Kinetis MicrocontrollersのトピックRe: KV44 flexPWM with frequency dithering and nano edge

KV44 flexPWM with frequency dithering and nano edge

katha — Thu, 09 Sep 2021 15:53:38 GMT

Hello everybody,

to realize a spread spectrum frequency modulation with two pwm signals and nano edge placement I currently vary the periode using VAL1. Frequency varies between 105kHz - 95kHz, nanoedge 2x clock runs at 168MHz.

I realized, that the periode setting with VAL1 seems to be non linear. Also the dutycycle values doesn't seem to vary linear. If I use SDK function PWM_UpdatePwmDutycycle() the dutycycle does not come out exactly.

Could you explain why the values are non linear?
Do you have a better idea how to realize a frequency dithering feature?

Many thanks

Katharina

Re: KV44 flexPWM with frequency dithering and nano edge

diego_charles — Wed, 15 Sep 2021 22:49:24 GMT

Hi @katha

I hope you are doing well!

Could you detail us further the non-linear variations that you are seeing for the duty cycle and PWM period? For example , when you call PWM_UpdatePwmDutycycle() to increment/decrease/set the duty cycle , the error in the duty cycle edges can vary in many different clock cycles?

Our colleague Xiangjun Ron provides a document and demo code introducing the Nano-edge placement. To get fine edge control the period the FRACVAL registers are also used. Nano-edge placement feature for eFlexPWM module based on KV4x

According to the KV44, the fine edge control , can be also simulated with dithering, this applies for those sub-modules that are not supported by the Nano edge placer.

All the best

Diego.

Re: KV44 flexPWM with frequency dithering and nano edge

katha — Thu, 23 Sep 2021 06:38:54 GMT

Hie Diego,

got it working, dithering function does not work for a frequency dithering from 95kHz to 100kHz, just around the nearest whole number.

Non linearity was because of rounding problems.

Regards

Re: KV44 flexPWM with frequency dithering and nano edge

diego_charles — Thu, 23 Sep 2021 20:48:23 GMT

Hi @katha

I am glad that you have find out the problem! Thanks for sharing.

Diego.