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TMS320F28377D-EP: Power-up sequence - VDDA turn-on

Josef Rypar47
Prodigy 240 points

Part Number: TMS320F28377D-EP
Other Parts Discussed in Thread: TMS320F28335

Hello,

I'd like to ask about requirement to "power VDDA together with VDDIO".In our previous design based on TMS320F28335 we supplied the the the VDDAIO and VDDA2 pins from standalone, clean 3V3 source (with separate ground AGND) that was turned on when the 1.9V (VDD) was good.

We're now transitioning to TMS320F28337 where the power-on sequence requires to ramp up the VDDA together with VDDIO which is not easily achievable with our current topology (i.e. to make the VDDA supply tracking the VDDIO supply).

I expect that this requirement is based on assumption that the VDDA is derived from VDDIO through LC filter, as it is done on the evaluation board.

Is it really mandatory to guarantee the simultaneous ramp up of VDDA and VDDIO or is there any time period for which it is tolerable to delay the turn-on of the VDDA (after the VDDIO is good)?

Thank you.

Josef Rypar

  • 0
    TI__Guru 62930 points

    Josef,

    I am researching this requirement and will post back here.

    Regards,

    Wade

  • 0 in reply to Wade Vonbergen
    TI__Guru 62930 points

    Josef,

    I have been working with the mass market team to understand the history and requirements.

    Here is response to the requirements.

    Our test and qualification is performed with the 3.3V supplies within 0.3V of each other, we do not perform any extensive evaluation of devices when one 3.3V supply is powered and the other unpowered.  Since we do not have test data for an asymmetrically powered condition we have added this conservative requirement to guide users away from an extreme case of asymmetrically powered supplies for extended durations.  We have no reason to believe a brief supply ramp asymmetry between the 3.3V supplies will cause failures.  To state differently: extended duration (DC) separation of VDDIO and VDDA beyond 0.3V is the primary motivation for this requirement, however we cannot provide definitive guidance for intermediate durations as this will depend on the duration of supply ramp separation and number of power cycles.  Anecdotally, this is a common supply topology and we have not found reports of any issues for products which ramp these supplies independently.

    If this answers your question, please click "This Resolved My Issue"
    Regards,
    Wade