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TMS320F28034: Internal Pullup Resistor and Crystal Feedback Resistor

Genius 5300 points
Part Number: TMS320F28034

Hi experts,

My customer has created a board using the TMS320F28034. Let me check a few things about the device.

Can I assume that the value of the internal pullup resistor of the TMS320F28034 is as follows? (The value is calculated for GPIO from "7.6 Electrical Characteristics" in the datasheet.)

Max: 41.25kΩ
Typ: 23.57kΩ
Min: 16.09kΩ

They have attached a feedback resistor (Rf=1MΩ) to the circuit of the external crystal, but is the feedback resistor inside the microcontroller?
If they add an external feedback resistor, is there any possibility that something will go wrong?



Best regards,
O.H

  • Can I assume that the value of the internal pullup resistor of the TMS320F28034 is as follows? (The value is calculated for GPIO from "7.6 Electrical Characteristics" in the datasheet.)

    No, These are active circuits rather than resistors. 

    They have attached a feedback resistor (Rf=1MΩ) to the circuit of the external crystal, but is the feedback resistor inside the microcontroller?
    If they add an external feedback resistor, is there any possibility that something will go wrong?

    This resistor is not needed I would recommend removing. I am slightly unsure what effect it would have, if you would like me to inquire I can

    Regards,

    Cody 

  • Also to directly answer your feedback resistor question, Yes it is already inside the microcontroller. This external resistor will be in parallel with it. If the parallel resistor lowers the resistance too much the crystal's output will begin to clip, or stop oscillating altogether.

    Please remove this resistor.

    Regards,
    Cody 

  • Hi,

    Thanks for the reply.

    Of the multiple boards created by my customer, only one specific board is experiencing the following problem. WDCR is set to 0x68 to disable the WDT, but the WDT still resets the board. We checked the oscillation of the external crystal and found that the frequency is unintended.(The frequency has been changed from 10MHz to 100Hz).

    We will continue to make improvements based on the feedback we received, and will contact you if any problems or unclear points occur again.

    Best regards,
    O.H