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BQ25798: BQ25798RQMR VSYS pulsing during power off

Agxin Justin xavier
Intellectual 370 points
Part Number: BQ25798

Tool/software:

i am using the above charger IC the battery is not plugged in 

and the VAC1 path is having power .. When this power is removed the vsys output is not turning of smoothly its toggling 3 or 4 times and then going low 

why is this behavior happening .. the I2C is connected to the TPS25750DRJKR cc controller but the CC Controller cannot configure from our eeprom 

because we are using a different eeprom this time 

e2e.ti.com/.../tps25750-cat24c256wi-g-and-cat24c512wi-gt3

  • 0
    TI__Guru**** 166936 points

    Hi justin,

    Can you send a scope plot of VBUS, SYS, SW1 and SW2 when this occurs?  Also can you confirm that /QON isn't toggling?

    Regards,
    Jeff

  • 0 in reply to Jeff F
    Intellectual 370 points

    Hi Jeff ,

    The CC Controller used is TPS25750DRJKR BQ25798RQMR 

    I will try to capture the waveforms today on the unplug behavior But there are few problems after checking this circuit  completely 

    1.system not negotiating for 15V during dead battery power up (no battery power up )

    I need to  get sufficient power from cc controller so during power up through USB-C the system is crashing due to insufficient power now ..

    If second source poe is plugged up front then its negotiating for 15V and able to get power 

    2 .Hot swapping of powers resulting in failure 

     I remember there was some similar issue earlier in old revision in which where we try to power without battery and face some issues similar to this ..

    https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1353754/bq25792evm-bq25792rqm/5162652#5162652

    Now we have changed the chip to  BQ25798RQMR ..

    we have two power sources connected in the setup without battery 

    1st Poe 21 v out from dcdc controlled by VAC 1  ,and 2nd usbc 45 watts to through CC controller controlled by VAC 2 at  BQ25798RQMR  ,no battery is plugged in .If we provide POE 21V first and USB C IF plugged next then its negotiating for 15V after negotiation the path at the output is from POE  and if Poe Is removed its not switching back to usb and usb cc resets and negotiate again with 5V 

    so  with hot unplugging still its not switching  to other power source connected .I am trying to capture waveforms for all this scenarios will  Please let me know if you have any feedbacks 

    thanks and regards

    Agxin  

  • 0 in reply to Agxin Justin xavier
    TI__Mastermind 34676 points

    Hi Agxin, 

    I'm helping out here with Jeff to support on the USB-C/PD side. Do you have a full-system block diagram or schematic you can share with us?

    Thanks and Regards,

    Raymond Lin