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STM32L071CBT6 + LSE : ABS07-120-32.768kHz : Doesn't start

Question asked by Steph on May 31, 2017
Latest reply on Sep 27, 2017 by kermeci.levente

Hi, 

 

I've a design based on STM32L071CBT6, and I'm using an Abracon Crystal : ABS 07-120-32.768kHz as recommanded in AN2867.

Here's an overview on my PCB, two capacitor (C4 and C5) 2.2nF/COG/50V/5% with the oscillator X1 

 

From a SW point of view, I discover that troubles appear during execution of the function SystemClock_Config(void) :

TimeOut happen during execution of function HAL_RCC_OscConfig(&RCC_OscInitStruct), in LSE Configuration : 

 

/* Set the new LSE configuration -----------------------------------------*/
__HAL_RCC_LSE_CONFIG(RCC_OscInitStruct->LSEState);

/* Check the LSE State */
if((RCC_OscInitStruct->LSEState) != RCC_LSE_OFF)
   {
   /* Get timeout */
   tickstart = HAL_GetTick();

   /* Wait till LSE is ready */
   while(__HAL_RCC_GET_FLAG(RCC_FLAG_LSERDY) == RESET)
      {
        if((HAL_GetTick() - tickstart ) > RCC_LSE_TIMEOUT_VALUE)
            {
            return HAL_TIMEOUT;
            }      
      }
   }

 

I've tried to modify capacitors, 4.7pF, 10pF, or remove completly : no effet

 

I've add a line of code :

RCC_LSEDriveConfig(RCC_LSEDrive_LOW);  // Addes as mentionned in AN2867

HAL_RCC_OscConfig(&RCC_OscInitStruct); 

 

But it doesn't work, same problem

With these small capacitance, unable to measure with scope, ... do you have idea or feedback using this crytal, or regarding this configuration

 

Thanks for your help

 

Best regards

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