deadtime on 100%duty of flexPWM in MPC5744P

[liujinhang]

hi everyone,

i found a problem about 100% duty of flexPWM in MPC5744P.

when initial the flexPWM, i set below:

#define FlexPWM0_DTSRCSEL          0x0000u    

#define FlexPWM0_MCTRL                 0xff00u //PWM45 ( PWM submodule ) is used to generate complementary PWM pair. 

#define FlexPWM0_CTRL2_sub0         0xc2A0u  //PWMA and PWMB form a complementary PWM pair.
#define FlexPWM0_INIT_sub0             0xF060u

#define FlexPWM0_VAL1_sub0           0x0FA0u    //period is 8000

#define FlexPWM0_OCTRL_sub0       0x0610u    //invert PWMA, invert PWMB

#define FlexPWM0_DTCNT0_sub0     112u          //PWM A dead time
#define FlexPWM0_DTCNT1_sub0     112u          //PWM B dead time

then i set the "FlexPWM0_VAL4_sub0   = 0xF060u;" and  "FlexPWM0_VAL5_sub0   = 0x0FA0u    ;"  

in my opinion, i think the PWMB will output 100% duty and PWMA will output 0% duty, but i strangely found that PWMB output 100% duty but PWMA output not 0% duty. the PWMA scope like below:

i measured the high level time pluse is equal to the deadtime set in FlexPWM0_DTCNT0_sub0. to verify the relationship between FlexPWM0_DTCNT0_sub0 and PWMA, i set "FlexPWM0_DTCNT0_sub0 = 0" and then the PWMA can output 0% duty successfully.

in this case, my problem is three:

1. why PWMA cannot complementary from PWMB all the time?

2. when i set PWMB 100% duty, how the relationship between FlexPWM0_DTCNT0_sub0 and PWMA appeared? 

3. if the "FlexPWM0_DTCNT0_sub0 = 0", is there any risk exists in my high bridge and low bridge motor control circle application?

please help me , thank you very much.

[PetrS]

Hi,

With your setting

#define FlexPWM0_INIT_sub0             0xF060u

#define FlexPWM0_VAL1_sub0           0x0FA0u   

the period is 8000+1.

Using the FlexPWM0_VAL4_sub0   = 0xF060u;" and  "FlexPWM0_VAL5_sub0   = 0x0FA0u you do not have 100% duty cycle on PWM45, but there is low pulse with length of single PWM clock. That’s why you see such pulse on PWMA after deadtime insertion logic. Look at Figure 40-148. "Deadtime Insertion and Fine Control Logic" of the device RM to know how deadtime is inserted.

Set FlexPWM0_VAL5_sub0   = 0x0FA1u to get 100% duty.

BR, Petr

[liujinhang]

hi petr,

thanks for your response.

but i have tested my project follow your idea, the problem still exists.

can you give me a demo project, that really realize the 100% duty in flexPWM0_sub0/2/3 with a complementary PWM pair of PWMA and PWMB?  and the demo project is better to use VAL45 to make complementary.

may be there are some other reason coursing my problem. i can compare your demo project with mine to find out it.

[PetrS]

try this...

static void FlexPWM_Init(void)
{
    /* Submodule 0 Initialisation */
    FlexPWM_0.OUTEN.R           = 0x110;    // enable A and B outputs on submodule 0

    FlexPWM_0.SUB[0].CTRL1.R     = 0x0400;    // full cycle reload, every opportunity,IPBus/1
    FlexPWM_0.SUB[0].CTRL2.R    = 0x8080;    // debug and force enable
    
    FlexPWM_0.SUB[0].INIT.R   = 0xF060;        // PWM modulo
    FlexPWM_0.SUB[0].VAL1.R   = 0x0FA0;        // PWM modulo
    FlexPWM_0.SUB[0].VAL2.R   = -200;       // PWM A0 rising edge
    FlexPWM_0.SUB[0].VAL3.R   = 200;        // PWM A0 falling edge
    FlexPWM_0.SUB[0].VAL4.R   = 0xF060;        // PWM B0 rising edge
    FlexPWM_0.SUB[0].VAL5.R   = 0x0FA0+1;    // PWM B0 falling edge

    FlexPWM_0.SUB[0].DTCNT0.R   = 112;        // deadtime values
    FlexPWM_0.SUB[0].DTCNT1.R   = 112;

    FlexPWM_0.SUB[0].OCTRL.R = 0x0610;         //invert PWMA, invert PWMB
    
    FlexPWM_0.SUB[0].DISMAP.R   = 0x0000;    // disable fault pin condition

    FlexPWM_0.MCTRL.R = 0x1100;        // PWM45 is used to generate complementary PWM pair.
                                        // Submodule 0 PWM generator enabled

    FlexPWM_0.SUB[0].CTRL2.B.FORCE = 1; // generate FORCE to take MCTRL[IPOL] effect

    FlexPWM_0.MCTRL.B.LDOK = 0x1;    // Load the PRSC bits of CTRL1 and the INIT, and VALx registers
                        // into a set of buffers
    
}