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BQ24278 /CHG LED latched low

Sadry Tavana
Intellectual 320 points
Other Parts Discussed in Thread: BQ24278, BQ25896, BQ24250

Thanks for quick feedback.  I need to come up with a solution (may be SW) as there over 2K boards built.  A few questions

1) VBATREG spec is not clear in BQ24278.  Why 2 values for TA=25?

2) You say Power Cycle the IC.  Does this mean to remove and insert power to IN pin while battery is still connected as long as battery voltage threshold is met?

3) Is there any SW solution to this Like toggling CD or CE?

4) Will the 6 hour timer unlatch the CHG pin when you get into this condition?

5) The condition of VBAT > VBATREG-VRCH is ALWAYS the case when you charge a battery to full, NO?  Meaning that this device ALWAYS gets into this condition.  If yes, wouldn't this device be useless.  Why has this not been documented before.  Seems to me like a fundamental flaw.

I really need a solution ASAP.  Any help is appreciated

  • 0
    TI__Guru**** 153546 points
    Regarding 1, the first entry for normal operation with normal TS (VWARM < VTS < VCOOL). The second is for normal operation over entire temp range. The third is for JEITA WARM (i.e. battery warm) but IC with TA=25C. The fourth is for JEITA warm

    Regarding 2, yes.

    Regarding 3, no.

    Regarding 4, I haven't tested this but it is unlikely.

    Regarding 5, yes, the IC does not stop charge until V(BAT) > VBATREG-VRCH. The IC was designed assuming the battery would be always attached (i.e. never hot plugged) and power would be removed and replaced. All customers that I have supported used it this way and so we never saw this issue with /CHG. The IC safely charges the battery and terminates. Many customers complained about the /CHG indicator not turning back on for recharge cycles (as the IC was designed to do) and added their own charging/not charging indicator with a simple SVS circuit like TPS3803-01 and/or by monitoring the voltage at ISET, which is proportional to charge current, . The reverse boost circuit and /CHG not indicator recharge cycles were the main reasons for making the part NRND.
  • 0 in reply to Jeff F
    TI__Guru**** 153546 points

    Just to confirm, as I mentioned in the original post before I split it, even though /CHG output goes low when a fully charged battery is attached, once the battery self discharges below the recharge threshold, the /CHG indicator self corrects, charges the battery as a first charge cycle, resulting in the /CHG going high when charge completes. The /CHG indicator is only misleading during the time that the battery voltage is > 4.2V-120mV = 4.08V.

  • 0 in reply to Jeff F
    Intellectual 320 points
    Hi Jeff,

    To clarify:

    1) In our product the battery is never removed (not possible) and this problem occurs.

    2) Our customers have reported cases when the CHG signal is continuously asserted even after charging overnight.

    3) To be able to reproduce the condition #2 I have attached a fully charge battery and then applied power to IN pin and can reproduce this problem on demand. I never disconnect and reconnect the battery with power applied to IN pin.

    4) It seems to be the case that if you charge the battery fully in the product (CHG is hi-z) and then try to recharge (with battery never removed) you can get to this condition which is VERY bad.

    5) Also it seems like you can also get into this condition with charging normally and as the battery gets full, yes?


    Can you confirm I am correct on #4 and #5?
  • 0 in reply to Sadry Tavana
    TI__Guru**** 153546 points
    Regarding 4 and 5, infrequently, I have seen the IC's /CHG indicator inaccurately indicate /CHG following charge complete (i.e. the charger correctly terminates and stops charging but /CHG indicator reports charging) without battery removal and replace. In these instances, once the battery discharges below the recharge threshold, the /CHG indicator resets and usually (but not always) works properly as if it is first charge cycle. The root cause is false triggering of the reverse boost protection circuit.
  • 0 in reply to Jeff F
    Intellectual 320 points

    Thanks for clarification and your attention to this.  Two final questions:

    1) Where can I find the ISET voltage vs charge current information

    2) Is there a replacement for BQ24278 with form/fit/function capabilities?

  • 0 in reply to Sadry Tavana
    TI__Guru**** 153546 points
    Regarding 1, while in CC mode (i.e. charge current = max set per ISET pin resistor), V(ISET) = 1.0V. Once you reach CV mode and the current begins to taper, V(ISET) ~= RISET/KISET + 0.020V. When no charge current is flowing, V(ISET) < 10mV.
    Regarding 2, there is no pin to pin replacement. I would recommend looking at bq24250 if charge current <= 2A for standalone operation or bq25896 if you need 3A charge current and have I2C available.