TMS320F280039C: What happens if DAC ramps down to zero?

Wayne Huang

Genius 15645 points

Part Number: TMS320F280039C

Tool/software:

Hi champs,

I am asking this for our customer.

From TRM spruiw9c (https://www.ti.com/lit/pdf/spruiw9), see below red box.

The user uses DACH ramp generator to trip a EPWM to low.

When the DACH ramps down to zero and if CMPINxP is a little bit lower than 0x0 because of minus comparator input offset, which means there is likely no COMPHSTS=1,

1) Will the DACH still be recharged to RAMPMAXREFS "right after" it becomes 0x0? Or the DACH will not be recharged until EPWMSYNCPER (at EPWM counter=0)?

2) What happens when there is no COMPHSTS=1? Does that mean the PWM output can be 100% duty because there is no trip event?

3 months ago

0 Hadi Moradisizkoohi 3 months ago

TI__Expert 7100 points

Hi Wayne,

Sorry for delay. I will get back to you asap.

Regards,

Hadi

0 Hadi Moradisizkoohi 3 months ago

TI__Expert 7100 points

Hi Wayne,

1) if the output goes high (COMPHSTS=1), then the DACH still be reset to RAMPMAXREFS "right after" that event.

2) Yes, if there is no trip, the ePWM can go to 100% duty cycle.

Regards,

Hadi

0 Wayne Huang 3 months ago in reply to Hadi Moradisizkoohi

TI__Genius 15645 points

Hi Hadi,

For 1), I meant if there is negative offset so that there is no COMPHSTS=1, will DACH still be recharged to RAMPMAXREFS?

+1 Hadi Moradisizkoohi 3 months ago in reply to Wayne Huang

TI__Expert 7100 points

Hi Wayne,

DACH will be loaded with RAMMAXREFS when there is either COMHSTS or EPWMSYNCPER. So, if there is no COMPHSTS=1, the DACH doesn't go to max value RAMMAXREFS.

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TMS320F280039C: What happens if DAC ramps down to zero?