LPC5536 SCTIMER/PWM issues

CatFather — Mon, 18 Mar 2024 14:43:02 GMT

I am controlling a bldc motor with 3 sct ouptuts. This works fine until one of the thrree duty cycles reach 50-60%. After this point strange things happen and it might be that pulses get missing (see attached red curve) The SCTIMER_UpdatePwmDutycycle function is called every 50us. (PWM Frequency is 20kHz). If I increase the frequency to 50kHz it gets even worse. If I choose frequency 10kHz it gets better but this frequency is not suitable for my application.

This is how I initialize the SCTIMER:

sctimer_config_t sctimerInfo;

sctimer_pwm_signal_param_t pwmParam;

uint32_t sctimerClock;

s_PWMcallback = NoOp;

sctimerClock = CLOCK_GetFreq(kCLOCK_BusClk);

SCTIMER_GetDefaultConfig(&sctimerInfo);

sctimerInfo.enableBidirection_l = TRUE;

SCTIMER_Init(SCT0, &sctimerInfo);

// Configure PWM params with frequency 20kHZ from output

pwmParam.output = PWM_OUT_A;

pwmParam.level = kSCTIMER_HighTrue;

pwmParam.dutyCyclePercent = 0;

if (SCTIMER_SetupPwm(SCT0, &pwmParam, kSCTIMER_CenterAlignedPwm, PWM_FREQ_HZ, sctimerClock, &s_eventNumberOutputA) == kStatus_Fail)

{

SetDeviceStatusWithErrorNumber(ERR_BIT_INIZIALISATION, 2);

return ;

}

pwmParam.output = PWM_OUT_B;

pwmParam.level = kSCTIMER_HighTrue;

pwmParam.dutyCyclePercent = 0;

if (SCTIMER_SetupPwm(SCT0, &pwmParam, kSCTIMER_CenterAlignedPwm, PWM_FREQ_HZ, sctimerClock, &s_eventNumberOutputB) == kStatus_Fail)

{

SetDeviceStatusWithErrorNumber(ERR_BIT_INIZIALISATION, 3);

return ;

}

pwmParam.output = PWM_OUT_C;

pwmParam.level = kSCTIMER_HighTrue;

pwmParam.dutyCyclePercent = 0;

if (SCTIMER_SetupPwm(SCT0, &pwmParam, kSCTIMER_CenterAlignedPwm, PWM_FREQ_HZ, sctimerClock, &s_eventNumberOutputC) == kStatus_Fail)

{

SetDeviceStatusWithErrorNumber(ERR_BIT_INIZIALISATION, 4);

return ;

}

// Enable interrupt flag for event associated with out 4, we use the interrupt to update dutycycle

EnableInterruptPWM();

// Receive notification when event is triggered

SCTIMER_SetCallback(SCT0, SCTIMER_HANDLER, s_eventNumberOutputA);

NVIC_SetPriority(SCT0_IRQn, IRQPRIO_MOTOR_PWM); // prio[0..7] 0 is highest // Enable at the NVIC

EnableIRQ(SCT0_IRQn);

// Start the 32-bit unify timer

SCTIMER_StartTimer(SCT0, kSCTIMER_Counter_U);

And this is how I Update the pulse width(called from interrupt):

DisableInterruptPWM();

SCTIMER_UpdatePwmDutycycle(SCT0, PWM_OUT_A, (UInt8)(pwmA*100), s_eventNumberOutputA);

SCTIMER_UpdatePwmDutycycle(SCT0, PWM_OUT_B, (UInt8)(pwmB*100), s_eventNumberOutputB);

SCTIMER_UpdatePwmDutycycle(SCT0, PWM_OUT_C, (UInt8)(pwmC*100), s_eventNumberOutputC);

EnableInterruptPWM();

For any ideas I am very thankful.

Rico

Re: LPC5536 SCTIMER/PWM issues

CatFather — Tue, 19 Mar 2024 14:42:58 GMT

I managed to resolve this issue by commenting the update of MATCH register and just update the MATCHREL register

topic Re: LPC5536 SCTIMER/PWM issues in LPC Microcontrollers

LPC5536 SCTIMER/PWM issues

Re: LPC5536 SCTIMER/PWM issues