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Original question:

TPS65919-Q1: to adjust power-up / down sequence

TPS65919-Q1: to adjust power-up / down sequence

Hayashi
Expert 1840 points
Part Number: TPS65919-Q1

Hi teams.

Would you tell ne the follow question?

The pass condenser and sequence
Is this device affect capacitance of pass condenser if this is to be rampdowned?
If the TDA3x is light load, I think the device will not keep the sequence.
Best regards.
Hayashi
  • 0
    TI__Genius 10000 points
    Hi,

    The recommended capacitance values are listed in the datasheet. We have validated that the power up sequence works under light loads (even no load) with these capacitor values.

    Does this answer your questions?

    Thanks,
    Nastasha
  • 0 in reply to Nastasha
    Expert 1840 points
    Nastasha san

    Thank you for your reply.
    If the capacitance of the decoupling is large, I want to know if there is a problem with the sequence.
    The datasheet of TDA3x is written in "vdd must ramp down after or concurrently with vdd_dspeve".

    I think if the TDA3x is low load, this condition does not keep. Because if the time constant of CR is low load, this will be spend long time for ramp down.

    Is there any difference in the above contents?
    If there is problem, is there any way?

    Best regards
    Hayashi
  • 0 in reply to Hayashi
    TI__Genius 10000 points
    Hayashi-san,

    I think there is no issue if they are ramped down at the same time.

    Have you seen our user guide for TPS65919/TDA3x? www.ti.com/.../slvuas4d.pdf

    This document may assist you with your design. We have tested this solution in the user guide and had no problems with the capacitance disturbing the sequencing.

    Thanks,
    Nastasha
  • 0 in reply to Nastasha
    TI__Genius 10000 points
    Hayashi-san,

    Just to clarify - there is no issue at light loads because TPS65919 has active discharge. The LDOx have 30 - 125 ohms discharge resistance, and the SMPSx have 9 - 22 ohms discharge resistance. (In datasheet)

    Thanks,
    Nastasha
  • 0 in reply to Nastasha
    Expert 1840 points

    Nastasha san

    Thank you for your reply.

    I know, the outputs of the TPS65919 have a discharge resistor.

    I think the ramp down  of follow User's Guide (7.2 ACT2OFF Sequences) is affect from decoupling capacitance.

    Please let me know  if this understanding is wrong.

    Best regards.

    Hayashi

  • 0 in reply to Hayashi
    Expert 1840 points
    Nastasha san

    In other words, when the TDA 3x is light load, I want to know if the decoupling capacitor of the TPS 65919 has the possibility that the ramp down slows and deviates from the sequence.

    Although it is said that it is equipped with a discharge resistance, please check the above contents.

    Best regard.
    Hayashi
  • 0 in reply to Hayashi
    TI__Genius 10000 points

    Hayashi-san,

    This is the data we took at no load. While it takes time to discharge, the sequence is still in the proper order. Additionally, the rails have discharged enough before the next rails begin ramping down. It is okay if the rail is not at 0V before the next rails turn off since it remains low. We have no concern here.

    Thanks,

    Nastasha