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BQ25703A: BQ25703A output of VSYS_6V6_8V4 was not normal.

Victor Ng
Prodigy 60 points
Part Number: BQ25703A
Other Parts Discussed in Thread: CSD17578Q3A

We encountered a problem of BQ25703A during debugging. After the TYPEC_5V was powered, the output of VSYS_6V6_8V4 was not normal.

When testing, it was found that the REGN was sometimes 4V output and sometimes 6V output. What could be the cause?

The test environment are:

l   Only TYPEC_5V powered, BAT_8V does not powered,

l   I2C and other control signals of charger were not connect to MCU.

l   CSD17551Q3QAT was replaced by CSD17578Q3A

  • 0
    TI__Guru 56650 points
    Hello, Victor,

    CSD17578Q3A should be good.
    What is the CELL_BATPRESZ voltage during the start up (from input source available to converter switching)? On the EVM, it gets voltage from a resistor divider which is pulled up to REGN.
    Also, what is the ILIM_HIZ pin voltage? ILIM_HIZ pin can also shut down the converter.

    Please check does the CELL_BATPRESZ voltage and ILIM_HIZ voltage. If you have a waveform, that can help to speed up the debugging.
  • 0 in reply to Wang5577
    Prodigy 60 points

    BQ25703.zipDear Wang Li,

    Please find attached file.

    Best Regards,

    Victor Wu（吴辉）

    victor.wu@wpi-group.com

  • 0 in reply to Victor Ng
    TI__Guru 56650 points
    Victor,

    Waveform looks OK. Let me explain them:
    1. Q5 (BATFET) gate on and off (有时候打开，有时关）: bq25703A has auto wake-up function which provides 128mA current to the battery terminal until Vsrn voltage goes up to Vsys-min voltage level. So, it can wake up a deeply discharged battery without any host command.
    It is on when the Vsrn below Vsys-min.
    It is off because the 128mA charging current brings Vsrn reaches Vsys-min.
    After the battery reaches Vsys-min, the battery should be able to communicate with the host controller. And then, the host controller can setup the correct charging profile.

    2. At light load (inductor current lower than 0.5A), the converter works at PFM. So, the waveform looks good to me.

    BTW, "输入5V两个检测电流电阻通过与锡并联短路" What does "检测电流电阻" mean? Do you mean R7 and R8? R7 and R8 cannot be shorted out.