TMS320F28335: Sampling ADC at the middle of PWM cycles

Ashkan Golestani85

Intellectual 775 points

Part Number: TMS320F28335
Other Parts Discussed in Thread: ASH

Hi ,

I've implemented PWM1,PWM3,PWM 5 (20KHz)and generating signals for DC motor.

I'm genereting 40 KHz PWM 6B for positioning detection.

Iam trying to read ADC4,ADC5 and ADC6 at the middle of the each cycle of PWM6B (40KHz), one sample per each peak.

How to config the ADC to meet my requirment ?

In futher step, I'd like to get 3 sample at the middle of each peak ,means 3 sample in high and 3 sample in low level right at the middle of the PWM signal(40KHz).

Thanks in advance for help

Ash

over 6 years ago

0 Nima Eskandari over 6 years ago

TI__Guru 52200 points

Just to clarify your question, you want to have 3 ADC samples during the EPWM OUTPUT=LOW state, equally spaced out. Then 3 ADC samples during the EPWM OUTPUT=HIGH state, equally spaced out?

0 Ashkan Golestani85 over 6 years ago in reply to Nima Eskandari

Intellectual 775 points

Nima,

Step 1-I want to have one sample when is High ,one sample when is LOW right at the center of each peak.

After I finished step 1,I would like to have

Step2 - 3 Samples when is High at the center and 3 samples when is Low at the center.

By the way ,I already developed the code to have a PWM with higher frequency and activate the interrupt with that timer and getting sample on each trigger. Thats what I do currently.

But ,Iam looking for different opinion .

Any idea and how to config that !?

Thanks

Ashkan

0 Ashkan Golestani85 over 6 years ago in reply to Ashkan Golestani85

Intellectual 775 points

Any Answers!!!

0 Nima Eskandari over 6 years ago in reply to Ashkan Golestani85

TI__Guru 52200 points

When you mention when it goes high and when it goes low, are you talking about the EPWM output or the ADC input? You keep mentioning peak, which I'm not sure what you are referring to. Peak, rising edge, or HIGH level? Which one?

I will assume that you mean when the PWM is in the HIGH LEVEL or LOW LEVEL.

This is what you want to do.

CTR=ZERO is middle of LOW level, CTR=PRD is middle of HIGH level, use these events to kick off ADC.

For the other item, use CMPB, CMPC and CMPD, to place more events around CNT=ZERO and CNT=PRD. You will need to impelement the rest of the timings using a timer.

Nima

0 Ashkan Golestani85 over 6 years ago in reply to Nima Eskandari

Intellectual 775 points

Yes ,I was talking about EPWM .

0 Ashkan Golestani85 over 6 years ago in reply to Ashkan Golestani85

Intellectual 775 points

Nima ,

Yes , I used CNT=ZERO and CNT=PRD for center of PWM signal and I used another timer for sampling extras around those points.

Also I use CTRDIR for double check .

Seems like I'm on the right track .

Thanks Agsin

Ash

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TMS320F28335: Sampling ADC at the middle of PWM cycles