HC705RC17GRSSLASHD datasheet(83/126 Pages) NXP

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MC68HC705RC17 — Rev. 2.0

General Release Specification

Phase-Locked Loop (PLL) Synthesizer

General Release Specification — MC68HC705RC17

Section 10. Phase-Locked Loop (PLL) Synthesizer

10.1 Contents

10.2

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83

10.3

Phase-Locked Loop Control Register. . . . . . . . . . . . . . . . . . . .85

10.4

Operation During Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . .87

10.5

Noise Immunity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87

10.2 Introduction

The phase-locked loop (PLL) consists of a variable bandwidth loop filter,

a voltage controlled oscillator (VCO), a feedback frequency divider, and

a digital phase detector. The PLL requires an external loop filter

capacitor (typically 0.1

µF) connected between XFC and V

DDSYN. This

capacitor should be located as close to the chip as possible to minimize

noise. VDDSYN is the supply source for the PLL and should be bypassed

to minimize noise. The VDDSYN bypass cap should be as close as

possible to the chip. VDDSYN should be at the same potential as VDD.

The phase detector compares the frequency and phase of the feedback

frequency (tFB) and the crystal oscillator reference frequency (tREF) and

generates the output, PCOMP, as shown in Figure 10-1. The output

waveform is then integrated and amplified. The resultant dc voltage is

applied to the voltage controlled oscillator. The output of the VCO is

divided by a variable frequency divider of 128, 64, 32, or 16 to provide

the feedback frequency for the phase detector.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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