• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 82 subscribers
  • Views 477 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LAUNCHXL-F280049C: SDK dead band

Genatco
Guru 56308 points

Part Number: LAUNCHXL-F280049C
Other Parts Discussed in Thread: DRV8320

Surprised shoot through from voltage transient beginning of Offset adjustment, shorts two NFET.

Lucky the NFET's have 100ns dead time typical but dead delay set 180ns (hal.h) same as for 6 step.

1. Does HAL_setupPWMs() dead band set (true) cause issues for drv8320rs built in dead band or PWM generation?

Seemingly two dead band delay configurations can overlap and do more harm than good cause spurious signals.

2. Does SVPWM require longer dead times than 6 step 20kHz 50µs periods?

3. Does call HAL_setupPWMDACs(),  somehow defeat previous call to HAL_setupPWMs(), revert ePWM generators dead band to disabled state?

      // setup the Dead-Band Generator Control Register (DBCTL)
      EPWM_setDeadBandDelayMode(obj->pwmDACHandle[cnt], EPWM_DB_RED, false);
      EPWM_setDeadBandDelayMode(obj->pwmDACHandle[cnt], EPWM_DB_FED, false);

  • 0
    TI__Guru** 117160 points

    1. No. The final dead time is the maximum setting number between C2000 and DRV8320 if both enable the dead time.

    2. No. SVPWM is independent of dead-time.

    3. No, PWMDAC should use the different ePWM modules with motor control.

  • 0 in reply to Yanming Luo
    Guru 56308 points

    Yanming Luo said:
    1. No. The final dead time is the maximum setting number between C2000 and DRV8320 if both enable the dead time.

    So both devices will add RED/FED delay time to the existing edges, it will double the edge time delay.

    That means 200ns dead time was being set for drv8320rs and seems to explain why shoot through for 180ns. NextFETS have Trr 36ns, why 200ns then? It seems the gate saturation is greater and SVPWM takes longer to ensure switches are indeed off? And the switching looses are greater with SVPWM for a combination of reasons.

    Yanming Luo said:
    2. No. SVPWM is independent of dead-time.

    Oddly SPRUHJ1H trouble shoot guide show >2µs for SVPWM. Cypress SVPWM kit sets dead band 800ns for 10Khz modulation. There seems to be some reason to have longer shut off times for SVPWM that 6 step is not as prone to exhibit. Like to have a scientific evaluation as to why the industry is setting dead time so high for these faster NFETS.

    Yanming Luo said:
    3. No, PWMDAC should use the different ePWM modules with motor control.

    Right I see that but was curios how 180ns dead time caused shoot through 50% duty offset calculation. Increased dead time to 220ns after 1/2 bridge ST but have not yet tested again.