GPIO_InitTypeDef  GPIO_InitStructure;
   TIM_TimeBaseInitTypeDef TIM_TimeBase_InitStructure;
   TIM_OCInitTypeDef TIM_OC_InitStructure;

     //Initialize clocks for TIM2
     RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);

     //Initialize clocks for GPIOA, AFIO
     RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);

     //Configure pin TIM2 CH4 = PA3 as alternative function push-pull
     GPIO_InitStructure.GPIO_Pin = GPIO_Pin_3;
     GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
     GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
     GPIO_Init(GPIOA, &GPIO_InitStructure);

     //Configure TIM2 time base
     TIM_TimeBase_InitStructure.TIM_ClockDivision = TIM_CKD_DIV1;
     TIM_TimeBase_InitStructure.TIM_CounterMode = TIM_CounterMode_CenterAligned1;
     TIM_TimeBase_InitStructure.TIM_Period = 1024-1;  //11kHz with F100RB, 35kHz with F103RB
     TIM_TimeBase_InitStructure.TIM_Prescaler = 0;

     TIM_TimeBaseInit(TIM2, &TIM_TimeBase_InitStructure);

     //Configure TIM2 waveform
     TIM_OC_InitStructure.TIM_OCMode = TIM_OCMode_PWM1;
     TIM_OC_InitStructure.TIM_OCIdleState = TIM_OCIdleState_Reset;
     TIM_OC_InitStructure.TIM_OCNIdleState = TIM_OCNIdleState_Reset;
     TIM_OC_InitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
     TIM_OC_InitStructure.TIM_OCNPolarity = TIM_OCNPolarity_High;
     TIM_OC_InitStructure.TIM_OutputState = TIM_OutputState_Disable;
     TIM_OC_InitStructure.TIM_OutputNState = TIM_OutputNState_Disable;

     TIM_OC_InitStructure.TIM_Pulse = 512;

     TIM_OC4Init(TIM2, &TIM_OC_InitStructure);


     TIM_Cmd(TIM2, ENABLE);