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BQ24179: Charger does not change state when going from poor source to good source

Chris Hahn
Prodigy 55 points
Part Number: BQ24179
Other Parts Discussed in Thread: BQ25798

Hi,

We have designed product using the BQ24179 using a standard USB charger on one port and a solar charger on the 2nd port.  When we use the solar charger the input voltage will drop when the sun is blocked and eventually we will be in a "poor source" state.  Once the sun comes back out again the charger does not move out of this "poor source state" even though the input voltage is high enough.  So the charger is stuck in this "no charging state".  

I have read "8.3.5.2 Poor Source Qualification" and this makes sense why this occurs.  Does TI have a suggestion on how to handle this situation?  I could clear the EN_HIZ bit every 5mins or so to start the qualification cycle again, but I don't like the idea of waking up a system every 5 mins which may already be low on power. Is there a better solution which would at least trigger an interrupt when voltage was high enough so I can start the qualification again?

If polling is the only answer, then would you have a list of recommended alternatives for a charging chip?  We need to have alternatives which are available for a build in the next month or so, so I assume this limits us a little as well.

Thanks for the help,

Chris

  • 0
    TI__Guru**** 170716 points

    Hi Chris,

    Unfortunately, periodic polling by the host to clear HiZ is the best way.  A hardware method would be to periodically pull VBUS below VBUS_UVLO using a series FET switch between the panel and VBUS pin. 

    If you can change to BQ25798 in QFN like hotrod package, it is essentially a BQ24179 with poor source modified to retry indefinitely.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Guru**** 170716 points

    Hi Chris,

    I completely forgot that the ILIM_HIZ pin allows you to force HIZ externally so you could do the same thing as I mentioned above but on that ILIM_HIZ pin.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 55 points

    Thanks Jeff.

    The BQ25798 was the original component we were going to use two months ago, but there was no availability of that part (and still none).  That was our preferred part as well.

    I need some clarification with your hardware method.  You mentioned pulling VBUS below VBUS_UVLO (or toggling ILIM_HIZ) periodically.  That still seems like the host would need to do the toggling.  Or are you imagining something like a 555 timer?  Those timers can chew up a lot of battery I think.  

    Thanks for the clarification in case I was misunderstanding.

    Chris

  • 0 in reply to Jeff F
    Prodigy 55 points

    One more clarification about ILIM_HiZ.  The description says:

    "When the pin voltage is below 0.75 V, the buck-boost converter enters non-switching mode with REGN on. When the pin voltage is above 1 V, the converter resumes switching."

    When the pin voltage drops below 0.75V or goes about 1V does this trigger an interrupt?

    Thanks again,

    Chris

  • 0 in reply to Chris Hahn
    TI__Guru**** 170716 points

    Hi Chris,

    For the hardware toggling of ILIM_HIZ, I think it could be as simple as shown below:

    When REGN goes away because poor source has shut down the IC, the PFET turns on which capacitively connects the panel to pull down NFET on ILIM_HIZ pin. When the CR charges, the NFET turns off.  Might need a diode clamp on NFET gate.  Regarding the interrupt, I need to test tomorrow.  I also want to confirm that the pulling the HiZ pin gives the same result as toggling the HiZ bit. It should but, as you pointed out above REGN stays on when ILIM_HIZ is pulled low.

    Changing to BQ25798 is the simplest option.

    Regards,

    Jeff   

  • 0 in reply to Jeff F
    Prodigy 55 points

    Thanks again Jeff.

    The circuit doesn't quite make sense though.  This is because REGN is used as the source of the voltage divider for ILIM_HiZ.  ILIM_HiZ will already be low in a Poor Source state.  This means the NFET drain won't change voltage

    p.108 datasheet:

    I must be missing something here in the sequence of events.

    As another note, our solar panel can vary from about 3V to 8V.  So it sounds like I need to use a voltage divider to get an appropriate voltage at Vpanel in your picture.

    Chris

  • 0 in reply to Chris Hahn
    TI__Guru**** 170716 points

    Hi Chris,

    You are correct.  I tested on the bench and REGN collapses.  So, the only way to reset from poor source is to remove and replace VBUS or use host to toggle HiZ bit.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 55 points

    Thanks for the clarification Jeff.  Not quite the answer I was hoping for, but I'll go ahead and say the issue is resolved since it's a limitation of the IC.

    Thanks again for your investigation.  It was very helpful.

    Chris