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TMS320F280039C: Multiple PWM Channels Edge/Start Alignment

Chaithanya Nagirimadugu
Prodigy 180 points

Part Number: TMS320F280039C

Hi Team,
We are working on Full Bridge Inverter as shown below and using 4 PWM outputs of TMS320F20039C controller to switch the MOSFETs.
  1. The PWM Frequency varies between 150KHz to 400KHz.
  2. The duty cycle (of all the PWMs) is fixed at 50%.
  3. All PWMs are Center-aligned.
  4. All PWM channels are updated (TBPRD) sequentially for the required frequency for every 20us.
  5. Dead band of 400ns, both rising and falling edges, for all the frequency values.
  6. Our application is to switch the PWMs (ON/OFF) at a time (Q1&Q4 "ON") and (Q2&Q3 "OFF") and vice-versa, as shown below.
NOTE: We are updating the value of TBPRD of all PWMs during run time.
Requirement: The PWM rising/falling edges to be aligned to drive the MOSFETs as shown above
Problem: As we are updating the PWM frequencies during run time for every 20us, we are getting 20ns delay between edges (PWM4A & PWM5B and PWM4B & PWM5A) as shown in the below DSO image.
The code is as follows below:
  • EPWM_setTimeBasePeriod(EPWM4_BASE, TIME_PERIOD_VALUE); 
  • EPWM_setTimeBasePeriod(EPWM5_BASE, TIME_PERIOD_VALUE);
DSO Waveforms are as shown in the below image:
Please suggest the settings to be taken care to get the alignment as required for the application.
Thanks & Regards.
Chaithanya.