This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TM4C1294KCPDT: About Main Oscillator Specifications

Genius 5300 points
Part Number: TM4C1294KCPDT

Hi,

My customer is considering replacing the crystal unit connected to the TTM4C1294KCPDTI3.
The specifications of C1 and C2 which are connected to OSC0 and OSC1 terminals are described in "Table 27 -23" in datasheet.
Table 27 -23 specifies Min 12pF to Max 24pF.
We understand that this value is defined by the load capacitance of the crystal unit connected to the OSC0 and OSC1 terminals.
Does it mean that the capacity within this specification (Min 12pF to Max 24pF) needs to be set as the TM4C1294KCPDT specifies this value?

In Table 27 -24, some model numbers (Example: NX5032 GA -16.000 MHZLN-CD -1) show values of 10pF for C1 and C2, which are out of specification(Min 12pF to Max 24pF) .
Could you tell me why the TM4C1294KCPDT specifies this value?

Currently, they are considering replacing it with a crystal oscillator with a load capacity of 6pF. In this case, the external capacitor capacitance of C1 and C2 is likely to be 8pF or 9pF, which deviates from the specifications of C1 and C2 in Table 27 -23.

Best Regards,
O.H

  • Hi,

    O.H said:
    In Table 27 -24, some model numbers (Example: NX5032 GA -16.000 MHZLN-CD -1) show values of 10pF for C1 and C2, which are out of specification(Min 12pF to Max 24pF) .
    Could you tell me why the TM4C1294KCPDT specifies this value?

      Although the 10pF is shown for the NX5032 cystal, this component was simulated and confirmed for operation. I agree with you that it is a bit out of the specified range in the table. 

    O.H said:

    In Table 27 -24, some model numbers (Example: NX5032 GA -16.000 MHZLN-CD -1) show values of 10pF for C1 and C2, which are out of specification(Min 12pF to Max 24pF) .
    Could you tell me why the TM4C1294KCPDT specifies this value?

    Currently, they are considering replacing it with a crystal oscillator with a load capacity of 6pF. In this case, the external capacitor capacitance of C1 and C2 is likely to be 8pF or 9pF, which deviates from the specifications of C1 and C2 in Table 27 -23.

    Is there any reason that your customer cannot choose a crystal with the bypass cap in the range listed in the table? The best way to confirm if the crystal is ok is for you or your customer to provide a sample of the product to the crystal manufacturer. They have the ability to measure and advise on bypass capacitors for their crystals. If the crystal manufacturer confirms bypass cap of 8-9pF is working then there is no issue with the MCU. 

  • Hi Charles,

    Thank you for your reply.

    >Does it mean that the capacity within this specification (Min 12pF to Max 24pF) needs to be set as the TM4C1294KCPDT specifies this value?
    Regarding the above question, from your answer:
    Is it correct to understand that "The capacitance values of C1 and C2 do not necessarily have to be within the specifications described in Table 27 -23(Min 12pF to Max 24pF)."?

    Charles Tsai said:
    Is there any reason that your customer cannot choose a crystal with the bypass cap in the range listed in the table? The best way to confirm if the crystal is ok is for you or your customer to provide a sample of the product to the crystal manufacturer. They have the ability to measure and advise on bypass capacitors for their crystals. If the crystal manufacturer confirms bypass cap of 8-9pF is working then there is no issue with the MCU. 

    They are studying the specification of a crystal oscillator with a load capacity of 6pF for other substrates, and they are thinking about using it for this substrate as well.
    I understood that "If the crystal manufacturer confirms bypass cap of 8-9pF is working then there is no issue with the MCU."

    Best Regards,
    O.H

  • Hi,

    O.H said:
    Is it correct to understand that "The capacitance values of C1 and C2 do not necessarily have to be within the specifications described in Table 27 -23(Min 12pF to Max 24pF)."?

      I tend to think that the table is giving a range (12-24pF) for majority of components that have been simulated and confirmed to work with the MCU. If the crystal manufacturer confirms the bypass cap to be working which happens to be a bit outside the range, then I think it should be no problem. 

      When I look at the TM4C123 LaunchPad, it is actually using a 10pF bypass cap.

  • Hi

    I missed the LaunchPad schematic.
    Thanks to your support, I understood!

    Best Regards,
    O.H