November 2003
rev 1.1
ASM3P2185B
EMI Reduction IC
Features
FCC approved method of EMI attenuation.
Provides up to 15dB EMI reduction.
Generates a 1X low EMI spread spectrum clock of
the input frequency.
Input frequency range: 25MHz to 50 MHz.
Internal loop filter minimizes external components
and board space.
Down Spread and Center Spread.
2 spread frequency deviation selections: -1.25%
and ± 0.8%.
Low inherent cycle-to-cycle jitter.
3.3V operating voltage range.
TTL or CMOS compatible inputs and outputs.
Low power CMOS design.
Supports notebook VGA and other LCD timing
controller applications.
Products are available for industrial temperature
range.
Available in 8-pin SOIC and TSSOP.
The ASM3P2185B reduces electromagnetic interference
(EMI) at the clock source, allowing system wide EMI
reduction for all the down stream clocks and data
dependent signals. The ASM3P2185B 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 ASM3P2185B uses the most efficient and optimized
modulation profile approved by the FCC and is
implemented in a proprietary all digital method.
The ASM3P2185B 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’.
Product Description
The ASM3P2185B is a versatile spread spectrum
frequency modulator designed specifically for a wide
range of input clock frequencies from 25MHz to 50MHz.
The ASM3P2185B can generate an EMI reduced clock
from an OSC or a system generated clock.
Applications
The ASM3P2185B is targeted towards EMI management
for memory and LVDS interfaces in mobile graphic
chipsets and high-speed digital applications such as PC
peripheral devices, consumer electronics, and embedded
controller systems.
Block Diagram
SS%
VDD
Modulation
XIN
Crystal
Oscillator
XOUT
Feedback
Divider
Frequenc
y
Phase
Detector
Loop
Filter
PLL
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.
November 2003
rev 1.1
Pin Configuration
XIN
XOUT
GND
SS%
1
2
8
7
ASM3P2185B
NC
NC
VDD
ModOUT
ASM3P2185B
3
6
5
4
Pin Description
Pin#
1
2
3
4
5
6
7
8
Pin Name
XIN
XOUT
GND
SS%
ModOUT
VDD
NC
NC
Type
I
I
P
I
O
P
Description
Crystal connection or external reference frequency input. This pin has dual
functions. It can be connected to either an external crystal or an external
reference clock.
Crystal connection. Input connection for an external crystal. If using an
external reference, this pin must be left unconnected.
Ground to entire chip.
Spread range select. Digital logic input used to select frequency deviation
(Refer
Spread Deviation Table).
This pin has an internal pull-up resistor.
Spread spectrum low EMI output.
Power supply for the entire chip (3.3V).
No Connect.
No Connect.
Spread Deviation Selection Table
SS% (pin 4)
0
1
Spread Deviation (%)
- 1.25
± 0.8%
EMI Reduction IC
Notice: The information in this document is subject to change without notice.
2 of 7
November 2003
rev 1.1
ASM3P2185B
Absolute Maximum Ratings
Symbol
V
DD
, V
IN
T
STG
T
A
Parameter
Voltage on any pin with respect to GND
Storage temperature
Operating temperature
Rating
-0.5 to + 7.0
-65 to +125
Unit
V
°C
0 to 70
°C
Note: These are stress ratings only and functional operation is not implied. Exposure to absolute maximum
ratings for extended periods may affect device reliability.
DC Electrical Characteristics
Symbol
V
IL
V
IH
I
IL
I
IH
I
XOL
I
XOH
V
OL
V
OH
I
CC
I
DD
V
DD
t
ON
Z
OUT
Input low voltage
Input high voltage
Input low current
Input high current
XOUT Output low current (@ 0.4V, V
DD
= 3.3V)
XOUT Output high current (@ 2.5V, V
DD
= 3.3V)
Output low voltage (V
DD
= 3.3V, I
OL
= 20mA)
Output high voltage (V
DD
= 3.3V, I
OH
= 20mA)
Dynamic supply current
Normal mode (3.3V and 10pF loading)
Static supply current
Standby mode
Operating voltage
Power up time (first locked clock cycle after power up)
Clock out impedance
Parameter
Min
GND – 0.3
2.0
-
-
-
-
-
2.5
8.46
Typ
-
-
-
-
TBD
TBD
-
-
12
0.6
2.7
-
-
3.3
0.18
50
3.7
-
-
Max
0.8
V
DD
+ 0.3
-35
35
-
-
0.4
-
17.78
Unit
V
V
µA
µA
mA
mA
V
V
mA
mA
V
mS
Ω
EMI Reduction IC
Notice: The information in this document is subject to change without notice.
3 of 7
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