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CC1200EMK-868-930: Capacitance value for pin#32 EXT_XOSC

Koichiro Tashiro
Mastermind 21140 points
Part Number: CC1200EMK-868-930
Other Parts Discussed in Thread: CC1200

Hi,

My customer uses CC1200 in production.
The RF clock is supplied from pin#32 EXT_XOSC.
Clipped sine output TCXO is connected to this pin through the capacitor.

In TI reference design, 22pF is used as recommended capacitance value.
If 150pF capacitor is used mistakenly, what device parameters/features are impacted and how?

Thanks and regards,
Koichiro Tashiro

  • 0
    TI__Guru**** 317180 points

    When a TCXO starts up, the output will not be a perfect clipped sine from first clock cycle, it needs some time to stabilize. To avoid that a clock signal is not 50 % starts clocking the internal module the clock signal goes first through a ripple counter. The designer of the oscillator module was worried about the ripple counter being to short if a larger cap than 22 pF was selected. A 150 pF will most likely work in most cases but with a TCXO will slow start-up (low temp etc) it is a small risk that the chip will not start up as wanted.  

  • 0 in reply to TER
    TI__Mastermind 21140 points

    Hi TER,

    Thanks for your quick reply.
    Customer understood there is a small risk CC1200 cannot start up due to slow TCXO start-up.
    This risk can be avoided if CC1200 reset is applied after the elapse of enough stabilization time at each power-up?

    Thanks and regards,
    Koichiro Tashiro

  • 0 in reply to Koichiro Tashiro
    TI__Guru**** 317180 points

    The reset is async so from my understanding a reset should be enough to get the chip out of any unwanted states.