AM6548: ePWM chopping frequency

johni yoods

Part Number: AM6548

Hello TI,

We are working on a custom platform based on the TI's AM6548 reference platform TMDX654GP EVM. The software is based upon the latest release from Texas instruments PROCESSOR-SDK-LINUX-AM65X 06_00_00_07.

We have enabled ehrpwm and generated PWM signals on the desired channels.

We have tried to chop the EPWM frequency by make use of EPWM_PCCTL Register (0x0300003C).

When CHPFREQ field value is 0h(no prescale) the chopped frequency is 15.64 Mhz

if the value is 7h(maximum) the chopped frequency is 1.9 Mhz.

1. Is it possible to generate 300khz signal after chopping or what is the minimum frequency could be generated?

2. Is there any way to divide the system clock frequency(FICLK) which is used to generate carrier clock?

Let me know your thoughts on this.

Regards,

Johni.

over 6 years ago

0 Nick Saulnier over 6 years ago

TI__Guru** 107770 points

Hello Johni,

After a first look through the Technical Reference Manual (TRM), PCCTL[CHPFREQ] is the only place I see to reduce the frequency of the chopper.

Could you help me understand your use case better? Why do you need 300kHz instead of 1.9MHz?

Regards,

Nick

0 johni yoods over 6 years ago in reply to Nick Saulnier

Prodigy 175 points

Hi Nick,

For motor control operation I used 300khz frequency with on time of 20hz. To control on time and possible motor rotation with the same signal I thought chopping would be the solution.

Is it possible to reduce the frequency from 1.9Mhz?

Regards,

Johni

0 johni yoods over 6 years ago in reply to johni yoods

Prodigy 175 points

Hello Nick,

I was wondering if you had any updates on this.

0 Nick Saulnier over 5 years ago in reply to johni yoods

TI__Guru** 107770 points

Hello Johni,

I apologize for the delayed response. Future replies will be faster.

I am not clear on what you mean by "300khz frequency with on time of 20hz". Are you talking about a signal with a 20Hz period, where the high portion of the waveform oscillates at 300kHz? Are you talking about generating a single 50msec pulse that oscillates at 300kHz? What kind of motor is this?

Regards,

Nick

0 johni yoods over 5 years ago in reply to Nick Saulnier

Prodigy 175 points

Hello Nick,

Yes, We are trying to generate a signal with a 20Hz period, where the high portion of the waveform oscillates at 300kHz.

We are using a 3 phase BLDC motor(BLY172S-24V-4000).

Regards,

Johni.

0 Nick Saulnier over 5 years ago in reply to johni yoods

TI__Guru** 107770 points

Hello Johni,

Wanted to give a quick update. Working with a couple other engineers to come up with a good solution for this. Apologies for the delays.

Regards,

Nick

0 johni yoods over 5 years ago in reply to Nick Saulnier

Prodigy 175 points

Thankyou for the update Nick.

Please let me know if you find a solution to this.

Regards,

Johni.

0 Nick Saulnier over 5 years ago in reply to johni yoods

TI__Guru** 107770 points

Hello Johni,

EPWM could use software triggered trip events to create your desired waveforms. Set up the PWM to generate 300kHz waveforms. Software writes to EPWM_TZFRC every 0.05 sec generate a trip event to force the PWM waveform low. You would want a deterministic core like the PRU to implement the software writes so that they occurred at your expected interval.

Unfortunately, the AM65x ePWM does not implement the Digital Compare submodule. TI processors that do implement the digital compare submodule in PWM can use a second PWM to generate a blanking signal instead of using software writes.

Regards,

Nick

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AM6548: ePWM chopping frequency