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Original question:

CCS/TMS320F28377S: HRPWM with Deadband on both Outputs

TMS320F28377D: HRPWM Output A and B are Complementary with Deadband

Olga Caudle
Prodigy 30 points
Part Number: TMS320F28377D


Hello,

I am using TI 28377D Delfino to drive FETs for a synchronous buck converter with high switching frequency so that high resolution mode is required. I understand that output B is capable of high resolution on this device but is it possible to generate a high resolution output B that is dependent on high resolution output A with some deadband? Basically, I need to have a high resolution duty cycle control on output A and generate B as active high complementary of A with a fixed deadband. 

  • 0
    TI__Guru 60865 points
    Hi Olga,

    I believe this is possible per:
    e2e.ti.com/.../654568
  • 0 in reply to Devin Cottier
    Prodigy 30 points
    Devin,

    Thank you for the quick reply! The answer in the thread that you referenced confused me and didn't make it clear whether output B can be both dependent on A and in high resolution. I understood that HR is applied after the deadband module so output B can only be in high resolution only if it is independent of A?

    What I have observed with my set up is that output A is operating in high resolution as intended. Output B is set as active high complementary of output A with 10ns deadband and it doesn't move with high precision as output A does, i.e. changing the duty cycle a little bit moves the falling edge of A but doesn't change B at all. I was wondering if I am just missing something in my settings or if output B is not meant to be in high resolution when being dependent on A with deadband.

    Here are my PWM settings:

    EPwm2Regs.TBCTL.bit.PRDLD = TB_IMMEDIATE;
    EPwm2Regs.TBCTL.bit.CTRMODE = 0; // Up
    EPwm2Regs.TBCTL.bit.HSPCLKDIV = TB_DIV1;
    EPwm2Regs.TBCTL.bit.CLKDIV = TB_DIV1;

    EPwm2Regs.TBPRD = 39;
    EPwm2Regs.AQCTLA.bit.ZRO = AQ_SET;
    EPwm2Regs.AQCTLA.bit.CAU = AQ_CLEAR;
    EPwm2Regs.CMPA.bit.CMPA = 0;

    EPwm2Regs.DBCTL.bit.HALFCYCLE = 1;
    EPwm2Regs.DBCTL.bit.OUT_MODE = DB_FULL_ENABLE;
    EPwm2Regs.DBCTL.bit.POLSEL = DB_ACTV_HIC;
    EPwm2Regs.DBFED.bit.DBFED = 2;
    EPwm2Regs.DBRED.bit.DBRED = 2;

    EPwm2Regs.CMPCTL.bit.LOADAMODE = CC_CTR_ZERO;
    EPwm2Regs.CMPCTL.bit.SHDWAMODE = CC_SHADOW;
    EPwm2Regs.HRCNFG.all = 0x0;
    EPwm2Regs.HRCNFG.bit.CTLMODE = HR_CMP;
    EPwm2Regs.HRCNFG.bit.EDGMODE = HR_FEP;
    EPwm2Regs.HRCNFG.bit.HRLOAD = HR_CTR_ZERO;
    EPwm2Regs.HRCNFG.bit.SELOUTB = HR_NORM_B;
    EPwm2Regs.HRCNFG.bit.AUTOCONV = 1;
  • 0 in reply to Olga Caudle
    TI__Guru 60865 points
    Hi Olga,

    Bear with me as the main HRPWM owner is out-of-office.

    Per section "15.2.5 Deadband High Resolution Operation" in the TRM there is a note:

    "Just like the duty cycle restrictions when using HRPWM, the DBRED and DBFED values
    must be greater than 3 to use hi-res deadband."

    I read this as the the deadband values will need to be at least 3 (half-cycles?) for HR deadband to operate, so you may want to try increasing DBFED and DBRED to at least 3.

    I think you also need to enable HR Deadband in
    HRCNFG2.bit.EDGMODEDB = 2; //10: MEP control of falling edge (CMPAHR)
  • 0 in reply to Devin Cottier
    TI__Guru 60865 points
    Hi Olga,

    Any luck with this, or do we need to investigate further?