topic KV4x FlexPWM: Unwanted Initial HIGH Pulse on PWMB After Restart with Polarity Change in Kinetis Microcontrollers

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

EmbedALM — Fri, 25 Jul 2025 10:11:31 GMT

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?

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

Celeste_Liu — Wed, 30 Jul 2025 04:31:54 GMT

Hello @EmbedALM ,

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

BRs,

Celeste

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

EmbedALM — Wed, 27 Aug 2025 05:16:25 GMT

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

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

EmbedALM — Fri, 29 Aug 2025 05:02:03 GMT

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

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

Celeste_Liu — Fri, 29 Aug 2025 06:18:39 GMT

Hello @EmbedALM ,

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

BRs,

Celeste

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

EmbedALM — Thu, 11 Sep 2025 05:49:52 GMT

under driver example..PWM

topic KV4x FlexPWM: Unwanted Initial HIGH Pulse on PWMB After Restart with Polarity Change in Kinetis Microcontrollers

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

My Goal:

My Configuration:

Observed Behavior (with Scope Images Attached):

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

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

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

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

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