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Zakładka z wyszukiwarką danych komponentów |
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Zakładka z wyszukiwarką danych komponentów |
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HA7210IP Arkusz danych(PDF) 6 Page - Intersil Corporation |
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HA7210IP Arkusz danych(HTML) 6 Page - Intersil Corporation |
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6 / 15 page  6 Crystal Pullability Figure 4 shows the basic equivalent circuit for a crystal and its loading circuit. Where: CM = Motional Capacitance LM = Motional Inductance RM = Motional Resistance C0 = Shunt Capacitance If loading capacitance is connected to a Series Mode Crystal, the new Parallel Mode frequency of resonance may be calculated with the following equation: Where: fP = Parallel Mode Resonant Frequency fS = Series Mode Resonant Frequency In a similar way, the Series Mode resonant frequency may be calculated from a Parallel Mode crystal and then you may calculate how much the frequency will “pull” with a new load. Layout Considerations Due to the extremely low current (and therefore high impedance) the circuit board layout of the HA7210 must be given special attention. Stray capacitance should be minimized. Keep the oscillator traces on a single layer of the PCB. Avoid putting a ground plane above or below this layer. The traces between the crystal, the capacitors, and the OSC pins should be as short as possible. Completely surround the oscillator components with a thick trace of VDD to minimize coupling with any digital signals. The final assembly must be free from contaminants such as solder flux, moisture, or any other potential source of leakage. A good solder mask will help keep the traces free of moisture and contamination over time. Further Reading Al Little “HA7210 Low Power Oscillator: Micropower Clock Oscillator and Op Amps Provide System Shutdown for Battery Circuits”. Intersil Corporation Application Note AN9317. Robert Rood “Improving Start-Up Time at 32kHz for the HA7210 Low Power Crystal Oscillator”. Intersil Corporation Application Note AN9334. S. S. Eaton “Timekeeping Advances Through COS/MOS Technology”. Intersil Corporation Application Note ICAN-6086. E. A. Vittoz, et. al. “High-Performance Crystal Oscillator Circuits: Theory and Application”. IEEE Journal of Solid- State Circuits, Vol. 23, No. 3, June 1988, pp774-783. M. A. Unkrich, et. al. “Conditions for Start-Up in Crystal Oscillators”. IEEE Journal of Solid-State Circuits, Vol. 17, No. 1, Feb. 1982, pp87-90. Marvin E. Frerking “Crystal Oscillator Design and Temperature Compensation”. New York: Van Nostrand- Reinhold, 1978. Pierce Oscillators Discussed pp56-75. C1 C2 2 OSC IN 3 OSC OUT VDD C0 CM LM RM FIGURE 4. C CL 1 1 C 1 ------- 1 C 2 ------- + --------------------------- Equivalent Crystal Load == f P f S 1 C M 2C 0 C CL + () ---------------------------------- + = HA7210 |
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