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.
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
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