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Original question:

TPS65218D0: the CPU startup time was proportional to the time when the power was turned on

TPS65218D0: Conditions which DCDC4 stops

R.Fukunaga
Expert 2505 points
Part Number: TPS65218D0
Other Parts Discussed in Thread: AM4378

Tool/software:

Hi all,

I asked in a related thread before.

The output of DCDC4 drops at the timing of the red line in the attached file, and I confirmed that it does not start normally and seems to repeat the startup sequence.

The output starts to drop about 2.5 ms after DCDC4 output is ON.

In the situation, after 5 ms of DCDC4 rising up, the internal PG DCDC4 is judged as NG and the startup seems to fail.

Could you tell me all the conditions under which DCDC4 output goes OFF?
Do you know the cause?

Best Regards,

Ryusuke

  • 0
    TI__Expert 6245 points

    Hi Ryusuke,

    I am replying to the thread as device expert Sarah is out until 5/20. She will get back when she is back in office.

  • 0
    TI__Genius 10107 points

    Hi Ryusuke,

    Thank you for your patience.

    Are you able to provide more details so I can better understand what may be the cause of this issue,
    Is this the same schematic as the previous thread?
    If not, could you please share most recent schematic files to my email, or through private message?

    It may also help to share waveform captures of DCDC4 and PGOOD, and DCDC4 and DCDC3 or 1.

    Thank you.
    Best Regards, 

    Sarah Lao

  • 0 in reply to Sarah Lao
    Expert 2505 points

    Hi Sarah,

    I'm Sorry to have kept you waiting.

    Yes. The circuit diagram is the same as the previous thread.

    I send you a waveform capture as follows.

    If you notice anything, please comment.

    Best Regards,

    Ryusuke

  • 0 in reply to R.Fukunaga
    TI__Genius 10107 points

    Hi Ryusuke, 

    Thank you for the waveform capture. It appears DCDC4 is not able to reach the targeted output level 3.3 V. 

    May I know the total capacitance on this rail , including that near the AM4378 processor?

    In the layout, are these capacitors (C21, C22, C23) placed close to the DCDC4 pin?

     
    And what is the expected current draw for this rail?

    It may be that the DCDC4 is starting up too slowly and causing a timeout error upon startup.
    If startup takes longer than 5ms, the rail will fail to turn on and reset the PMIC. 

    Best Regards, 
    Sarah