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TMS320F280049: The influence of X2/GPIO18 Pin Pullup Current during power up on the external crystal or resonator.

Will Gao
Intellectual 2335 points

Part Number: TMS320F280049

Hi experts, 

In the errata note of F28004x, it said "During power up, a pullup current of approximately 1.8 mA will be seen on X2/GPIO18.". And since there is no workaround for this problem, the customer wants to know what influence will be on the external crystal circuit or resonator with this pullup current? And the time duration of this pullup current 1.8 mA. Thanks. 

Best Regards, 

Will 

  • 0
    TI__Intellectual 2335 points

    On the other hand, I am also curious about the measurement method or condition of this 1.8 mA pullup current, i.e. the external impedance of the pin for this 1.8 mA, if the external condition changed, the pullup current will also be 1.8 mA?

    Best Regards, 

    Will  

  • 0 in reply to Will Gao
    TI__Guru* 95315 points

    Will,

        I need to reach out to the Design team for an answer on this. Will try to get an answer by next week.

  • 0 in reply to Will Gao
    TI__Expert 5900 points

    Will,

    There will be no problem with the customer using an external crystal or resonator on this pin, that is the intended use.  The Errata is noting that the X2 XTAL output will be active during the reset phase of the device (until XRSn is released by the POR circuit or any external circuit).  This would only be problematic for PCB designs which use X2/GPIO18 as a GPIO18 which could have contention with any external digital logic.  Since this application is using X2 as a XTAL, everything will be fine and the crystal will begin oscillation when it is enabled in software.  No crystal damage or other ill effects are possible.

    Also, the 1.8mA is a typical value and will drop to 0A when the pin voltage raises to VDDIO (consider it a pullup resistor).

    Best regards,

    Jason