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I have an existing design that uses a HC49U. What should I consider if I change to the smaller HC49S crystal, or an SMD crystal?

April 26, 2017crystal design existing hc49s hc49u smaller SMD uses

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I have an existing design that uses a HC49U. What should I consider if I change to the smaller HC49S crystal, or an SMD crystal?

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Drive Level – HC49U crystals are typically rated 1.0mW max, while the HC49S and most SMD crystals are rated at only 0.5mW or 0.1mW maximum. See question 11 for more information on exceeding the maximum drive level of a crystal. Pullability – some applications require tuning the frequency of the oscillator, either by mechanically or electrically changing the value of load capacitance. The HC49S and surface mount crystals have less pullability than the HC49U. It is important to verify whether the HC49S or the surface mount crystal will have sufficient pull range for the application. Generally, an HC49S has one-half the pullability as an HC49U. ESR – The Equivalent Series Resistance (ESR) is generally higher with the HC49S and surface mount crystals, and can cause a problem if the oscillator circuit does not have sufficient loop gain. 13.