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BQ2003: Can't start new Charge Cycle while in top-off mode

Larry Fey
Prodigy 40 points
Part Number: BQ2003

We are having difficulty starting a new charge cycle while in top-off mode by toggling the CCMD pin with a 1ms pulse.

Is there any reason that this should not work?

Datasheet says that this should start a new charge cycle.  Item 3 under heading Starting A Charge Cycle.

We are charging from a USB plug source.  If we disconnect and reconnect the USB when in top-off mode, a new charge cycle begins.

  • 0
    TI__Genius 10240 points

    Larry,

    What was the status of the CHG pin before and after the CCMD pulse. Top-off is part of a charging cycle, and the battery is close to be fully charged. Can you explain what's the goal of a new charging cycle at this condition?

  • 0 in reply to ezhao
    Prodigy 40 points

    The CHG pin is in the 50% duty cycle state when we are issuing the CCMD pulse.

    Our problem is that the fast charge cycle is inconsistent on when it stops charging the battery and goes into top-off.  Sometimes the battery gets fully charged, and other times it stops for a reason we can't explain.  It does not look like the delta voltage is causing it, and it also does not look like a temperature change either.  It stops well before the time out setting.  So our thought was to measure the battery after the fast charge cycle in firmware, and if it has more capacity that could be charged, issue a charge command pulse to start the fast charge cycle again to keep this going.

    We have been trying to do some testing to figure out what is triggering the stop of the fast charge cycle, so we could possibly address this issue that way.  But in the mean time we thought we could also add this control to our firmware to be another solution.

  • 0 in reply to Larry Fey
    Prodigy 40 points
    Do you have any further assistance you can provide for this issue?
  • 0 in reply to Larry Fey
    TI__Genius 10240 points
    Larry,

    BQ2003 is a legacy part released around 20 years ago. The datasheet states the falling or ring edge edge on CCMD can start a new charging cycle but it seems not very clear whether the slew rate matters. Can you also try different slew rates? In parallel, we will get an EVM in 2-3 days so we can check on the bench as well.
  • 0 in reply to ezhao
    Prodigy 40 points
    We have been able to start new charge cycles, if we change the mode from TM1=HIGH, TM2=FLOAT (C/2 with Top-Off) to TM1=FLOAT, TM2=LOW (C/2 no Top-Off).
    I have been trying to determine why the bq2003 is sometimes terminating the fast charge cycle early.

    The CCMD line is controlled via a microcontroller turning on/off a 2n7002 MOSFET. This means that the fall time of the signal is very fast, and the rise time is set by the pull-up resistor (10K and the FET and pin capacitance). But since we are able to start a new sequence when we disable the top-off, I don't believe that this is a signal ramp speed issue. I think that it has to be completely done with a charge cycle (which includes top-off mode if enabled) before it will allow the state to change to a new start charge cycle.

    Any way to determine which factor is causing the end of the fast-charge cycle?
  • 0 in reply to Larry Fey
    TI__Genius 10240 points
    Larry,

    From our end, we checked on the EVM and the safety & hold-off time for a fast-charge rate of 1C and 4C with top-off enabled held true. We did not encounter any early fast-charge termination.

    You mentioned that the fast charge cycle is inconsistent and we think this is likely triggered by the reasons of voltage. Are you measuring the battery voltage from the battery itself? Or are you measuring near the BAT Pin Voltage? The voltage measured at the battery terminal might be below the reading on your BAT Pin due to the cable connection. Please refer to the data sheet Section “negative delta voltage termination” for possible impact. Please make short cable low impedance connection from the battery to the charger, as the cable creates voltage difference between the battery and BAT pin.