NB3N502

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4

APPLICATIONS INFORMATION

High Frequency CMOS/TTL Oscillators

The NB3N502, along with a low frequency fundamental

mode crystal, can build a high frequency CMOS/TTL output

oscillator. For example, a 20 MHz crystal connected to the

NB3N502 with the 5X output selected (S1 = L, S0 = H)

produces a 100 MHz CMOS/TTL output clock.

External Components

Decoupling Instructions

In order to isolate the NB3N502 from system power

supply, noise de−coupling is required. The 0.01

mF

GND on pins 2 and 3. It is recommended to place

de−coupling capacitors as close as possible to the NB3N502

device to minimize lead inductance. Control input pins can

GND planes on the board.

Series Termination Resistor Recommendation

A 33

W series terminating resistor can be used on the

CLKOUT pin.

Crystal Load Capacitors Selection Guide

The total on−chip capacitance is approximately 12 pF per

crystal should be used.

The device crystal connections should include pads for

small capacitors from X1/CLK to ground and from X2 to

stray capacitance of the board to match the nominally

Because load capacitance can only be increased in this

trimming process, it is important to keep stray capacitance

to a minimum by using very short PCB traces (and no vias)

between the crystal and device. Crystal load capacitors, if

needed, must be connected from each of the pins X1 and X2

(crystal)) must be matched by total load capacitance of the

the crystal (see Figure 3 and equations below).

R

12 pF

12 pF

G

Internal

to Device

X2

X1/CLK

Crystal

Example 1: Equal stray capacitance on PCB

Example 2: Different stray capacitance on PCB trace X1/CLK vs. X2

Figure 3. Using a Crystal as Reference Clock