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Question: Can the XIN input be driven from a 3.3V CMOS input signal?
Answer: Generally, the XIN input can be driven with a single-ended input signal, but it needs to be AC coupled. This is because the input stage is self-biased and also does some oscillator related calibration that would not tolerate a DC coupled signal. The self-biasing voltage (after the AC cap) is ~2V. The device power supply is 3.3V Therefore, the actual input signal swing after the AC coupling cap needs to be limited to roughly the supply rails. With an input signal swing of ~2.5V this requirement is satisfied. The tolerance of this 2.5V signal may be as large as +10% and as low as -30%.
One can not use a 3.3V CMOS signal directly to drive the CDCM61004 input, as the input signal would violate the absolute max rating. Calculation example:
Assume a supply case of VCC_IN=3.0V. Further assume 2.0V internal self-biasing. The input signal could be as high as 3.6V CMOS, causing a total input terminal voltage after the AC coupling cap of 2.0V+3.3V/2=3.8V. This would exceed the absolute max rating of the device of VCC_IN+0.5V.
Instead one should use a resistor divider to reduce the 3.3V output swing to 2.5V.
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