September 2004
rev 1.0
Peak Reducing EMI Solution
Features
•
Generates an EMI optimized clocking
signal at the output.
•
Selectable output frequency range.
•
Single 1.25% or 2.4% down spread
output.
•
Integrated loop filter components.
•
Operates with a 3.3V supply.
•
Low-power CMOS design.
•
Available in 8-pin SOIC and 8-pin
TSSOP packages.
Product Description
The ASM3P2180A is a versatile Spread
Spectrum frequency modulator designed
specifically for a wide range of clock
frequencies.
The
ASM3P2180A
reduces
electromagnetic interference (EMI) at the clock
source, allowing system wide reduction of EMI
of down stream clock and data dependent
signals. The ASM3P2180A allows significant
system cost savings by reducing the number of
circuit board layers and shielding that are
traditionally required to pass EMI regulations.
The ASM3P2180A modulates the output of a
single 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
Simplified Block Diagram
ASM3P2180A
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 ASM3P2180A uses the most efficient and
optimized modulation profile approved by the
FCC and is implemented by using a proprietary
all-digital method.
Applications
The ASM3P2180A is targeted towards notebook
LCD displays, other displays using an LVDS
interface, PC peripheral devices and embedded
systems.
Key Specifications
Description
Supply voltages
Frequency
range
FS1=0
FS1=1
Specification
V
DD
= 3.3V ± 5%
6 MHz
≤
Fin
≤10
MHz
18 MHz
≤
Fin
≤
30 MHz
325 pS (max)
-1.25% or –2.4%
45/55% (worst case)
5ns (maximum)
Cycle-to-cycle jitter
Selectable spread percentage
Output duty cycle
Output rise and fall time
3.3V
X1
ASM3P2180A
X2
Spread spectrum output
(EMI suppressed)
Alliance Semiconductor
2595, Augustine Drive
•
Santa Clara
•
CA 95054
•
Tel 408 855 4900
•
Fax 408 855 4999
•
www.alsc.com
Notice: The information in this document is subject to change without notice.
September 2004
rev 1.0
Pin Diagram
ASM3P2180A
CLKIN / X1
NC / X2
GND
SS%
1
2
8
7
NC
FS1
VDD
CLKOUT
ASM3P2180A
3
4
6
5
Modulation Width Selection
SS%
0
1
Output
FIN
≥
FOUT
≥
FIN – 1.25%
FIN
≥
FOUT
≥
FIN – 2.4%
Frequency Range Selection
FS1
0
1
Modulation Rate
6
≤
FIN
≤10
18
≤
FIN
≤
30
Pin Description
Pin#
1
2
3
4
5
6
7
8
Pin Name
CLKIN / X1
NC / X2
GND
SS%
CLKOUT
VDD
FS1
NC
Type
I
O
P
I
O
P
I
-
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. Connection for an external crystal. If using an
external reference, this pin must be left unconnected.
Ground to entire chip.
Modulation width selection. When spread spectrum feature is turned
on, this pin is used to select the amount of variation and peak EMI
reduction that is desired on the output signal. Internal pull-up resistor.
Output modulated frequency. Copy of the un-modulated input clock.
Power supply for the entire chip (3.3V).
Frequency selection bit 1. This pin selects the frequency range of
operation. (Refer
to the Frequency Range Selection Table).
This pin
has an internal pull-up resistor.
No connect.
Peak Reducing EMI Solution
Notice: The information in this document is subject to change without notice.
2 of 7
September 2004
rev 1.0
Absolute Maximum Ratings
ASM3P2180A
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
Parameter
Input high voltage
Input low current (pull-up resistors on inputs SS%,
FS1)
Input high current
X
OUT
output low current (@ 0.4V, V
DD
= 3.3V)
X
OUT
output high current (@2.5V, V
DD
= 3.3V)
Output low voltage (V
DD
= 3.3V, I
OL
= 4mA)
Output high voltage (V
DD
= 3.3V, I
OH
= 4mA)
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 output impedance
Min
GND – 0.3
2.0
-
-
-
-
-
2.5
8
-
2.8
-
-
Typ
-
-
-
-
3
4
-
-
21
0.8
3.3
0.18
50
Max
0.8
V
DD
+ 0.3
-27
18
-
-
0.4
-
35
-
3.7
-
-
Unit
V
V
µA
µA
mA
mA
V
V
mA
µA
V
mS
Ω
AC Electrical Characteristics
Symbol
CLKIN
CLKOUT
t
LH
*
t
HL
*
t
JC
Input frequency
Output frequency
Parameter
Min
6
6
1.2
0.8
-
45
Typ
-
-
1.3
0.9
-
50
Max
30
30
1.4
1.0
325
55
Unit
MHz
MHz
nS
nS
pS
%
Output rise time (measured at 0.8V to 2.0V)
Output fall time (measured at 2.0V to 0.8V)
Jitter (cycle to cycle)
t
D
Output duty cycle
*t
LH
and t
HL
are measured into a capacitive load of 15pF
Peak Reducing EMI Solution
Notice: The information in this document is subject to change without notice.
3 of 7
September 2004
rev 1.0
Package Information:
8-Pin SOIC Package
ASM3P2180A
E
H
D
A2
A
θ
e
B
A
1
C
L
Symbol Dimensions in inches
Min
A
A1
A2
B
C
D
E
e
H
L
0.057
0.004
0.053
0.012
0.004
0.186
0.148
Max
0.071
0.010
0.069
0.020
0.01
0.202
0.164
Dimensions in millimeters
Min
1.45
0.10
1.35
0.31
0.10
4.72
3.75
Max
1.80
0.25
1.75
0.51
0.25
5.12
4.15
1.27 BSC
5.70
0.30
0°
6.30
0.70
8°
0.050 BSC
0.224
0.012
0°
0.248
0.028
8°
D
Peak Reducing EMI Solution
4 of 7
Notice: The information in this document is subject to change without notice.
September 2004
rev 1.0
ASM3P2180A
8-Pin TSSOP Package
H
E
D
A2
A
θ
e
B
A1
L
C
Symbol
A
A1
A2
B
C
D
E
e
H
L
θ
Dimensions
in inches
Min
Max
0.047
0.002
0.031
0.007
0.004
0.114
0.169
0.006
0.041
0.012
0.008
0.122
0.177
Dimensions
in millimeters
Min
Max
1.10
0.05
0.80
0.19
0.09
2.90
4.30
0.15
1.05
0.30
0.20
3.10
4.50
0.026 BSC
0.244
0.018
0°
0.260
0.030
8°
0.65 BSC
6.20
0.45
0°
6.60
0.75
8°
Peak Reducing EMI Solution
Notice: The information in this document is subject to change without notice.
5 of 7
微控制器 MCU
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
