Document
August 2005
www.DataSheet4U.com rev 1.0
ASM3P2579A
Low Power Peak EMI Reducing Solution
Features
Generates an EMI optimized clock signal at the output. Integrated loop filter components. Operates with a 3.3 / 2.5V Supply. Operating current less than 4mA. Low power CMOS design. Input frequency range: 12MHz to 30MHz for 2.5V : 12MHz to 30MHz for 3.3V Generates a 1X low EMI spread spectrum clock of the input frequency. Spread Spectrum Enable Control. Frequency deviation: ±1% @ 24MHz Available in 6 pin TSOT-23, 8 pin SOIC and 8 pin TSSOP Packages.
The ASM3P2579A uses the most efficient and optimized modulation profile approved by the FCC and is implemented by using a proprietary all digital method. The ASM3P2579A 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 ASM3P2579A is targeted towards all portable devices with very low power requirements like MP3 players and digital still cameras.
Product Description
The ASM3P2579A is a versatile spread spectrum frequency modulator designed specifically for a wide range of clock frequencies. The ASM3P2579A reduces electromagnetic interference (EMI) at the clock source, allowing system wide reduction of EMI of all clock dependent signals. The ASM3P2579A allows significant system cost savings by reducing the number of circuit board layers ferrite beads, shielding that are traditionally required to pass EMI regulations.
Key Specifications Description
Supply voltages Cycle-to-Cycle Jitter Output Duty Cycle Modulation Rate Equation Frequency Deviation
Specification
VDD = 3.3V/2.5V 200pS (Max) 45/55% (worst case) FIN/640 ±1% @ 24MHz
Block Diagram
VDD SSON
XIN Crystal Oscillator Frequency Divider Feedback Divider
Modulation
PLL
XOUT
Phase Detector
Loop Filter
VCO
Output Divider ModOUT
VSS
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.
August 2005
www.DataSheet4U.com rev 1.0
ASM3P2579A
Pin Configuration (6-pin TSOT-23 Package)
SSON XOUT XIN/CLKIN
1 2 3
6
VSS ModOUT VDD
ASM3P2579A
5 4
Pin Description Pin#
1 2 3 4 5 6
Pin Name
SSON XOUT XIN/CLKIN VDD ModOUT VSS
Type
I O I P O P
Description
When SSON is HIGH, the spread spectrum is enabled and when LOW, it turns off the spread spectrum. Connect the pin to ground When Spread Spectrum feature is not required. Crystal connection. If using an external reference, this pin must be left unconnected. Crystal connection or external reference frequency input. This pin has dual functions. It can be connected either to .