Compiler/TM4C1294NCPDT: Is there way to generate jitter clock for PSU for reduced EMI

the answer depends on a lot of other factors, like how the waveform is to be generated, what kind of resolution do you need, ...

typically you do it via a pwm / ccp block. say that you run your clock at 80Mhz and want 8-bit pwm resolution, that leads to an output frequency of 80M/256 = 300Khz, give or take. you can alter the top. if pwm is used, your resolution is limited to 2/256 = 1%, assuming 50% duty cycle. or you can toggle the ccp pins.

other ways are also possible. but you have to figure out first what approach you want to take.

Thank Danny for this, I believe this is what I'm looking for Timer clock to jitter the PSU frequency as to reduce EMI, which spread spectrum. Again I appreciate for this nice work :-).

I'm designing the schematic and layout later on for low EMI solution, one method is having random jitter on 16MHz clock into TM4C would mitigate EMI issue later on. I have not found IC clock device that done that yet, but I used it in the past (9 years ago). The PPL within TM4C would follow the 16MHz jittered clock to 80 or 100MHz so I need to take care not to have too much jitter that might impact USB operation (which I'm concerned about).

I have not tested TM4C for low EMI, I have not seen proof that it is low EMI device which is the reason for this precaution.

R. 

" one method is having random jitter on 16MHz clock into TM4C would mitigate EMI issue later on."

that sounds different from using TM4C to generate a jittery clock OUTPUT.

if you are looking to minimize EMI on clock INPUT, many of the oscillators produce (clipped) sine wave output, for that purpose.

or we totally mis-understood you?

I'm SO glad that this attempt to, "Jitter the 16MHz, Input MCU Clock" has received notice.

Does this not complicate & confound ALL Timing Efforts - throughout all aspects - of poster's MCU?

And - have there not been reports of  "certain" MCUs "Requiring time to Regain PLL "Lock" - when the input frequency is "disturbed?"      What then?     (poster marches quickly/confidently - into the "unknown!")

Generating the (external) Sepic Supply's clock - via changes to an MCU's Timer Values (NOT its PWM (duty-cycle) values) is easy & agreed - "Hopping the MCU's Clock Input" (may) prove a vastly, "Different Story."

Reducing EMI is a noble objective - but ONLY if the "original design objectives" are (somewhat) maintained! (usually a stable - and known - System-Clock Frequency IS required...)

Hello Richard,

richard payne said:

Even though TI claim there no issue with it based on customer however my experience that they would naturally tend keep thier achievement secret under NDA as they not willing to share invested time and money with other.

I don't want to (and can't) speak for TI as a whole, but for our group specifically that is untrue. Our design guidelines are based on the designs for our own hardware boards which have passed through EMI testing including the latest tests from the updated EU standards which are the most stringent to date. We are very open about sharing what precautions you need to take to ensure that our TM4C devices will not cause any customers issues with EMI testing per international standards such as those mandated by CE compliance.

Again if you need proof... purchase one of our EVM's and see for yourself.

Hello Ralph,

I know you to be caring & truthful - surely you, "believe that which you list, here." That said - would not your (and the firm's case) be substantially strengthened - by simply, "Presenting those latest test results" - especially those performed under updated EU standards?

It is (sometimes) possible to, "Just squeak by" such test - and other times - to pass w/"flying colors!" Clearly the publication of such test results would do much to reduce this poster's (and others') concerns.

It should be noted that the MCU - by itself - is never tested - it is the client's "integrated work product" - which expands upon the Eval board - and argues (even more loudly) for the disclosure of those, "Passing EMI Test results."     The listing of the passing, "spectral analysis" provides the "best proof" - does it not?