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TMS320F2812: Power Up Sequence

Robin Stahel
Prodigy 10 points
Part Number: TMS320F2812


Hello

I'm using the TMS320F2812PGFA in one of my projects. Now I found out, that the Power-Up Sequence ist not correct. 

As shown in the datasheet, the 1.9V supply should not reach 0.3V until the 3.3V supply has reached 2.5V.

In my measurements i found out, that the 1.9V supply is a little bit too early, but not before the 3.3V.

Do i have to change this although the system is runnuing for several years without any problemes with the DSP?

What are the risks if i don't change the power up sequence?

Kind regards

R. Stahel

PS: here's my measurement

  • 0
    TI__Guru* 95315 points

    The primary goal of the power-up sequence is to make sure that the Flash is in a known state during power-up. If the Flash charge pump (powered by VDD3VFL) is active and the Flash is not in reset, you could potentially accidentally program/erase the Flash during VDD power-up. Power sequencing allows a low level on the -XRS pin to properly propagate through to the internal Flash reset signal during power-up. 

    When powering up the 3.3V supply, the I/O pins cannot generate a valid input signal until the supply has reached at least ~2.5V. This means that the reset input (-XRS), even though it is held low externally, may actually be at a high level on the logic side (inside the chip). Therefore, the 1.8V core supply must be held below 0.3V until the I/Os (especially reset) can generate a valid logic level. As stated before, our primary concern is to keep the charge pump circuits (that are used to program the flash) in a reset state during power up to prevent any accidental corruption of the flash memory. It is unlikely that a short reset glitch on the flash pump during power up will corrupt the flash. However this is difficult to prove and hence the guideline in the datasheet. Note that this risk (minimal, but not zero) exists only when you power up. If your product is an "always-on" application, your risk is very minimal.