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Original question:

BQ24092: Fluctuating charge current

BQ24092: Follow up question

Robert Whalley
Prodigy 200 points
Part Number: BQ24092
Other Parts Discussed in Thread: BQ24090,

Could you explain in more detail the following sentence from the related post's response?

"This could trigger near the CC / CV point with right resistance between battery and OUT pin"

In particular the significance of the resistance between the battery and the OUT pin.

Many thanks.

  • 0
    TI__Guru 67866 points

    Hello
    I reviewed the original post and your below comment is significant.
    "Disconnecting the TS pin completely stops this behavior."

    My guess is when you disconnect the TS pin / NTC you add a 10k resistor to ground to keep the unit operating.
    The BQ24092 will change charge voltage and current near hot and cold termination points see figure 17 in data sheet. This is JEITA profile, note the BQ24090 does not have this.
    Check the voltage on TS pin when the problem is occurring.
    Normal charge is 790mV to 278mV.
    Between 278mV and 178mV the charge voltage is reduced.
    Between 790mV and 1230mV the charge current is reduced.
    See page 9 of data sheet V-TS 0C, V-TS 10C, V-TS 45C and V-TS 60C.

  • 0 in reply to Bill Johns
    Prodigy 200 points

    Hi,

    To clarify - when I disconnect TS it is left floating, therefore, as I understand it, forcing TTDM mode and disabling TS monitoring. Does that change your answer?

    I will definitely check the voltage on the TS pin when the problem happens as you suggest.

    Many thanks,

    Rob Whalley

  • 0 in reply to Robert Whalley
    TI__Guru 67866 points
    Hi
    No does not change answer or area that we should look at.
  • 0 in reply to Bill Johns
    Prodigy 200 points
    I have measured the voltage on the TS whilst the charge current is fluctuating by about 50mA, in pulses that are 30ms wide, and it is 0.435V. That seems to be in the middle of the normal range. What is that telling us?
  • 0 in reply to Robert Whalley
    TI__Guru 67866 points
    Voltage look about right for the NTC. In TTDM mode works OK and in this mode the device does not terminate charge.
    Try connecting the TS pin to ground with a 10k resistor.
    This will rule on misbehavior of the battery pack NTC.

    Do you have a scope capture of the voltage at OUT vs Current at OUT pin?
    Can you send schematic of circuit?
  • 0 in reply to Bill Johns
    Prodigy 200 points
    I'll pull the TS pin down with 10K as you suggest, and I'm happy to send a schematic of the circuit, but not on this forum because it is confidential. If you could advise how to send it to you directly, that would be great.
  • 0 in reply to Robert Whalley
    TI__Guru 67866 points
    We are working this problem using conversation feature of Forum off-line and will close post.