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BQ25792: Some issue need to support

user5883945
Expert 1816 points
Part Number: BQ25792
Other Parts Discussed in Thread: BQ25798

Tool/software:

Dears,

   There are some issue need to support;

1. When using OTG to power the load, after connecting the input end to a 12V adapter, the OTG mode cannot be exited; customer needs to plug in an external adapter, IC exits OTG mode, system and charging are provided by adapter；

2. Remove the battery during the charging process,

When the Vbat register displays 9V, it can be charged normally after connecting the battery;

When the Vbat register shows 15V, after connecting the battery, the IBAT displays 0, but the charging indicator LED shows charging, the charging mode register also shows fast charging status, and the values of other registers are also normal without a Fault；

3. What should be the voltage of Vbat and Vsys after removing the battery；

  • 0
    TI__Guru**** 166336 points

    HI,

    Regarding 1, the charger has no way to know if an adapter providing the same voltage or lower as OTG voltage has been attached.  I suggest either using a mechanical switch to sense adapter attach or perhaps host software to modulate VOTG and monitor for voltage movement.

    Regarding 2, I suspect your IC is damaged due to SYS/BAT/BATP pin ringing above their 20-V rating at hotplug. With 4S applications, we strongly recommended (see datasheet app diagram notes) adding a TVS diode to protect the 20V rated BAT, BATP and SYS pins from being damaged at battery plug in.  

    Regarding 3, after battery removal and assuming an NTC fault due to missing thermistor, V(SYS) = MINSYS=12V and battery floats to about 2.xV.  If charge is enabled and no TS fault, BAT and SYS will overshoot above VREG, then the converter turns off for 30ms, causing BAT and SYS to fall to zero if there is a light load on SYS.  I recommend changing to pin2pin and reg2reg BQ25798 to prevent the shutdown at battery removal.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Expert 1816 points

    Hi,

    Customer add the ACFET1 and RBFET1, but still can not exit OTG  and power from adapter when adapter is plug. test the VAC1 ACDRV1 voltage, found that the ACFET1 and RBFET1 is always turn on whether the adapter is plugged in or not.

    without adapter and in OTG mode 

    VAC1 10.82V      ACDRV 16.35V

    adapter plug

    VAC1  12.47V    ACDRV  17.99V

  • 0 in reply to user5883945
    TI__Guru**** 166336 points

    Hi,

    The charger does not auto exit OTG at adapter plug in if the adapter voltage.  As noted above, the charger cannot distinguish between the adapter power and its own converter power at the VBUS node.  The charger's VBUS may become overcharged, causing an OTG_OVP fault, in the fault registers if the adapter is higher than the OTG voltage or if the adapter cannot sink current and the charger is running in PWM mode.  

    Regards,

    Jeff