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F281x: Question on power sequencing

Andreas Goergner
Intellectual 1025 points

Dear Champs,

One of my customers is  powering the F281x according to the datasheet recommendations.

However, there is no slew rate statement on the 3.3V rail in the datasheet. On their board it may happen that the 3.3V supply is rising very slow, and it is also possible that the voltage is staying on a certail level in between 0V and 3.3V for an extended time depending on some environment conditions. So far they have not experienced issues with it.

Their question is: Do they have to expect issues long-term? Do we have recommendations for this?

 

Thanks! 

Best regards,

Andreas

  • TI__Expert 8500 points

    Andreas,

    The datasheet does state in the timing diagram (Figure 6-6) that the ramp of VDDIO and the ramp of VDD should not be greater than 10ms. It is impossible for us to test/specify every possible power up scenario, but as far as we know there is no reliability issue with a slow ramp. The biggest reliability risk is when a >2.5v difference between VDDIO and VDD is present. This puts certain gate oxides in the design under stress. The theoretical amount of time is pretty high for that stress to really cause damage though.

    Regards,
    Dave Foley

     

  • in reply to David Foley
    TI__Expert 8500 points

    Just to clarify my first sentence above: we do not specify a ramp rate. What is spec'd is a max delay time from when VDDIO is powered to when VDD is powered.

     

  • in reply to David Foley
    TI__Intellectual 1025 points

    Dave,

    Thank you for the information.

    Do we have information about brown-out scenarios, meaning if an LDO is taking care about the 1.9V rail and the reset signal properly, and the 3.3V rail is breaking down to a certain below 3.14V? Is this a potential issue?

     

    Best regards,

    Andreas

  • in reply to Andreas Goergner
    TI__Expert 8500 points

    Andreas,

    From a spec point of view I have to say that if the 3.3v rail dips below 3.14v we advise the customer to pull a reset. It is difficult for us to really make recommendations outside of our operating conditions because we are limited to what we can characterize, so we characterize what we guarantee. It is not likely that the device will fall apart when the VDDIO voltage is slightly below 3.14v, but I cannot recommend anything that goes against our datasheet specs. Sorry.

    Regards,
    Dave Foley