High Freq PWM with duty cycle shifting

Paolo Lazzeri

Prodigy 140 points

Other Parts Discussed in Thread: TMS320C6742

dear E2E community,

In our project we are planning to use TMS320C6742 DSP (core frequency 200 Mhz).

i need to build somekind of sine wave signal generator with frequency up to 230 KHz.

i wish to generate it using the High Resolution PWM submodule.

I'd like to have 10 or better 20 samples for period. This means that in the worst case PWM frequency will be 230 KHz * 20 = 4.6 MHz.

So, I need to change the PWM duty cycle every 1/4.6Mhz=0.217 us. Is this time too short to execute the ISR in order modify the duty cycle? It corresponds at only 43 cpu clocks...

If I should lower the PWM frquency, which is the maximum value I could use?

any help would be very appreciated..

Kind Regards,

Paolo

over 11 years ago

0 Senthilkumar Srinivasan over 11 years ago

TI__Mastermind 43660 points

Hello Paolo,

I believe you can generate 4.6 MHz PWM frequency by changing the duty cycle every 0.217us.

Please refer the below example code (not C6742 based code) where EHRPWM is configured to output a shifting duty cycle which is modified via interrupts at the end of each PRD.

http://processors.wiki.ti.com/index.php/C6747_EHRPWM_Example#Project_Contents

Also refer table 6.76 in SPRS587E for eHRPWM specifications.

Regards,

Senthil

0 Paolo Lazzeri over 11 years ago in reply to Senthilkumar Srinivasan

Prodigy 140 points

Hello Senthil,

thank you very much for your quick reply.

At the beginning of september I'll have the TMS320C6748 DSP Development Kit . This kit has a more powerful DSP, but I think I can downclock it to 200 MHz to be in the same conditions of TMS320C6742. Isn't it?

Regards,

Paolo

0 Senthilkumar Srinivasan over 11 years ago in reply to Paolo Lazzeri

TI__Mastermind 43660 points

Hello Paolo,

Though the maximum operating frequency of C6748 device is 456MHz, you can operate it at 200MHz also.

Regards,

Senthil

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High Freq PWM with duty cycle shifting