MAX3622 Просмотр технического описания (PDF) - Maxim Integrated

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MAX3622

Low-Jitter, Precision Clock Generator with Two Outputs

Maxim Integrated 

Low-Jitter, Precision Clock Generator

with Two Outputs

+3.3V ±5%

VCC

10.5Ω

0.01μF

VCCA

0.01μF 10μF

Figure 2. Analog Supply Filtering

MAX3622

C9

C 10

Y1

25MHz

CRYSTAL

Applications Information

Power-Supply Filtering

The MAX3622 is a mixed analog/digital IC. The PLL

contains analog circuitry susceptible to random noise.

In addition to excellent on-chip power-supply noise

rejection, the MAX3622 provides a separate power-

supply pin, VCCA, for the VCO circuitry. Figure 2 illus-

trates the recommended power-supply filter network for

VCCA. The purpose of this design technique is to

ensure clean input power supply to the VCO circuitry

and to improve the overall immunity to power-supply

noise. This network requires that the power supply is

+3.3V ±5%. Decoupling capacitors should be used on

all other supply pins for best performance.

Crystal Selection

The crystal oscillator is designed to drive a fundamen-

tal mode, AT-cut crystal resonator. See Table 1 for rec-

ommended crystal specifications. See Figure 4 for

external capacitor connection.

Crystal Input Layout and Frequency

Stability

The crystal, trace, and two external capacitors should

be placed on the board as close as possible to the

MAX3622’s X_IN and X_OUT pins to reduce crosstalk

of active signals into the oscillator.

The layout shown in Figure 3 gives approximately 3pF

of trace plus footprint capacitance per side of the crys-

tal (Y1). The dielectric material is FR-4 and dielectric

thickness of the reference board is 15 mils. Using a

25MHz crystal and the capacitor values of C10 = 27pF

and C9 = 33pF, the measured output frequency accu-

racy is -10ppm at +25°C ambient temperature.

Figure 3. Crystal Layout

Table 1. Crystal Selection Parameters

PARAMETER

Crystal Oscillation Frequency

Shunt Capacitance

Load Capacitance

Equivalent Series Resistance

(ESR)

Maximum Crystal Drive Level

SYMBOL MIN

fOSC

CO

CL

RS

TYP

25

2.0

18

MAX

7.0

50

300

UNITS

MHz

pF

pF

μW

6 _______________________________________________________________________________________

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