KV4x FlexPWM: Unwanted Initial HIGH Pulse on PWMB After Restart with Polarity Change

[EmbedALM]

Hello,

I'm working with the KV4x series MCU (MKV46F128VLH16) and using Flex PWM submodule 0 to generate a complementary signed center-aligned PWM signal using PWMA and PWMB, with deadtime inserted.

My Goal:

• When the PWM timer is stopped, I want both PWMA and PWMB to remain LOW.

• When the PWM is running, I want true complementary behavior with deadtime — meaning PWMA and PWMB must never be HIGH at the same time.

  My Configuration:

  • PWMA is configured as k PWM High True

  • PWMB is initially configured as k PWM Low True so that both outputs are LOW when PWM is stopped.

  • Before starting the PWM timer, I clear the POLB bit (set PWMB to High True) so that it complements PWMA.

  • After stopping, I set POLB again to return PWMB to Low True so both outputs go LOW.

  This setup ensures:

  • Idle state: both outputs LOW

  • Running state: complementary PWM behavior with deadtime

  • Observed Behavior (with Scope Images Attached):

    • Image 1 – First Power-Up:
      On initial power-up, PWM starts cleanly with correct complementary waveforms. Both PWMA and PWMB operate as expected with deadtime — no glitches.

    • Image 2 – After Stopping and Restarting (with POLB toggled):
      When PWM is restarted after a stop (with POLB changed to enable complementarity), PWMB outputs a single, long HIGH pulse (~10 µs) at the very beginning, before returning to correct PWM behavior.

    • Image 3 – Restart Without Changing POLB:
      If I skip changing POLB before restarting the PWM, there is no glitch, but PWMA and PWMB can both stay HIGH at the same time, violating the complementary condition I require.

• Why does PWMB generate a stretched HIGH pulse (~10 µs) after restart, only when POLB is toggled?

[EmbedALM]

This is the Imported SDK Example with some changes in pwm.c.....Board is twrkv46f150m..SDK version is 2.8.0....under driver example..PWM

[Celeste_Liu]

Hello @EmbedALM ,

Thanks for your post. Could you provide the project to me? I will help check it.

BRs,

Celeste

[EmbedALM]

This is the Imported SDK Example with some changes in pwm.c.....Board is twrkv46f150m..SDK version is 2.8.0....under driver example..PWM

[Celeste_Liu]

Hello @EmbedALM ,

Could you please also let me know which demo you are using?

BRs,

Celeste

[EmbedALM]

under driver example..PWM