PWM Duty Cycle

[jayakrishnans]

Hello

I am using PWM Module in MC56F8037 Microcontroller to generate PWM Signals for MOSFET Control application in my

project. When Iam using the Complementary PWM Setting, the PWM Signal Duty Cycles are getting reduced with increase

in frequency of PWM Module Setting. The Dead Time and Signal Shape is Ok.

eg, a 1KHz PWM and 60% Duty Cycle Setting for first PWM pin generates 60% and 40% Complementary PWM Signals for

1st and 2nd Pins with Correct Dead Time. But for Higher Frequencies like 10KHz, 100KHz, 200KHz etc the Duty Cycles get reduced to about 55-50%

and 35-30% Respectively. I have checked the code in codewarrior, i did not find any error.

is this the hardware problem or have I missed something while changing the Frequency of Operation of PWM Module?

My application requires PWM Signals at 100KHz-200KHz. Please send some suggestions.

Thanks

JK

[xiangjun_rong]

Hi, Jk,

Regarding your issue, I think the "dead time" insertion leads to the issue. Because the dead time is an absolute value which represents the Prescaler*IP_BUS clock, the Prescaler is defined in PRSC bits in PWM_CTRL register. When the PWM signal frequency is low, the PWM cycle time is large, the "Dead Time" insertion effect is not obvious, but when the PWM signal frequency is high, the PWM signal cycle time becomes small, the "Dead Timer" effect is obvious, note that the Dead Time is an absolute time value, which does not vary with the PWM signal cycle time if you keep the PWM_DTMx register intact.

For test, pls set the Dead Timer as ZERO, then test.

BR

XiangJun Rong

[jayakrishnans]

Hi Xiang

You were right, after I adjusted the Dead-Time Register DTIM0 and DTIM1 Value, the Duty Cycle of PWM Signal is much more

accurate. Now, Just have to adjust PWM Signal frequency and check MOSFET Gate Driver Data Sheet to set the Dead Time.

Thanks

Jk