Power sequencing

So, you have VIO, Vmodem and VUSB. What, if any, are the sequence requirements for bringing these up? Can it be in any order? Does VUSB need to be powered at all?

Hi @Tom,

VUSB does not need to be powered. There are also no requirements on the ordering of VIO/VMODEM/VSB as long as they are brought up within a few seconds of one another.

To be even more specific:

  • If VMODEM is brought up first (or they are brought up at the same time), there will never be any confusion.
  • If VIO is brought up first and VMODEM isn’t present when the STM32 turns on the modem, it will try a hard-reset, but will eventually work fine when VMODEM is powered.

In no case will there ever be any hardware damage or other such issue to worry about.


Beauty. This has been a really aggravating issue with some hardware.

To follow up on this question, is there a minimum rise time for either of the power supply lines (VIO or VMODEM)?

I want to use a supercap to handle the current surges on VMODEM, but its voltage will ramp slowly during initial power on.