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BQ25892: ADC conversion generates inrush current on VBUS in HiZ mode

Brice RUAS DA SILVA
Prodigy 30 points
Part Number: BQ25892

Hello,

VBUS is disturbed (inrush current) when an ADC conversion is requested by I²C (REG02 : 0x9C)  whereas HiZ Mode is enabled.

How can you explain that ?

- Is it due to the VBUS voltage acquisition ? Only the VBAT voltage is necessary, is it possible for the ADC to acquire only VBAT value and not all values (VBUS, TS, VBAT, VSYS, Icharge) ?

- Or is HIZ mode disabled during ADC conversion ?

Here after, find the values of the registers :

REG00 : 0xBF

REG01 : 0xC0

REG02 : 0x1C (9C when ADC conversion is needed to read VBAT voltage)

REG03 : 0x00

REG04 : 0x3F

REG05 : 0xFB

REG06 : 0x5E

REG07 : 0xCB

REG08 : 0x77

REG09 : 0x4C

REG0A : 0x73

REG0B : read only

REG0C : read only

REG0D : 0x8D

REG0E : read only

REG0F : read only

REG10 : read only

Thanks for your help.

Best regards,

Brice

  • 0
    TI__Guru 57611 points

    Brice,

    What are your test conditions such as VBUS, VBAT and test procedure?

    Thanks,

    Ning.

  • 0 in reply to Ning T
    Prodigy 30 points

    Hello Ning,

    Thank you.

    For your understanding, you have to know that there is only one input (2 contacts) on the electronic board. This input is connected to VBUS (to charge the battery) and to the input of an ADC (to acquire an analog signal : main function of the board)

    In charge mode, a power supply is connected to this input and the bq25892 registers are programmed to charge the battery.

    In acquisition mode, a sensor is connected to the input and the bq25892 registers are programmed to be in Hiz mode on VBUS.

    But in acquisition mode, I need to know the state of charge of the battery by reading (by I²C) the battery voltage measured by the ADC of the bq25892.

    When the ADC conversion is launched (REG02 : 0x9C), I can see a glitch in the data acquires by the ADC.

    Can you explain the glitch on VBUS when an ADC conversion occurs whereas the bq25892 is in HiZ mode ?

    Brice.

  • 0 in reply to Brice RUAS DA SILVA
    TI__Guru 57611 points

    Brice,

    We haven't heard about similar behavior before:

    1. Could you please provide the read-back values for all read-only register values? They provide system status and fault conditions if any.

    2. Could you please provide related waveforms on your observations? Please note that the VBUS waveform should be taken at the VBUS pin of the IC or as close as possible to the VBUS pin.

    Thanks,

    Ning.

  • 0 in reply to Ning T
    TI__Guru 57611 points

    Brice,

    We haven’t heard back from you for a while, the thread is considered solved and closed.

    Thanks,

    Ning.