October 2003
rev 1.0
ASM3P2821B
Features
FCC approved method of EMI attenuation.
Generates a 1X low EMI spread spectrum clock of
the input frequency.
Input frequency range: 15MHz 鈥?27MHz.
Internal loop filter minimizes external components
and board space.
Frequency deviation: -2.5%
Low inherent cycle-to-cycle jitter.
3.3V operating voltage.
TTL or CMOS compatible inputs and outputs.
Ultra-low power CMOS design.
o
Pinout
range.
Available in 8-pin SOIC and TSSOP.
TBD mA @ 3.3V, 24MHz
compatible
with
Cypress
CY25811.
The ASM3P2821B reduces electromagnetic interference
(EMI) at the clock source, allowing system wide reduction
of EMI of
down stream clock and data dependent
signals. The ASM3P2821B 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 ASM3P2821B uses the most efficient and optimized
modulation profile approved by the FCC and is
implemented in a proprietary all digital method.
The ASM3P2821B modulates the output of a single PLL
in order to 鈥渟pread鈥?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鈥檚 bandwidth is called 鈥榮pread
spectrum clock generation鈥?
Products are available for industrial temperature
Product Description
The ASM3P2821B is a versatile spread spectrum
frequency modulator designed specifically for input clock
frequencies in the range of 15MHz - 27MHz. The
ASM3P2821B can generate an EMI reduced clock from a
ceramic resonator or system clock. The ASM3P2821B
offers a percentage deviation of 鈥?.5%.
Applications
The ASM3P2821B is targeted towards EMI management
for high speed digital applications such as PC peripheral
devices, consumer electronics and embedded controller
systems.
Block Diagram
VDD
Modulation
XIN
Crystal
Oscillator
PLL
Frequency
Divider
Feedback
Divider
Phase
Detector
Loop
Filter
VCO
Output
Divider
MODOUT
VSS
Alliance Semiconductor
2575, Augustine Drive
鈥?/div>
Santa Clara, CA
鈥?/div>
Tel: 408.855.4900
鈥?/div>
Fax: 408.855.4999
鈥?/div>
www.alsc.com
Notice: The information in this document is subject to change without notice.
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