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External Oscillator speed for F28035 device

Todd Solak
Intellectual 1425 points

Hello,

I received the following question from one of my customers currently evaluating the F28035.  Any help will be appreciaeted!

Thanks,

Todd Solak - TI

-------------------

I have some questions with the TMX320F28035PAG regarding the SYSCLK.

I would like to have an external Oscillator run at 8 MHz, use the PLL to 7 (multiply by 7) so that the internal SYSCLK is 56 MHz.

I need a CAN clock of  8 MHz (16 time quantas @ 500 Kbaud), so the BRP (baud rate prescaler) can be set to 6 (which subsequently divides the SYSCLK by 7) which allows the SYSCLK to be divided by 7 to get the 8 Mhz.   My main question is: can I run CPU at 56 MHz using external clock oscillator of 8 MHz, and the on-board PLL ?

In other words, is there a combination of scaling options and PLL which will provide a 56 MHz SYSCLK?

 

Any help with this is appreciated.

Thansk and Regards

 

  • 0
    TI__Intellectual 2690 points

    Todd,

    As long as the output of the PLL is greater than 50 MHz (i.e. OSCCLK * PLLCR > 50 MHz) , this should be fine.

    To generate a 56 MHz SYSCLKOUT, you can use an 8 MHz oscillator, PLL multiply by 7, and DIVSEL set to divide by 1.

    OR you can use a 16 MHz oscillator, PLL multiply by 7, and DIVSEL set to divide by 2..

    In the same vein, you can use a 14 MHz oscillator multiply by 8 and divide by 2 (or multiply by 4 and divide by 1)...

    -Christine