I2781AF-08ST 查看數據表（PDF） - ON Semiconductor

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I2781AF-08ST

General Purpose EMI Reduction IC

ON Semiconductor 

P2781/82/84

Spread Spectrum Selection

The P278xA performs Zero Cycle Slip when set at low percentage spreading. This allows no 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: the center frequency is the frequency of the external reference input on CLKIN, Pin 1.)

The P2781A is designed for PC peripheral, networking, notebook PC, and LCD monitor applications. It is optimized for

operation between 3 to 78MHz range. In the following application schematic example, the P2781A spread percentage

selection is determined by the external LF value specified in the Loop Filter Selection Table. The Input Frequency Selection

Table specifies the input frequency range. The external LF allows the user to fine tune the spread percentage to optimize the

EMI reduction benefits of the spread spectrum.

+3.3V

16 MHz

1 XIN/CLKIN VDD 8

2 XOUT

FS0 7

2.2 K

0.1µF

3 FS1 ModOUT 6

4 LF

VSS 5

R1

P278xA

C2

C1

0 Ohm

Modulated 16MHz Clock

To target Chip

Note: Both logic input pins FS1 and FS0 have to be connected to either VDD or VSS. Do not leave them floating.

Rev. 2 | Page 4 of 8 | www.onsemi.com

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