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BQ25120A: Charge is not enabled in host mode when dead battery is connected and Vin is applied

Kishan Patel1
Prodigy 60 points
Part Number: BQ25120A

Hello,

I have a problem where charge would not turn ON if I try to communicate with the chip through I2C.

Situation:
Dead battery (<3V) is connected. The host processor power is connected to SYS output (buck converter of the chip).

Here/s what happens.

When I plug in the USB, i.e apply a voltage at Vin,
1. It puts the chip into default mode(no host mode), and it starts charging.
2. The Buck converter turns on through Vin supply, and outputs 1.8V (default), and that powers the host processor.
3. Immediately upon power on, host processor sets the CD pin high, communicates to the chip through I2C, that puts the chip into host mode and It stops charging at this point. (here's the problem, I don't understand why It would stop charging here).

Through I2C I make following changes:

- change Buck converter output to 2.8V

- change ICHRG, IPRETERM and ILIM

- Write '1' to HZ_MODE bit, and '0' to CE bit.

Then it pulls the CD pin low again.

Charge is still off.

4. I disconnect the USB, i.e Vin, and now buck converter it powered by battery, and chip goes to high Z mode.
5. I plug in the USB again and it charges normally.

Please help me with this. I would really appreciate it.

Thank you,
Kishan

  • 0
    TI__Genius 12485 points

    Hi Kishan,

    I see what is happening. When the VIN is present, the /CD pin becomes a charge enable/ disable pin only. HiZ and Active BAT are modes only when the VIN is absent. 

    When adapter is present, you don't need to have /CD pin high to communicate with the part as the chip is ready to accept and perform the I2C operations. 

    Also I would not use the HiZ mode bit but rather use the /CD pin to enter HiZ mode. 

    Let us know if that worked. 

    Regards,

    Gautham

  • 0 in reply to Gautham
    Prodigy 60 points
    Thank you Gautham, for the answer and getting back to me quickly. If I don't touch HZ_MODE bit, and keep CD pin low when USB is plugged in, it charges as expected.

    I really appreciate it. Thank you once again.
  • 0 in reply to Kishan Patel1
    TI__Genius 12485 points
    Great! Feel free to open a new thread if you have any questions!

    regards,
    Gautham