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Flash integrity on 28335

Simon Haworth
Prodigy 130 points

Hi,

I've just been looking at the documentation which supports the 2833x Flash API, and there is a cautionary note regarding flash integrity, which says "... the device should always be programmed at the fastest possible CPU frequency.  For example if the CLKIN frequency is 30 MHz, program the device at 150 MHz rather than 30 MHz or 60 MHz."

Does anyone have any information regarding the kind of tradeoffs which would be made by not programming at 150MHz?  For example, does this reduce the number of erase \ programming cycles which can be undertaken, or reduce the reliability of the flash even if it's only programmed once at a lower frequency?

In our application, we don't have a fast enough input clock to scale up to 150MHz, but I don't have enough information to know whether I should panic or not!

Thanks in advance,

Simon

  • 0
    TI__Guru 61235 points

    Simon,

    Don't panic.  The faster clock gives better granularity on how long a charge is applied to each flash cell.  The flash algorithms have a specific amount of time they want to apply the flash charge.  So, faster clock lets them get as close as possible to that specific amount.  Hitting this amount of time on the head just gives a slightly "Harder" programming.  In other words, the charge on the cell will be a little bit higher, and take a smidgen longer to decay out over the life of the device (since flash is like a battery.  Eventually, it will discharge and the flash will be left as all 1's.  This takes years and years.  The faster clock speed at programming probably buys some extra fractional percentage of lifetime.  I don't know really.  TI has never quantified the effect.  We just put the note in the API documentation since you may as well do the best you can do with the clock you have on your board.  Since you have some clock, set the PLL to the highest possible setting that doesn't exceed the device rating.  If you can't hit 150 MHz (for a 150 MHz device), hit the highest you can less than that.

    Again, this is nothing to worry about.

    Regards,

    David

  • 0 in reply to David M. Alter
    Prodigy 130 points

    David,

    Thanks for the quick reply - exactly what I wanted to hear, it's not really a problem!

    Regards,

    Simon