ASM3P2872A
Peak EMI
Reducing Solution
©2010 SCILLC. All rights reserved. Pu
blication Order Number:
OCTOBER 2010 – Rev. 2.1 ASM3P2872/D
Features
• Generates an EMI optimized clock signal at the
o
utput.
• Integrated loop filter components.
• Operates with a 3.3V / 2.5V supply.
• Operating current less than 6mA.
• CMOS design.
• Input frequency range: 13MHz to 30MHz for 2.5V
13MHz to 30MHz for 3.3V
• Generates a 1X low EMI spread spectrum clock of
the input frequency.
• Frequency deviation: -1.25% @ 22MHz.
• Available in 6L-TSOP (6L-TSOT-23) packages.
Product Description
The ASM3P2872A is a versatile spread spectrum
frequency modulator designed specifically for a wide
range of clock frequencies. The ASM3P2872A reduces
electromagnetic interference (EMI) at the clock source,
allowing system wide reduction of EMI of all clock
dependent signals. The ASM3P2872A allows significant
system cost savings by reducing the number of circuit
board layers, ferrite beads and shielding that are
traditionally required to pass EMI regulations.
The ASM3P2872A uses the most efficient and optimized
modulation profile approved by the FCC and is
implemented by using a proprietary all digital method.
The ASM3P2872A 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.’
Applications
The ASM3P2872A is targeted towards all portable
devices like MP3 players, Notebooks and digital still
cameras.
Key Specifications
Description Specification
Supply voltages VDD = 3.3V /2.5V
Cycle-to-Cycle Jitter ±200pS (Typ)
Output Duty Cycle 45/55% (worst case)
Modulation Rate Equation F
IN
/640
Frequency Deviation -1.25% @ 22MHz
Block Diagram
VSS
Mo
dOUT
VDD
XIN
Frequency
Divider
Feedback
Divider
Modulation
Phase
Detector
Loop
Filter
VCO
Output
Divider
PLL
Crystal
Oscillator
XOUT
REFOUT
