## Overview of PLL500-47SC-R The **PLL500-47SC-R** is a high-performance, low-phase noise VCXO (Voltage Controlled Crystal Oscillator) IC designed by Microchip Technology (formerly PhaseLink). It is specifically engineered to pull a high-frequency fundamental crystal to generate a low-jitter output clock. --- ### 1. Key Technical Specifications | Parameter | Specification | | :--- | :--- | | **Function** | Low Phase Noise VCXO | | **Input Frequency** | 17MHz to 36MHz (Fundamental Crystal) | | **Output Frequency** | Same as Crystal Frequency | | **Operating Voltage** | 3.3V (± 10%) | | **Output Type** | CMOS | | **Package** | SOP-8 (Standard 8-pin Small Outline) | | **Pulling Range** | Up to ± 200 ppm (typical) | | **Operating Temp** | 0°C to +70°C (Commercial) | --- ### 2. Internal Components & Pinout The device integrates several critical electronic sections into a single 8-pin package to minimize external component count. #### Pin Configuration Table | Pin # | Symbol | Description | | :--- | :--- | :--- | | 1 | V_IN | Voltage Control Input for frequency pulling. | | 2 | NC/SEL | No Connect or Select (depending on sub-variant). | | 3 | GND | Ground connection. | | 4 | XIN | Crystal Input connection. | | 5 | XOUT | Crystal Output connection. | | 6 | VDD | Positive Power Supply (3.3V). | | 7 | CLKOUT | CMOS Clock Output. | | 8 | OE | Output Enable (High = Enable, Low = High Impedance). | --- ### 3. Functional Blocks 1. **VCXO Varactor:** An internal variable capacitance (varactor) diode that changes its capacitance based on the voltage at the $V_{IN}$ pin. This shifts the crystal's resonant frequency. 2. **Crystal Oscillator Circuit:** A high-gain Pierce oscillator design optimized for High-Frequency Fundamental (HFF) crystals. 3. **Output Buffer:** A CMOS driver capable of driving 15pF loads with fast rise and fall times, ensuring signal integrity for digital circuits. 4. **Control Logic:** Includes the Output Enable (OE) function to put the chip into a low-power state or disconnect the clock from the bus. --- ### 4. Common Applications * **Set-Top Boxes:** Frequency synchronization for video processing. * **xDSL / Cable Modems:** Maintaining timing for high-speed data transmission. * **Audio/Video Equipment:** Reducing "jitter" in digital-to-analog conversions. * **Instrument Reference:** High-stability reference clocks for measurement tools. --- ### 5. Design Considerations * **Decoupling:** A 0.1µF ceramic capacitor should be placed as close as possible to the $V_{DD}$ and $GND$ pins to filter power supply noise. * **Crystal Selection:** To achieve the rated pulling range, the crystal should have a low $C_0/C_1$ ratio. * **PCB Layout:** Keep the traces between the crystal and the XIN/XOUT pins as short as possible to prevent parasitic capacitance from affecting the pulling range.