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BQ25895M doesn't work when Vbus diconnected.

Nicky Lim
Genius 3195 points
Other Parts Discussed in Thread: BQ25895M

Hello,

There is some problem with BQ25895M.

1. Symptom : BQ25895M doesn't work with Battery when Vbus diconnected. It occurs occasionally

2. Test Condition

  1) Booting with Battery (3.6 ~ 4.2V) 

  2) Connect Charging Adapter(Travel Adapter) to Vbus  => Charging status indicated.

  3) Disconnect Travel Adapter from Vbus  => System Power OFF occurred occasionally. (about 3 times/100 times) 

==> At that time PMID / SW / SYS pin out is around  0.2~0.4V and REGN  and  TS is  0V.

Could you let me know why this kind symptom is occurred?

I attached schematic.

Please see attached, and let me get your answer ASAP.

Regards,

Nicky

  • 0
    TI__Guru*** 143870 points
    It appears that the BATFET is turning off. If you toggle /QON pin, does the IC return to normal operation? When the adapter is removed and OTG pin is high, the charger enters OTG mode after a short delay. What is the loading on PMID at this time?
  • 0 in reply to Jeff F
    Genius 3195 points
    Hi Jeff,

    There is no load at this time.
    And she didn't test /QON toggling, but only did BATTFET_DIS bit clear, not set SET_RST bit reset.

    Regards,
    Nicky
  • 0 in reply to Nicky Lim
    TI__Guru*** 143870 points

    Is there additional capacitance on PMID pin, not shown on the schematic?

  • 0 in reply to Jeff F
    Genius 3195 points
    Hi Jeff,

    No, there is not additional capacitance on PMID pin.

    In attached schematic, total 69uF capacitance is connected between BAT pin and GND, beside 10uF recommended in datasheet.
    Can it be the root cause?

    Regards,
    Nicky
  • 0 in reply to Nicky Lim
    TI__Guru*** 143870 points

    69uF is not enough capacitance to cause a current spike large enough to trip BATFET OCP.  I will need to see oscope waveforms when this happens:  VIN, VSYS, VBAT, IBAT. 

  • 0 in reply to Jeff F
    Genius 3195 points
    Hi Jeff,

    I requested those scope data to customer, as soon as I get, I will let you know.

    There is one more question.
    This symptom is occurred during adapter connect - disconnect test repeatedly.
    During that time, can BQ25895M be damaged by ESD?
    And if BQ25895M got ESD, what happens?

    Regards,
    Nicky
  • 0 in reply to Nicky Lim
    TI__Guru*** 143870 points
    How rapidly is the connect/disconnect? The input voltage abs max rating is -0.3V to 20V. I would not expect ESD damage unless there is significant under/over voltage. It is unlikely that ESD damage on VBUS would cause the BATFET to turn off. To confirm, the ICs are functional after the BATFET is turned back on, yes?
  • 0 in reply to Jeff F
    Genius 3195 points
    Hi Jeff,

    To duplicate the symptom, Connect adapter and then disconnect it immediately. and repeat it .

    Yes, after BATFET turned on, IC works well.

    Regards,
    Nicky
  • 0 in reply to Nicky Lim
    Genius 3195 points

    Hi Jeff,

    I attached scope waveform when it happens. but Ibat cannot measured because customer doesn't have Current Probe.

    Test Condition is as below

    1. Vin : 5.2 ~ 5.3V

    2. Vbatt : 3.7 ~ 3.9V (well duplicated)

    3. Load on Vsys : 20 ~ 30mA (well duplicated)

                                   100 ~150mA (seldom duplicated)

    Please see attached Waveform and let me get your opinion.

    Regards,

    Nicky

  • 0 in reply to Nicky Lim
    TI__Guru*** 143870 points
    Are they using a real battery? What is the actual battery voltage? Why does it collapse to 2.4V and they oscillate? I would expect the battery voltage to remain stable. It appears there is a very resistive connection between BAT pin and the battery.