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TMS320F28075 Power Sequencing

Kengo Furuya
Expert 7650 points

Hi Champ,

I know F28075 have the recommended power sequencing for VDD and VDDIO when using an external supply. 

When using an external supply to supply VDD, the voltage on VDDIO should be greater than VDD or no less than 0.3 V below VDD at all times. The supplies should ramp to full rail within 10 ms.

But, I think our Control Card does not care above timing sequence between 3V3 and 1V2 on the board. I attached the part of power device of the schematic.

Could you provide the recommend schematic to keep the power sequencing between 3V3 and 1V2?

 

 

Regards,

Furuya

 

  • 0
    TI__Expert 7885 points
    Hello Furuya,

    I have looked at this on the bench when the CC was first released and recall that it did power up within datasheet requirements. I believe both rails powered up at the same rate. Have you captured the VDD_3V3 and VDD_1V2 signals from the CC during power-up on a scope? If so, can you attach that scope capture to this thread?

    Best Regards,
    Adam Dunhoft
  • 0 in reply to Adam Dunhoft
    TI__Expert 7650 points
    Hi Adam,

    I have not measured the actual waveform. Could you provide your scope capture on the bench?

    Regards,
    Furuya
  • 0 in reply to Kengo Furuya
    TI__Expert 7885 points

    Hello Furuya,

    Please see waveform.


    "But, I think our Control Card does not care above timing sequence between 3V3 and 1V2 on the board."  Was this just an assumption or did you actually see something of concern?

    Best Regards,

    Adam Dunhoft

  • 0 in reply to Adam Dunhoft
    TI__Expert 7650 points
    Adam,

    Thank you for your waveform. It is just assumption from customer, not seeing any concern about it. But, their requirement is to provide any recommendation if TI have it. Customer is also thinking the same opinion with you that the control card does not care about the timing sequence for 3V3 and 1V2. It has no problem from your waveform, but I think it was as it happens.

    Regards,
    Furuya
  • 0 in reply to Kengo Furuya
    TI__Expert 7885 points
    Hello Furuya,

    I looked at the CC power-up waveform on the bench again today just to confirm. The CC is meeting DS requirements. I don't have any specific list of components in which I have available for recommendation, but the supply setup used on the CC will work.

    Best Regards,
    Adam Dunhoft