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TM4C1290NCPDT: Crystal start-up time

Shaofeng Luo
Intellectual 1630 points
Part Number: TM4C1290NCPDT

Hi expert

Our customers are using TM4C1290, and they want to use crystal for low cost design. However, they found that sometimes the MCU will be stuck and debugger can't link it. And at last we found the start-up time of crystal is about 30ms. Is it the root cause? And what's your suggestion to minimize the start-up time?

  • 0
    TI__Guru**** 184446 points

    Hi Shaofeng,

    Shaofeng Luo said:
    And at last we found the start-up time of crystal is about 30ms. Is it the root cause? And what's your suggestion to minimize the start-up time?

      Can you provide more information?

    - Datasheet shows the startup time to be 18ms max. If you measure 30ms then it is exceeding the spec. 

    - How many boards do you see the problem?

    - Do you have any boards that don't have the problem? Or all boards have the problem?

    - If there are any boards that do NOT have the problem then what startup time do you measure on them?

    - What are the load capacitors on the board? See below details. 

    - Has the customer used one of crystals or at least one that is very close for the mentioned crystal parameters that is listed on the datasheet electrical specs? See below.  

    - Can you show how the clock is initialized on their code?

  • 0 in reply to Charles Tsai
    TI__Intellectual 1630 points

    Hi Charles

    Got it, the crystal specs are as below, please help to check it. We tried a series Cload, 10pF~20pF, but it doesn't work.

    We grabbed some waveforms as below: 

    You can see the X1 is low, lasting for several ms. What's the standard power-up waveform for TM4C1290?

  • 0 in reply to Shaofeng Luo
    TI__Guru**** 184446 points

    Hi Shaofeng,

      I have no expertise with crystals to know what is wrong with your particular crystal. All I can say is that in the datasheet there are various crystals that have been simulated and confirmed to operate within the specifications of Main Oscillator Input Characteristics. The one you have chosen is a 20Mhz crystal and it is not listed in the table. You will need to consult with the crystal vendor on what C1 and C2 are the values of the load capacitors that should be put on each leg of the crystal pins to ensure oscillation at the correct frequency given the MOSC input characteristics. They will have the best knowledge. 

    Table 26-24 on page 1583 lists part numbers of crystals that have been simulated and confirmed to
    operate within the specifications in Table 26-23 on page 1581. Other crystals that have nearly identical
    crystal parameters can be expected to work as well.