TMS320F28335 PWM duty cycle variation

Alex,

I assume that you can create PWM3's waveform correctly and that the main problem is getting PWM3's duty cycle to update at the correct time. 

What I would recommend is creating an interrupt several cycles prior to the moment that you want the duty cycle to update.

For example, if PWM1 is configured to have a PRD of 15000 and configured in up-count mode, I would generate an interrupt at  around 14000 using PWM1's CMPA or CMPB events (assuming they are unused).

In the interrupt, I'd then update the duty cycle.  Make sure PWM3's set to update via shadow-mode so that the update won't happen before you want it to. 

If the problem is synchronization, I'd recommend looking at the Epwm User Guide for your device and then particularly look at the application-specific PWM configuration examples section.  This should help to give you some ideas.


Thank you,
Brett

Hi Brett , thank you very much for the reply. I am not familiar with using c2000, but I did follow some application examples. 

Here is how I configure PWM3. The interrupt you mentioned in the reply should change the value of "RATE_C". Can you give me a specific code example of generating interrupt based on PWM1's CMPA?

void InitEPwm3Example(void)
{

// Setup TBCLK
EPwm3Regs.TBCTL.bit.CTRMODE = TB_COUNT_UPDOWN; 
EPwm3Regs.TBPRD = 750; // Set period 10us
EPwm3Regs.TBCTL.bit.PHSEN = TB_DISABLE; // Disable phase loading
EPwm3Regs.TBPHS.half.TBPHS = 0x0000; // Phase is 0
EPwm3Regs.TBCTR = 0x0000; // Clear counter
EPwm3Regs.TBCTL.bit.HSPCLKDIV = TB_DIV1; // Clock ratio to SYSCLKOUT
EPwm3Regs.TBCTL.bit.CLKDIV = TB_DIV1;

// Setup shadow register load on ZERO
EPwm3Regs.CMPCTL.bit.SHDWAMODE = CC_SHADOW;
EPwm3Regs.CMPCTL.bit.SHDWBMODE = CC_SHADOW;
EPwm3Regs.CMPCTL.bit.LOADAMODE = CC_CTR_ZERO;
EPwm3Regs.CMPCTL.bit.LOADBMODE = CC_CTR_ZERO;

// Set Compare values
EPwm3Regs.CMPA.half.CMPA = RATE_C; // Set compare value

// Set Actions
EPwm3Regs.AQCTLA.bit.CAU = AQ_SET; // Set PWM3A on event B, up count
EPwm3Regs.AQCTLA.bit.CBU = AQ_CLEAR; // Clear PWM3A on event B, up count

EPwm3Regs.AQCTLB.bit.ZRO = AQ_TOGGLE; // Toggle EPWM3B on Zero

// Interrupt where we will change the Compare Values
EPwm3Regs.ETSEL.bit.INTSEL = ET_CTR_ZERO; // Select INT on Zero event
EPwm3Regs.ETSEL.bit.INTEN = 1; // Enable INT
EPwm3Regs.ETPS.bit.INTPRD = ET_3RD; // Generate INT on 3rd event

// Start the cout at 0
epwm3_info.EPwmTimerIntCount = 0;
epwm3_info.EPwmRegHandle = &EPwm3Regs;

}

Alex,

I would recommend taking a look at the INTSEL bit within the ETSEL register.  This should allow you to change what PWM event generates an interrupt.

This register is documented within the EPWM User's Guide for you device.  For the F28335, it is here:
http://www.ti.com/lit/sprug04


Thank you,
Brett