ASM3P2474A Datasheet, PDF (1/10 Pages) Alliance Semiconductor Corporation – Low Power Peak EMI Reducing Solution

October 2005
ASM3P2474A
rev 1.0
Low Power Peak EMI Reducing Solution
Features
ƒ Generates an EMI optimized clock signal at the
output.
ƒ Integrated loop filter components.
ƒ Operates with a 3.3V Supply.
ƒ Operating current less than 6mA.
ƒ Low power CMOS design.
ƒ Input frequency range : 13MHz to 30MHz
ƒ Generates a 1X and 2X low EMI spread spectrum
clock of the input frequency.
ƒ Output Frequency Selection through FSEL pin
ƒ Frequency deviation : -1.5% (Typ) @25MHz
: -1.5% (Typ) @50MHz
ƒ Available in 6-pin TSOT-23, 8-pin SOIC and 8-pin
TSSOP packages.
Product Description
The ASM3P2474A is a versatile spread spectrum
frequency modulator designed specifically for a wide
range of clock frequencies. The ASM3P2474A reduces
electromagnetic interference (EMI) at the clock source,
allowing system wide reduction of EMI of all clock
dependent signals. The ASM3P2474A 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 ASM3P2474A uses the most efficient and optimized
modulation profile approved by the FCC and is
implemented by using a proprietary all digital method.
The ASM3P2474A 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 ASM3P2474A is targeted towards all portable
devices with very low power requirements like MP3
players and digital still cameras.
Key Specifications
Description
Supply voltages
Cycle-to-Cycle Jitter
Output Duty Cycle
Modulation Rate Equation
Frequency
Deviation
FSEL=0
FSEL=1
Specification
VDD = 3.3V ± 0.3V
200pS (Typ)
45/55% (worst case)
F_IN/640
-1.5% (Typ) @ 50MHz
-1.5% (Typ) @ 25MHz
Block Diagram
VDD
FSEL
XIN/CLKIN
XOUT
Crystal
Oscillator
Frequency
Divider
Feedback
Divider
Modulation
Phase
Detector
Loop
Filter
PLL
VCO
Output
Divider
ModOUT
VSS
Alliance Semiconductor
2575 Augustine Drive • Santa Clara, CA • Tel: [phone] • Fax: [phone] • www.alsc.com
Notice: The information in this document is subject to change without notice.