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[ BQ24040 ] Issue of CHG Pin Behavior

Kenichiro
Mastermind 9165 points
Other Parts Discussed in Thread: BQ24040

[ BQ24040 ] Issue of CHG Pin Behavior

Hi,

Can you help me to debug the issue of BQ24040? My customer has reported that CHG pin of BQ24040 does not indicate the charging status correctly. See waveform below (sorry, this does not have CHG pin...), According to customer, the first charging was terminated by some reasons, but from after around 25mS, charging resumed again, but CHG pin does not turn on FET.

From these observation, it seems that BQ24040 goes into TTDM mode. However customer also mentioned that this behavior can be seen only Vbat is around 3.8V and bit different from TTDM mode.

Other information I have is, there is a flexible cable in between BQ24040 and battery. The connection is like below.

USB Connector -> BQ24040 ->flexible cable (OUT and GND) -> Battery

This causes the impedance changes between BQ24040 and battery. Do you think this is potential root cause?

At this moment, I don't have enough information and am still working to make sure mote, but it's really appreciated if you can share anything of your ideas.

Thanks,

Ken

  • 0
    TI__Mastermind 20570 points

    It will be helpful if you can provide scope capture that has /CHG from the customer. The wire impedance can definitely cause inaccuate battery voltage sensing, which may cause early charge termination.

    Please see datasheet page 16 for detailed description on /CHG. The CHG signal is active only during the first charge cycle. Exiting TTDM or the OUT voltage falling below VRCH will not activate the CHG signal if it is already in the open-drain (off) state.

    Is the customer test on our EVM? If not, please also provide schematic.