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TM4C1294KCPDT: What is Frequency Tolerance to Cause MOSCFAIL?

slugdoug
Prodigy 70 points
Part Number: TM4C1294KCPDT

What is the valid frequency range to cause a MOSCFAIL?  Is this the 5 to 25MHz listed in the spec?  If so, how far above 25MHz does the fault trip?  We are using a 25MHz crystal and want to verify we cannot cause this fault to occur with good parts.

  • 0
    TI__Guru**** 190806 points

    Hi,

      The datashseet only shows 25MHz as the maximum. It does not have a value beyond which a fault will trip. I think the internal PIOSC (with itself having some tolerance) is used to check if the MOSC is in the proper window and I don't think the window will be between 5 and 25MHz. There will be some tolerance built into it. Therefore, the window will be larger than 25MHz on the upper bound. The frequency beyond which the fault will really trip will depend on the operating condition (i.e. voltage, temperature). From the hardware point of view you should select the crystal with the recommended parameters listed in the datasheet. From the software point of view, you need to enable the CVAL bit in the MOSCCTL register and check if the MOSCFAIL bit in the RESC is set. 

  • 0
    Guru 117855 points

    Our small tech firm received a highly similar request from an active client.    In their case - they had a surplus of (both) crystals & crystal oscillators - and these 'exceeded their MCU spec by 10-15%!'    (Note: these were not this vendor's TM4C class devices - instead were ARM Cortex M4s from 2 different vendors.)

    In all cases - with 'fresh parts & at normal room temperature' - the MCUs operated w/in their basic specifications.    However - when we expanded our test to 'cold' (yet still w/in the MCU's operating spec) 80%+ of the oscillators at 15% above spec suffered 'failure' while that rate was 30% for the 10% above spec parts.    (fortunately - the MCUs were not operated for a prolonged period once the failure was noted - and 'few' (perhaps none) of the devices were permanently damaged...)

    As vendor's Charles noted: Temperature, Operating Voltage, Aging and Process Variation may influence device performance.    Device's (may) appear to work 'beyond spec' - yet as our example reveals - broad testing is required to 'properly inform & advise' such 'pushing of the device spec.'    (i.e. is 'best done' w/a known group of parts - all from a similar batch - and operated in a highly consistent manner...)     

    Down the road - such favorable performance cannot be guaranteed - and should only be attempted after a comprehensive testing program (operating the devices at their extremes - and in sufficient number & test duration) - before releasing the devices for a production build...