A2181A-08TT Alliance Semiconductor, A2181A-08TT Datasheet - Page 4

• Manufacturer Part Number: A2181A-08TT
• Description: 3.3 V, 3 MHz to 78 MHz, general purpose EMI reduction IC
• Manufacturer: Alliance Semiconductor

October 2003
rev 1.0
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 78 MHz 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.
Note: Both logic input pins FS1 and FS0 have to be connected to either VDD or VSS. Do not leave
them floating.
Notice: The information in this document is subject to change without notice.
General Purpose EMI Reduction IC
P2781/82/84
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