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ISOUSB211: ISUSB211 Power-up sequence on 1.8V and 3.3V

Part Number: ISOUSB211


My customer plans to input VBUS = 3P3v = 3.3V, VCC = V1P8V = 1.8V.  Could you please let us know the limitation of power sequence?

He plans the following power-up/down sequence.

  • Power-UP : 1.8V up -> 3.3V up
  • Power-OFF : 3.3V off -> 1.8V off

1.8V:___| ̄ ̄ ̄ ̄ ̄ ̄ ̄ ̄ ̄ ̄ ̄ ̄ ̄ ̄ ̄ ̄ ̄ ̄|____

3.3V:_______| ̄ ̄ ̄ ̄ ̄ ̄ ̄ ̄ ̄ ̄|________

Does this sequence has any issues?   Please let us know. 

Thanks and best regards,

  • Hi Hattori-san,

    Thanks for reaching out.

    May I know the time duration between 1.8V power-up and 3.3V power-ups and also on the power-downs? It is preferred that both supplies are powered up at the same time but if one of them needs to be before the other then the 3.3V should power-up before the 1.8V, which is opposite from what customer is planning to do. 

    Let me know, thanks.

    Koteshwar Rao

  • Hi Hattori-san,

    I have checked with the design team regarding your question related to power sequencing of VBUS+V3P3V and V1P8V and we confirm that ISOUSB211 doesn't require any specific power sequencing. Either of the pins can be power first and the device will start operating after both pins are supplied. The waveform that you drawn in your post is not a problem for ISOUSB211.

    Let me know if you have any further questions, thanks.

    Koteshwar Rao