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SY89531LHZ Datasheet(PDF) 10 Page - Micrel Semiconductor |
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SY89531LHZ Datasheet(HTML) 10 Page - Micrel Semiconductor |
10 / 16 page 10 Precision Edge® SY89531L Micrel, Inc. M9999-010808 hbwhelp@micrel.com or (408) 955-1690 Crystal Input and Oscillator Interface The SY89531L features a fully integrated on-board oscillator to minimize system implementation costs. The oscillator is a series resonant, multivibrator type design, and thus, a series-resonant crystal is preferred, but not required. A parallel-resonant crystal can be used with the SY89531L with only a minor error in the desired frequency. A parallel- resonant mode crystal used in a series resonant circuit will exhibit a frequency of oscillation a few hundred ppm lower than specified; a few hundred ppm translates to kHz inaccuracies. In a general computer application this level of inaccuracy is immaterial. As the oscillator is somewhat sensitive to loading on its inputs, the user is advised to mount the crystal as close to the SY89531L as possible to avoid any board level parasitics. In addition, trace lengths should be matched. Figure 2 shows how to interface with a crystal. Table 1 illustrates the crystal specifications. Certain crystals may require a 10pF capacitor across XTAL1 and XTAL2 for proper operation. This is normally not required, but it is recommended that provisions be made for it. SY89531L XTAL2 (Pin 26, SOIC) XTAL1 (Pin 25, SOIC) XTAL 16.666MHz Quartz Crystal Selection: (1) Raltron Series Resonant: AS-16.666-S-SMD-T-MI (2) Raltron Parallel Resonant: AS-16.666-18-SMD-T-MI Optional Figure 2. Crystal Interface External Loop Filter Considerations The SY89531L features an external PLL loop filter that allows the user to tailor the PLL’s behavior to their application and operating environment. We recommend using ceramic capacitors with NPO or X7R dielectric, as they have very- low effective series resistance. For applications that require ultra-low cycle-to-cycle jitter, use the components shown in Figure 3. The PLL loop bandwidth is a function of feedback divider ratio, and the external loop filter allows the user to compensate. For instance, the PLL’s loop bandwidth can be decreased by using a smaller resistor in the loop filter. This results in less noise from the PLL input, but potentially more noise from the VCO. Refer to “AC Electrical Characteristics” for target PLL loop bandwidth. The designer should take care to keep the loop filter components on the same side of the board and as close as possible to the SY89531L’s LOOP_REF and LOOP_FILTER pins. To insure minimal noise pick up on the loop filter, it is desirable to cut away the ground plane directly underneath the loop filter component pads and traces. However, the benefit may not be significant in all applications and one must be careful to not alter the characteristic impedance of nearby traces. 470pF Loop Filter Loop Reference 330 Ω 0.2 µF Figure 3. External Loop Filter Connection Table 1. Quartz Crystal Oscillator Specifications Output Frequency: 14MHz-18MHz Mode of Oscillation: Fundamental Min Typ Max Unit Frequency Tolerance @25 °C — ±30 ±50 ppm Frequency Stability over 0 °C to 70°C — ±50 ±100 ppm Operating Temperature Range –20 — +70 °C Storage Temperature Range –55 — +125 °C Aging (per yr/first 3 yrs) —— ±5 ppm Load Capacitance — 18 (or series) — pF Equivalent Series Resistance (ESR) —— 50 Ω Drive Level — 100 — µW |
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