October 2003 P2811/12/14

rev


Alliance Semiconductor
2575, Augustine Drive • Santa Clara, CA • Tel: 408.855.4900 • Fax: 408.855.4999 • www.alsc.com
Notice: The information in this document is subject to change without notice.
Low-Power EMI Reduction IC

Features
ƒ FCC approved method of EMI attenuation
ƒ Provides up to 15 dB EMI reduction
ƒ Generates 1X, 2X, and 4X low EMI spread spectrum
clock of the input frequency
ƒ 1X: P2811, 2X: P2812, 4X: P2814
ƒ Optimized for input frequency range from 10 to 40
MHz P2811: 10 to 40 MHz P2812: 10 to 40 MHz
P2814: 10 to 40 MHz
ƒ Internal loop filter minimizes external components
and board space
ƒ Selectable spread options: Down Spread and Center
Spread
ƒ Low inherent cycle-to-cycle jitter
ƒ Eight spread % selections: ±0.625% to –3.5%
ƒ 3.3 V operating voltage
ƒ CMOS/TTL compatible inputs and outputs
ƒ Pinout compatible with Cypress CY25811,
CY25812, and CY25814
ƒ Products available for industrial temperature range
ƒ Available in 8-pin SOIC and TSSOP

Product Description
The P28xx is a versatile spread spectrum frequency
modulator designed specifically for input clock frequencies
from 10 to 40 MHz (see Input/Output Frequency Range
Selections). The P28xx can generate an EMI reduced clock
from crystal, ceramic resonator, or system clock. The
P28xx-A and P28xx-B offer various combinations of spread
options and percentage deviations (see Output Frequency
Deviation and Spread Option Selections section). These
combinations include Down Spread, Center Spread and
percentage deviation range from ±0.625% to -3.50%.
The P28xx reduces electromagnetic interference (EMI) at
the clock source, allowing a system wide EMI reduction for
all the down stream clocks and data dependent signals.
The P28xx allows significant system cost savings by
reducing the number of circuit board layers, ferrite beads,
shielding, and other passive components that are
traditionally required to pass EMI regulations.
The P28xx modulates the output of a single PLL in order to
“spread” the bandwidth of a synthesized clock, thereby
decreasing the peak amplitudes of its harmonics. This
results in significantly lower system EMI compared to the
typical narrow band signal produced by oscillators and
most clock generators. Lowering EMI by increasing a
signal’s bandwidth is called “spread spectrum clock
generation”.
The P28xx uses the most efficient and optimized
modulation profile approved by the FCC and is
implemented by using a proprietary all-digital method.

Applications
The P28xx is targeted towards EMI management for
memory interfaces in mobile graphic chipsets and high-
speed digital applications such as PC peripheral devices,
consumer electronics, and embedded controller systems.


Block Diagram