How to generate inteleave PWMs in MC56F82736

[Jim_Li]

Hi,

      I am working on a interleave totem-pole PFC circuit which needs two pairs of PWMs with 180 degree phase shift to each other.

     I have configure the PWM_SM0 to drive the phase 1 leg mosfets. How can I set the PWM_SM1 to have its counter a 180 degree from the first one's.  

[xiangjun_rong]

Hi,

Regarding the required PWM waveform of totem PFC, as the following figure I copied from AN12618.pdf.

You have to use the PWM_SM0_A and PWM_SM0_B signals to control the Q1 and Q2, the PWM_SM0_A and PWM_SM0_B signals are required to be complementary, this is so-called 180 phase-shift PWM signals. In other words, the Q1 and Q2 must be connected to the A and B of the same eFlexPWM sub-module PWM_SMx.

Regarding the SD1 and SD2 power device, you can connect them to another A and B of eFlexPWM sub-module, for example PWM_SM1_A and PWM_SM1_B signals, I think connecting GPIO pins to SD1 and SD2 is okay. As you know that eFlexPWM module supports software control mode, in other words, you can set/clear the PWM_SM1_A and PWM_SM1_B signals with software. In a main power half cycle, for example above a and b figures, you can clear the PWM_SMx_A signal to low to turn off SD1, but set the PWM_SMx_B signal to high to turn on SD2 in half main power cycle.

Hope it can help you

BR

XiangJun Rong

[Jim_Li]

Hi, Xiangjun,

Thank you for your reply.

The complementary PWM signal from one PWM SM is not what calls interleave. The two complemetary PWM signals have the duty of d and 1-d respectively.

The concept of interleave is that two PWM signal has the same duty but their phases have 180 degree shift. So it can extended the current of a AC/DC or DC/DC converter as well as reducing the total current ripple.

So in my implemented totem-pole topoloy,  there are two fast legs and one slow leg. And the two fast leg's PWM signal carry waves need 180 degree shift.

Actually I have realized the interleave function. I use the half cycle - VAL0 of SM0 to sync the SM1 initialization. So SM1 counter can be always half cycle delay from SM0, which achieves 180 degree shift.

 Still thanks a lot!

Best regards,

Jim.Li