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F2808 power sequencing

Mitja Nemec
Genius 5885 points
Other Parts Discussed in Thread: TMS320F2808

 Hi!

 

I am designing a board with F2808. Reading the TI's pdfs it is clear that the only two ways to power the DSP are:

1. to power both rails (3.3 V, 1.8 V) together or

2. ramp 1.8 V rail before 3.3 V rail in order to get glitch free power-up on GPIO pins.

Why do all the solutions (ezDsp schematic, recomendend power soulutions availabile on TI's swebsite) do the oposite - first ramp up 3.3 V rail and then ramp aup 1.8 V rail.

Any comments, experiences are welcome.

Regards, Mitja

  • 0
    TI__Prodigy 640 points

    Mitja,

    Your question has remained unanswered for quite long and by now your PCB might be ready. Anyway let me try my best.

    F281x generation came out before F280x. F281x devices required 3.3V to ramp before 1.8V. Looks Spectrum Digital copied F8212 power design on F2808 eZDSP. It is incorrect, as far as F2808 sequencing is concerned. For the eZdsp board it will not matter as long as nothing is connected to it. But, for a larger system it would cause the problems if some GPIO pins are used to initialize any logic on the board. Since this is a very specific issue, it might not have affected many designs.

    As a CORRECT design, for F280x (and F2801x, F2823x, F2833x) devices 1.8V should ramp before 3.3V.

    Latest reference designs on TI site show the power sequence in a CORRECT manner. For example TMS320F2808 and TMS320F2833x ControlCARD and TMS320F2833x reference design (SPRC541).

    Regards,

    Pradeep Shinde