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BQ24140 - General Behavior

Tal Ben Porath
Intellectual 480 points
Other Parts Discussed in Thread: BQ24140, BQ25606, BQ24250

Iv'e been reading the datasheet of BQ24140 (http://www.ti.com/lit/ds/symlink/bq24140.pdf, and there are a few issues which are not entirely clear to me:

1. What happens if both VBUS and VIN are connected to power and "CE" bit indicates on "active" in both?

2. How exactly does the "15min timer" work? If the device is connected to power and I2C communication only starts after more than 15min, will the device respond properly?

3. How exactly does the "32s watchdog" work? When is the dog kicked? 

4. If both  "CE" bits indicate "inactive", is there a possibility we'll enter a "deadlock" situation, in which the battery runs out and device will not allow any charging ever?

Thanks in advance!

Tal

  • 0
    TI__Guru**** 165886 points
    Hi Tal,

    Regarding 1, When two power supplies are detected in default mode, the bq24140 will default to VIN operation and the VBUS
    input will go to high impedance.

    Regarding 2, during the 15 min mode, the charger functions with default settings (VBATREG=3.54V, ICHARGE at low setting). After 15 min, the charger goes high impedance and awaits an I2C write to restart.

    Regarding 3, in 32s mode, the charger is expected a write to the watchdog bit(s) at least every 32s. If not received, the charger's register revert to 15 min mode default settings.

    Regarding 4, yes. If the host doesn't communicate within 15 minutes of power up, the IC enters HiZ mode and will shut down.
  • 0 in reply to Jeff F
    Intellectual 480 points

    Hey Jeff,

    Thank you for this answer and my apologies for my delayed response.

    Regarding 3: do I understand you correctly that in order to charge in any configuration which is not default, we must communicate with the charger every 32s? Is there no way to make the charging settings stable for longer duration (i.e to disable this watchdog or extend its period)? ?If not, it would mean our MCU will have to wake-up every 30s, which is obviously very bad for us.

    Thanks,

    Tal

  • 0 in reply to Tal Ben Porath
    TI__Guru**** 165886 points
    Tal,

    Unfortunately, that is the case. There is no way to disable the watchdog timer.
  • 0 in reply to Jeff F
    Intellectual 480 points
    Hey Jeff,

    Thank you for this (sad) clarification.

    Last (desperate) followup - is there any way to change the default destination voltage from 3.54V?

    In any case - I would suggest in future devices you'd consider providing more flexibility with this feature.
    Also, I think the spec should state this fact more clearly (not only the technical details but the fact that charging above 3.54V requires constant communication).
  • 0 in reply to Tal Ben Porath
    TI__Guru**** 165886 points

    Tal,

    Unfortunately, no.  The default VBATREG is fixed at 3.54V.  This feature and the watchdog were safety features which were considered necessary back when LiIon batteries were first being used in cell phones.  Listed below are some standalone single chargers that do not have these extreme safety features:

    bq25606 - can operate as either a battery charger or OTG back to input, not both at same time.

    bq24250 - battery charger only

     

  • 0 in reply to Jeff F
    TI__Guru**** 165886 points
    If you can give me some details about your end application, I might be able to better recommend the right circuit for you.