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TPS65217: TPS65217CRSLR VSYS voltage is no stable.

Faridm
Prodigy 30 points
Part Number: TPS65217

Tool/software:

I am using TPS65217CRSLR for DDR3. Please see my attached schematics.

I am seeing the voltage at  VSYS pin 8 and 7 fluctuating between 5V and 3.3VDC, Please see attached image. R742 is removed meaning that PB_IN is floating. However, I see the voltage at pin 25 is also fluctuating between 5 and 3.3VDC. This fluctuation happens at the same time with VSYS

Yellow signal is VSYS and blue trace is PB_IN signal.

Schematics is below:

Can anyone verify our circuits and tell what might be the cause of this voltage fluctuation. this seems to be the case on all my boards. I doubt it is a bad PMIC. Thank you!

  • 0
    TI__Genius 14620 points

    Hello,

    Thank you for reaching out. The thread has been assigned to the device expert but please expect delay in response by tomorrow as there is holiday in US today. 

    BR,

    Ishtiaque 

  • 0
    TI__Expert 6965 points

    Hello Farid,

    Apologies for the delayed response, 

    The internal source for the PB_IN comes from the source for SYS, so it makes sense that this phenomenon is observed in both pins.

    I want to confirm that it appears you are not using USB or BATTERY, and AC is the main power input for your system, is this correct?

    • If BAT is not being used, please connect a pull down resistor (1k - 10 kOhms) between BAT (pins 4,5,6) and GND.
    • C97 is recommended to be 22 uF

    Are you also able to provide waveform capture of VPMIC (AC Input) to see the stability of the Input source?

    Best Regards, 

    Sarah