October 2003
rev
Low-Power EMI Reduction IC
Features
FCC approved method of EMI attenuation
Provides up to 15 dB EMI reduction
Generates 1X, 2X, and 4X low EMI spread spectrum
clock of the input frequency
1X: P2811, 2X: P2812, 4X: P2814
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
Internal loop filter minimizes external components
and board space
Selectable spread options: Down Spread and Center
Spread
Low inherent cycle-to-cycle jitter
Eight spread % selections: ±0.625% to –3.5%
3.3 V operating voltage
CMOS/TTL compatible inputs and outputs
Pinout
compatible
with
Cypress
CY25811,
CY25812, and CY25814
Products available for industrial temperature range
Available in 8-pin SOIC and TSSOP
P2811/12/14
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.
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.
Lowering EMI by increasing a
signal’s bandwidth is called “spread spectrum clock
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
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
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.
October 2003
rev
Pin Configuration
P2811/12/14
Pin Description
Pin#
1
2
3
SRS
4
5
6
7
8
VDD
XOUT
P
I
ModOut
FRS
O
I
I
Pin Name
XIN
VSS
D_C
Type
I
P
I
Description
Connect to externally generated clock signal or crystal.
Ground Connection. Connect to system ground.
Digital logic input used to select Down (LOW) or Center (HIGH) Spread
Options (see Output Frequency Deviation and Spread Option Selections).
This pin has an internal pull-up resistor.
Spread Range Selection. Digital logic input used to select frequency
deviation (see Output Frequency Deviation and Spread Option Selections).
This pin has an internal pull-up resistor.
Spread Spectrum clock output (see Input/Output Frequency Range
Selections and Output Frequency Deviation and Spread Option Selections).
Frequency Range Selection. Digital logic input used to select input fre-
quency range (see Input/Output Frequency Range Selections). This pin has
an internal pull-up resistor.
Connect to +3.3 V
Connect to crystal. No connect if externally generated clock signal is used.
Input/Output Frequency Range Selections
Pin 6
FRS
0
1
Part number
P2812 (2X)
Input
Output
(MHz)
(MHz)
10-20
20-40
20-40
40-80
Modulation
rate
Input frequency
/ 448
Input frequency
/ 896
P2811 (1X)
Input
Output
(MHz)
(MHz)
10-20
20-40
10-20
20-40
P2814 (4X)
Input
Output
(MHz)
(MHz)
10-20
20-40
40-80
80-160
Low Power EMI Reduction IC
Notice: The information in this document is subject to change without notice.
2 of 8
Microcontroller MCU
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