June 2005

P2779A

rev 0.1

Low-Cost Notebook EMI Reduction IC

3 of 8

Notice: The information in this document is subject to change without notice.

Spread Spectrum Selection

The P2779A performs zero cycle slip when set at low percentage spreading. This prevents any occurrence of system timing

error. The optimal setting should minimize system EMI to the fullest without affecting system performance. The spreading is

described as a percentage deviation of the center frequency. (Note that the center frequency is the frequency of the external

reference input on XIN/CLKIN, pin 1.)

The P2779A is designed for PC peripheral, networking, notebook PC, and LCD monitor applications. It is optimized for

operation from 20MHz to 38MHz. The P2779A’s spread percentage selection is determined by the external LF value

specified in the Loop Filter Selection Table. The external LF allows the user to fine tune the spread percentage to optimize

the EMI reduction benefits of the spread spectrum.

Application Schematic

PD selection: Power dissipation can be reduced by completely turning off the IC.

1

2

3

4

8

7

6

5

VDD

REF

ModOUT

VSS

LF

PD

XOUT

XIN/CLKIN

P2779A

+3.3V

Modulated 27MHz

27 MHz

C2

C1

R1

0.1µF

VDD