July 2005
rev 0.3
Peak EMI Reducing Solution
Features
FCC approved method of EMI attenuation.
Generates a 1X low EMI spread spectrum clock of
the input frequency.
Input frequency range: 25MHz to 45MHz.
Internal loop filter minimizes external components
and board space.
Frequency deviation: - 1.3%( Typ) @32MHz.
Low cycle-to-cycle jitter.
5.0V ± 5% operating voltage range.
TTL or CMOS compatible outputs.
Available in 8-pin SOIC and TSSOP Packages.
ASM3P2108A
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 ASM3P2108A uses the most efficient and optimized
modulation profile approved by the FCC and is
implemented in a proprietary all digital method.
The ASM3P2108A 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 ASM3P2108A is a versatile spread spectrum
frequency modulator designed specifically for input clock
frequencies from 25MHz to 45MHz. The ASM3P2108A
can generate an EMI reduced clock from crystal, ceramic
resonator, or system clock.
The ASM3P2108A reduces electromagnetic interference
(EMI) at the clock source, allowing system wide reduction
of EMI of
down stream clock and data dependent
signals. The ASM3P2108A allows significant system cost
Applications
The ASM3P2108A is targeted towards EMI management
for high speed digital applications such as PC peripheral
devices, consumer electronics and embedded controller
systems.
Block Diagram
V
DD
Modulation
XIN
Crystal
Oscillator
XOUT
Frequency
Divider
Feedback
Divider
Phase
Detector
Loop
Filter
PLL
VCO
Output
Divider
CLOCKOUT
GND
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.
July 2005
rev 0.3
Pin Configuration
ASM3P2108A
XIN / CLKIN
XOUT
GND
NC
1
2
3
4
8
NC
NC
VDD
CLOCKOUT
ASM3P2108A
7
6
5
Pin Description
Pin#
1
2
3
4
5
6
7
8
Pin Name
XIN/CLKIN
XOUT
GND
NC
CLOCKOUT
VDD
NC
NC
Type
I
O
P
-
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. If using an external reference, this pin must be left unconnected.
Ground to entire chip.
No connect.
Spread spectrum low EMI output.
Power supply for the entire chip (5V).
No connect.
No connect.
Peak EMI Reducing Solution
Notice: The information in this document is subject to change without notice.
2 of 7
July 2005
rev 0.3
Absolute Maximum Ratings
Symbol
V
DD
, V
IN
T
STG
T
A
T
s
T
J
T
DV
Storage temperature
Operating temperature
Max. Soldering Temperature (10 sec)
Junction Temperature
Static Discharge Voltage
(As per JEDEC STD22- A114-B)
ASM3P2108A
Parameter
Voltage on any pin with respect to Ground
Rating
-0.5 to +7.0
-65 to +125
0 to 70
260
150
2
Unit
V
°C
°C
°C
°C
KV
Note: These are stress ratings only and are not implied for functional use. Exposure to absolute maximum ratings for prolonged periods of time 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
X
OUT
output low current (@ 0.4, V
DD
= 5V)
X
OUT
output high current (@2.5V, V
DD
= 5V)
Output low voltage (V
DD
= 5V, I
OL
= 20mA)
Output high voltage (V
DD
= 5V, I
OH
= 20mA)
Dynamic supply current normal mode
(5V, 32MHz and 15pF 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
-
-
4.75
-
-
Typ
-
-
44
66
3
3
-
-
40
40
5.0
0.18
50
Max
0.8
V
DD
+ 0.3
-
-
-
-
0.4
-
-
-
5.25
-
-
Unit
V
V
µA
µA
mA
mA
V
V
mA
µA
V
mS
Ω
AC Electrical Characteristics
Symbol
f
IN
MODOUT
f
d
t
LH
*
t
HL
*
t
JC
t
D
Input frequency
Output frequency
Frequency Deviation
Input Frequency =25MHz
Input Frequency =45MHz
Output rise time (measured at 0.8V to 2.0V)
Output fall time (measured at 2.0V to 0.8V)
Jitter (cycle to cycle)
Output duty cycle
Parameter
Min
25
25
-
-
-
-
-
45
Typ
-
-
-1.98
-0.60
440
300
-
50
Max
45
45
-
-
-
-
360
55
Unit
MHz
MHz
%
pS
pS
pS
%
* V
DD
= +5V, Input Frequency = 32MHz, t
LH
and t
HL
are measured into a capacitive load of 15pF
Peak EMI Reducing Solution
Notice: The information in this document is subject to change without notice.
3 of 7
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