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BQ24610 Goes Into Fault

en-US
Prodigy 55 points
Other Parts Discussed in Thread: BQ24610

I'm troubleshooting another engineer's design who is no longer available. Many of the product's having the charging circuit work fine. However, several fault in the range of 30-40mins after charging starts, Stat1 = Stat2 = H (OFF). It doesn't seem to matter whether the battery needs a few hours of charging (where VBat ~ 11.3V) or VBat is closer to 12.56V), at the 30-40min time frame the charger goes into fault. The battery doesn't appear warm. The battery being charged is a 3S1P.

Tcharge = 5.2hrs (Cttc=0.056uf), VBat=12.58V, IChg=1.68A)

I don't really know where to be looking, but this is a common problem exhibited by this product. Suggestions on where to be looking and what to be looking for would be most appreciated.

  • 0
    TI__Genius 11480 points
    Hi,

    So to confirm - Most of the products work fine (all of the time?), and several will fault shortly after charging starts.

    The 30-40 minute time frame is consistent with the pre-charge safety timer. This is set internally to ~30 minutes, with some error. If the battery is not past the "pre-charge" phase (if the voltage of Vfb is less than 1.55 V) when this timer expires, then it will fault. If a timeout fault occurs, the SRN node will source 2 mA as seen in the datasheet.

    You can also check for a short in the battery when this occurs. That will set a fault.

    Input over voltage may also be occuring (ACOV). What are you using for an adapter?

    It sounds like you have already ruled out temperature, but what are you using for your TS pin voltage divider resistors and are you using an NTC thermistor?

    It also sounds like the fast charge timer is not an issue.
  • 0 in reply to David Wiest Jr
    Prodigy 55 points
    David,

    Yes, most of the products work fine -- presumably all the time and several fault during this time frame after charging starts. I just observed that on one of these 'bad' boards, the current VBat = 12.73V while charging. Shouldn't charging have been terminated? The TS resistors are 9.76K to VREF, the other v-divider resistor to ground is 768K, the NTC = 10K. The adapter voltage is 15V and no battery short.

    I'll start to investigate these areas. I had wondered about whether an incorrect valued component had been installed on the bad boards, but have not come up with anything yet.

    Regards,
    Bill
  • 0 in reply to en-US
    Prodigy 55 points
    David,

    I am expecting that Vfb is to remain fairly stable at ~2.1V. On the bad board while the Vbat > 12.58V (the expected voltage), at Vbat = 12.98V, Vfb moved around between 1.926 to 2.095V -- it was never very stable. For some reason on this board the BQ24610 does not terminate charge when the battery is overcharged and just faults at around 30-40 mins.

    Also, I measured Vrsr (across the 0.01 ohm sense resistor) while charging and on a good board Vrsr dropped from Vrsr = 0.0080V to 0.0016V the closer the Vbat got to the expected 12.58V for a 50mV Vbat change. This makes sense that it's decreasing as it approaches the charge termination voltage. On the bad board Vrsr only changed from Vrsr = 0.0014V to 0.0013 while VBat went from 12.328V to 12.431V -- a 103mV change occurred during charging. I'm having difficulty understanding the cause of this behavior.

    Regards,
    Bill
  • 0 in reply to en-US
    TI__Genius 11480 points
    Hi BIll,

    Sorry for the delay. It seems like the charger on the "bad" boards isn't regulating quite right. Would you be able to send me a schematic, and I may be able to help you a bit better? It is definitely worth double checking soldering/component values on the bad boards, as well.