TMS320F280049: How to config F280049 run at 100MHZ with internal oscilator

Hi Jack,

If you are using internal oscillator to configure PLL to output SYSCLK, you will have to account for +/-3% temperature variation. Hence the example above uses IMULT to account for worst case +/3% variation (i.e. considering internal oscillator is running at 10.3MHz). 

Their is no limitation to configure IMULT=20, you can do it but if the INTOSC is running at 10.3MHz, it will configure SYSCLK =103MHz, which may have non-deterministic results as the max device frequency is 100Mhz.

Regards,

Nirav 

Hi Nirav,

Thanks for this info.

If the max device frequency are not allowed to above 100Mhz, that would be dangerous even though using external oscillator due to varitions.

If the worst case is 9.7MHZ in some of the device, then the CPU CLK = 9.7MHZ*19.25/2 = 93.3625MHZ according to the manual recommendation. It will slow down CPU speed perfromance, how to resolve this situation if I want the CPU works at 100Mhz? 

And I see that some of the solution code(tidm_1000) still config the IMULT = 20 while using internal ocsilator, why?

Hi Jack,

Their is margin built on top of 100MHz for any kind of clock jitter, so device can run beyond 100MHz. But design does not have extra +3% on top of the margin built in to accommodate INTOSC drift across temperature, hence TI recommends configuring PLL at 97MHz if using internal oscillator as the clock source. 

External crystal variation should be very very low less than 0.1%, which is built in design margin. Please go through the Crystal requirement section in Data sheet.

If you need CPU to run at 100MHz TI recommends using External Crystal and not internal oscillator. Like I mentioned earlier, their is nothing preventing you to run CPU at 100Mhz using INTOSC, but when you run it across temperature, INTOSC may have +3% drift which may increase the CPU frequency beyond built in margin.

TIDM is just demonstrating the configuration of device to 100MHz, TI recommends reviewing the data manual for actual configuration. Though I will take a note and follow up with our Systems team to get that corrected.

Regards,

Nirav