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BQ25798: BQ25798 Charging Issue

jeno.zhang
Expert 2865 points
Part Number: BQ25798
Other Parts Discussed in Thread: BQSTUDIO, USB2ANY, EV2400

Hi，

When BQ25798 is not connected to a lithium battery, a sawtooth wave of around 8.4V, which was originally a normal waveform, exhibits a phenomenon of jumping up and down, similar to working and stopping periodically, and some may have a faster cycle, while others may have a slower cycle. When connected to a lithium battery for charging, some will improve while others will remain in their original state. I don't know what caused this phenomenon, but it doesn't affect charging and communication, it only occurs when there is no load. 20 out of 100 pieces have this type of problem; The schematic and waveform diagrams are as follows:

  • 0
    TI__Guru**** 166106 points

    Hi Jeno,

    With no battery and charge not disabled due to TS fault or CE pin or bit, a sawtooth waveform between BATREG and SYSMIN on SYS pin is expected.  BAT pin can see waveform between 2.5V and BATREG.  If charge is disabled, the sawtooth waveform goes away. 

    The ILIM_HIZ has limited input current to 500mA regardless of what is detected by D+/D-. Is that enough for your load? It appears you are connected to USB-C controller of some time.  What does the charger VBUS pin waveform look like? 

    Can you provide an I2C register dump from the charger using either BQSTUDIO and EV2400 box or TI-CHARGER GUI and USB2ANY box?  The charger has status and fault registers that report the current state and past faults/states.  The fault registers clear after being read so please only read once.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Expert 2865 points

    Hi Jeff，

    Can high chip soldering temperature cause this problem? The welding temperature is 300 degrees, and the time is slightly longer.

    Thanks！

  • 0 in reply to jeno.zhang
    TI__Guru**** 166106 points

    Hi Jeno,

    I have no data on soldering with 300 degree temp.  Please provide the 12C register dump.

    Regards,

    Jeff 

  • 0 in reply to Jeff F
    Expert 2865 points

    hi Jeff，

    The voltage value of the IIC reading register is synchronized with the test waveform.

    Thanks! 

  • 0 in reply to jeno.zhang
    TI__Guru**** 166106 points

    Hi Jeno,

    Ok.  I still need the register dump.

    Regards,

    Jeff