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TPS65218: Power sequence of DCDC4 and DCDC1 of TPS65218

shigehiro tsuda
Mastermind 9490 points
Part Number: TPS65218
Other Parts Discussed in Thread: AM4376

Hi,

Our customer is using TPS65218.
It seems that the time from the start of P3.3 V_D (DCDC4) to the start of DCDC1 is about 4ms
The specification of the following document is written as 2ms.

8 Power-Up and Power-Down Sequence for TPS65218
www.tij.co.jp/.../slvuaa9a.pdf

Is this start timing correct?
For details, refer to the waveform below.

Best Regards,
Shigehiro Tsuda

  • 0
    TI__Expert 4155 points
    Shigehiro,

    Thank you for your question. You are correct that the delay should be 2ms. I am going to look into this and I will get back to you.

    Thanks,
    Nick
  • 0 in reply to Nick Jakse49
    TI__Expert 4155 points

    Shigehiro,

    I think we figured out what is happening here. Since it is taking longer than 2ms for your rail to reach its PGOOD level the device is instead waiting for the previous rail's PGOOD level to be met. Due to de-glitching the next rail can also have a 1mS delay between when PGOOD is met and the next rail powers up.

    Thank you,

    Nick

  • 0 in reply to Nick Jakse49
    Mastermind 9490 points

    Hi Nick,

    Thank you for quick reply.

    I understood that the 2ms timing of the document is correct, it takes 4ms because 3.3V PGOOD takes over 2ms.

    Is there a problem in operation as a device?

    Best Regards,
    Shigehiro Tsuda

  • 0 in reply to shigehiro tsuda
    TI__Expert 4155 points
    Shigehiro,

    This is how the device should operate. The rise time of the rail can depend on various factors, the biggest probably being the size of the BUCK inductor. A smaller inductor might help if this is an issue. I don't think there would be any issue with the device itself that is causing a longer rise time.

    As long as the processor is fine with how long the rail is taking to get to its required voltage everything should be fine. I think the more important thing is that the rails are brought up in the right sequence, not necessarily how long they take to get there.

    Thank you,
    Nick
  • 0 in reply to Nick Jakse49
    Mastermind 9490 points
    Hi Nick,

    Thank you for quick reply.
    It seems that there is no problem because the power supply sequence of AM4376 has no regulation of timing.

    Best Regards,
    Shigehiro Tsuda