ASM3P2811A/B and ASM3P2812A/B and ASM3P2814A/B
Low Power EMI Reduction IC
©2010 SCILLC. All rights reserved. Pu
blication Order Number:
OCTOBER 2010 – Rev. 2.1 ASM3P2811/D
Features
• FCC approved method of EMI attenuation
•
Provides up to 15dB EMI reduction
• Generates a 1x, 2x and 4x low EMI spread spectrum
clock of the input frequency
o 1x: ASM3P2811A/B
o 2x: ASM3P2812A/B
o 4x: ASM3P2814A/B
• Optimized for input frequency range from 10MHz to
40MHz
• Internal loop filter minimizes external components
and board space
• Selectable spread options:
o Down Spread and Center Spread
• 8 frequency deviation selections:
o ±0.625% to -3.5%
• Low inherent Cycle-to-Cycle Jitter
• 3.3V Operating Voltage
• CMOS/TTL compatible inputs and outputs.
• Pin-out compatible with Cypress CY25811, CY25812
and CY25814
• Available in 8-pin SOIC and TSSOP Packages
Pr
oduct Description
The ASM3P28XX devices are versatile spread spectrum
frequency modulators designed specifically for a wide
range of input clock frequencies from 10MHz to 40MHz.
Refer to Input/Output Frequency Range Selection Table.
The ASM3P28XX can generate an EMI reduced clock
from crystal, ceramic resonator, or system clock. The
ASM3P28XX-A and the ASM3P28XX-B offer various
combinations of spread options and percentage
deviations. Refer to Frequency Deviation and Spread
Selection Table. These combinations include Down and
Center Spread, and percentage deviation range from
±0.625% to -3.5%.
The ASM3P28XX reduces electromagnetic interference
(EMI) at the clock source, allowing system wide reduction
of EMI of downstream clock and data dependent signals.
The ASM3P28XX 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 ASM3P28XX modulates the output of a single PLL in
order to “spread” the bandwidth of a synthesized clock,
and more importantly, decreases 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 frequency generators. Lowering
EMI by increasing a signal’s bandwidth is called ‘spread
spectrum clock generation’.
The ASM3P28XX uses the most efficient and optimized
modulation profile approved by the FCC and is
implemented in a proprietary all-digital method.
Applications
The ASM3P28XX is targeted towards EMI management
for memory and LVDS interfaces in mobile graphic
chipsets and high-speed digital applications such as PC
peripheral devices, consumer electronics, and embedded
controller systems.
