ASM3P2508A Datasheet, PDF (1/9 Pages) Alliance Semiconductor Corporation – Peak EMI Reducing Solution

February 2007
ASM3P2508A
rev 1.4
Peak EMI Reducing Solution
Features
• Generates an EMI optimized clocking signal at
output.
• Input frequency – 14.31818MHz.
• Frequency outputs:
• 120MHz (modulated) - default.
• 72MHz (modulated) or 48MHz (modulated)
selectable via I2C
• ± 1% Centre spread.
• Modulation rate: 40KHz.
• Byte Write via I2C
• Supply voltage range 3.3V ± 0.3V.
• Available in 8-pin SOIC Package.
• Available in Commercial and Industrial
Temperature ranges.
Product Description
The ASM3P2508A is a versatile spread spectrum
frequency modulator. The ASM3P2508A reduces
electromagnetic interference (EMI) at the clock source.
The ASM3P2508A allows significant system cost savings
by reducing the number of circuit board layers and
shielding that are required to pass EMI regulations. The
ASM3P2508A modulates the output of PLL in order to
spread the bandwidth of a synthesized clock, thereby
decreasing 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 clock generators. Lowering EMI by increasing a
signal’s bandwidth is called spread spectrum clock
generation.
The ASM3P2508A has a feature to power down the
72MHz/48MHz output by writing data into specific
registers in the device via I2C. By writing a ‘0’ into bit 1 of
Byte 0, the PLL block generating 72MHz / 48MHz can be
powered down. Writing ‘0’ into bit ‘7’ of Byte 1 selects an
output of 72 MHz on FOUT2CLK while a ‘1’ at the same
location selects a 48 MHz clock output. However, the I2C
block, crystal oscillator, and the PLL block generating
120MHz would be always running.
Block Diagram
V_DD
XIN
XOUT
SCL
SDA
Crystal
Oscillator
I2C
Interface
PLL 1
PLL 2
FOUT1CLK
(120MHz)
FOUT2CLK
(72 MHz / 48MHz)
V_SS
PulseCore Semiconductor Corporation
1715 S. Bascom Ave Suite 200, Campbell, CA 95008 • Tel: [phone] • Fax: [phone]
www.pulsecoresemi.com
Notice: The information in this document is subject to change without notice.