinks VAC1 has a poor source and so requires a write to disable HiZ mode, disable ACDRV1 and then enable ACDRV2.  The charger auto tries VAC1 again after 10 mins.   Unfortunately, I see no way around this unless the solar panel is attached to VAC2 and the 12V is attached to VAC1 after the initial VAC2 poor source detection.

    Regards,
    Jeff

  • 0 in reply to Jeff F
    Prodigy 40 points

    Hi Jeff,

    Thanks for your support.

    Regards,

    Murali