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TM4C1294NCPDT: What is the purpose of R50 in launchpad?

Robbie Valentine86
Expert 1550 points
Part Number: TM4C1294NCPDT

Hello,

I'm looking at the following schematics:

https://www.ti.com/lit/ug/spmu365c/spmu365c.pdf?ts=1595970961677&ref_url=https%253A%252F%252Fwww.ti.com%252Ftool%252FEK-TM4C1294XL

What is the purpose of R50 (2k resistor) in series with the oscillator path osc1?  Should this be a standard part of custom designs?

  • 0
    TI__Guru*** 135355 points

    Hello Robbie,

    I am going to use R49 as the example here since that is for the TM4C1294NCPDT that is at the core of the LaunchPad, whereas R50 is for the ICDI MCU.

    For R49, it is included based on our guidelines for using that specific 25 MHz crystal which can be found on Page 1841 of the device datasheet: https://www.ti.com/lit/ds/symlink/tm4c1294ncpdt.pdf 

    The crystal parameter table informs on both external capacitance and series resistance for each crystal we have validated for the device.

    You will need to check which crystal you are using to see if it needs the resistor and what value you need.