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BQ25121: I2C works only if "IN" pin is used but not with BATTERY pin

Hueseyin Demir
Prodigy 40 points
Part Number: BQ25121

1) We are using BQ5100YFPR with PMIC BQ25120YFF and the I2C communication/configuration doesn't work if we just use the Battery input for supplying the IC. 

2) During the WCH I get some Faults which I could not assign to any possible cause (UV, OV, OL).

the Registers are as below: 

C1-0F-AF-60-0E-78-B2-FC-68-0A-00-42

3)If I switch during WCH to battery mode the PMIC config stays valid but the I2C communication doesnt work anymore.

  • 0
    TI__Guru**** 165866 points
    Hueseyin,

    I am sorry you are having trouble. Unfortunately, our BQ25121 support team is out until early next week for the US holiday. Hopefully, you wait until then.
  • 0 in reply to Jeff F
    TI__Genius 12485 points
    Hello, On battery only mode, the /CD pin will have to be high to access I2C registers. Regards, Gautham
  • 0 in reply to Gautham
    Prodigy 40 points

    "CD" high or low makes no difference I cant configure the PMIC over I2C. Its only possible if I supply PMIC over "IN" (WirelessCharging Input, 5V).

  • 0 in reply to Hueseyin Demir
    TI__Genius 12485 points

    Hueseyin,

    That is not expected. We might have to start looking at the schematic. Can you also confirm a few bullets below?

    1. I2C is pulled up to VSYS

    2. EN_HIZ bit is not written

    3. What register are you trying to read? Are you getting NACKS?

    4. Can you drive /CD H-L-H and re read the I2C registers?

    regards,

    Gautham

  • 0 in reply to Gautham
    Prodigy 40 points

    Hi Gautham,

    1) I2C is pulled up to VSYS (2.2V) all the time (only battery mode / Wireless charging mode).

    2) EN_HZ bit is "0".

    3) I try to read all registers.I get NACKS when I go to battery mode or start in battery mode. It is not possible to configure the PMIC.

    4) I have jumpers, so I can change CD to High/Low during runtime. I get only NACKs in Batt-Mode.

    Our HW expert just told me he has already reviewed the schematics with you a couple months ago. So I will contact you via Email to discuss this further.

  • 0 in reply to Hueseyin Demir
    TI__Genius 12485 points

    Hueseyin,

    Thanks for the schematic. I noticed on your schematic that the /CD net is tied to "SYS" where as the rest of the schematic is tied to "VSYS" netlabel.

    Can you have the 5V present and then do a register scan? The settings you sent is still showing /CD pin low. (Register 0x00, Bit B1)

    What is generating the "SYS" rail?

    regards,

    Gautham

  • 0 in reply to Gautham
    Prodigy 40 points

    Hi Gautham,

    thanks for your support. The problem was the /CD pin and unfortunately VSYS!=SYS. Our HW guy will investigate the SYS rail. The I2C comm is working now! (->Six eyes principle:)

    Another thing what I want to understand is the battery charging:

    - So I have to pull the /CD low to be able to charge the battery (WCH+Battery), but Register 0x00 still shows 0xC1 which is a Faultstate: SW is enabled.

    Have you any guess, what the problem is?