stm32 pwm经过八个周期后失灵

IdelMan

今天碰到一个很奇怪的问题，希望大佬们帮助问题如下：
使用stm32的TIM3_CH2通道输出pwm控制电机，驱动板是tb6621fng，发现前八个周期都会按照程序正常输出，但是8个周期后，就一直输出高电平。
程序如下：
void TIM3_PWM_Init(u16 arr,u16 psc, u16 pulse){
    GPIO_InitTypeDef GPIOA_InitStruct;
    TIM_TimeBaseInitTypeDef TIM3_TimeBaseInitStruct;
    TIM_OCInitTypeDef TIM3_OCInitStruct;
   
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);
   
   
    GPIOA_InitStruct.GPIO_Mode = GPIO_Mode_AF_PP;
    GPIOA_InitStruct.GPIO_Pin = GPIO_Pin_7;
    GPIOA_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(GPIOA, &GPIOA_InitStruct);
   
   
    TIM3_TimeBaseInitStruct.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM3_TimeBaseInitStruct.TIM_CounterMode = TIM_CounterMode_Up;
    TIM3_TimeBaseInitStruct.TIM_Period = arr - 1;
    TIM3_TimeBaseInitStruct.TIM_Prescaler = psc - 1;
    TIM3_TimeBaseInitStruct.TIM_RepetitionCounter = 0;
    TIM_TimeBaseInit(TIM3, &TIM3_TimeBaseInitStruct);
   
   
    TIM3_OCInitStruct.TIM_OCMode = TIM_OCMode_PWM1;
    TIM3_OCInitStruct.TIM_OutputState = TIM_OutputState_Enable;
    TIM3_OCInitStruct.TIM_Pulse = pulse;
    TIM3_OCInitStruct.TIM_OCNPolarity = TIM_OCPolarity_High;
    TIM_OC2Init(TIM3, &TIM3_OCInitStruct);
    TIM_OC2PreloadConfig(TIM3, TIM_OCPreload_Enable);
    TIM_Cmd(TIM3, ENABLE);
    TIM_ARRPreloadConfig(TIM3, ENABLE);
}

int main()
{
    TIM3_PWM_Init(4000,72, 2000);
    while(1)
    {        
        
    }
}