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TMS320F28235: External 20MHz crystal doubt

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Replies: 2

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Part Number: TMS320F28235


Customer is using F28235 Q100 for their application. 20MHz external crystal is used.

Here are some doubts:

1) Can 20MHz be used? It should be OK.

2) What's the recommendation for CL and other specifications?

Thanks a lot.

Br, Jordan

  • Jordan,

    The max PLL multipler is 10/2.  You will only be able to achieve 100 MHz operation with a 20 MHz crystal.  You can use 20 MHz with that restriction.

    Normally, people use 30 MHz crystal with F28235 to achieve 150 MHz operation.



    David M. Alter
    Senior Member Technical Staff
    Texas Instruments Inc.

  • In reply to David M. Alter:

    The parameters for the passive components vary based on the crystal chosen. Hence we do not recommend any values. Our datasheet has the following note:

    TI recommends that customers have the resonator/crystal vendor characterize the operation of their device with the DSC chip. The resonator/crystal vendor has the equipment and expertise to tune the tank circuit. The vendor can also advise the customer regarding the proper tank component values that will produce proper start-up and stability over the entire operating range.


    Hareesh J, C2000 Microcontroller Applications, Texas Instruments.

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