The ASM3P2474A uses the most efficient and optimized
modulation profile approved by the FCC and is
implemented by using a proprietary all digital method.
The ASM3P2474A 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 ASM3P2474A is targeted towards all portable
devices with very low power requirements like MP3
players and digital still cameras.
Product Description
The ASM3P2474A is a versatile spread spectrum
frequency modulator designed specifically for a wide
range of clock frequencies. The ASM3P2474A reduces
electromagnetic interference (EMI) at the clock source,
allowing system wide reduction of EMI of
all clock
dependent signals. The ASM3P2474A allows significant
system cost savings by reducing the number of circuit
board layers, ferrite beads and 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
FSEL=0
FSEL=1
Specification
VDD = 3.3V
±
0.3V
200pS (Typ)
45/55% (worst case)
F
IN
/640
-1.5% (Typ) @ 50MHz
-1.5% (Typ) @ 25MHz
FSEL
Block Diagram
VDD
Modulation
XIN/CLKIN
XOUT
Crystal
Oscillator
Frequency
Divider
Feedback
Divider
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.
October 2005
rev 1.0
Pin Configuration (6-pin TSOT- 23 Package)
ASM3P2474A
FSEL
XOUT
1
2
6
VSS
ASM3P2474A
5
4
ModOUT
VDD
XIN / CLKIN
3
Pin Description
Pin#
1
2
3
4
5
6
Pin Name
FSEL
XOUT
XIN / CLKIN
VDD
ModOUT
VSS
Type
I
O
I
P
O
P
Description
Selection Pin for 1X and 2X Output Frequency Options. Please refer the table
“Frequency Selection Options” for further details
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 an external crystal or an external reference clock.
Power supply for the entire chip.
Spread spectrum clock output.
Ground connection.
Pin Configuration (8-pin SOIC and TSSOP Packages)
XIN / CLKIN
XOUT
1
2
8
7
6
5
VDD
NC
ModOUT
VSS
ASM3P2474A
FSEL
3
NC
4
Pin Description
Pin#
1
2
3
4
5
6
7
8
Pin Name
XIN/CLKIN
XOUT
FSEL
NC
VSS
ModOUT
NC
VDD
Type
I
O
I
-
P
O
-
P
Description
Crystal connection or external reference frequency input. This pin has dual functions. It
can be connected either to an external crystal or an external reference clock.
Crystal connection. If using an external reference, this pin must be left unconnected.
Selection Pin for 1X and 2X Output Frequency Options. Please refer the table
“Frequency Selection Options” for further details
No connect.
Ground connection.
Spread spectrum clock output.
No connect.
Power supply for the entire chip.
Low Power Peak EMI Reducing Solution
Notice: The information in this document is subject to change without notice.
2 of 10
October 2005
rev 1.0
Modulation Profile
ASM3P2474A
Specifications
Description
Frequency Range
Modulation Equation
Frequency Deviation
FSEL=0
FSEL=1
Specification
13MHz < CLKIN < 30MHz
F
IN
/640
-1.5% (Typ) @ 50MHz
-1.5% (Typ) @ 25MHz
Frequency Selection Options
FSEL Pin
0
1
Input Frequency (MHz)
13-30
13-30
Output Frequency (MHz)
26-60
13-30
Absolute Maximum Ratings
Symbol
VDD, 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)
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.
Low Power Peak EMI Reducing Solution
Notice: The information in this document is subject to change without notice.
3 of 10
October 2005
rev 1.0
DC Electrical Characteristics
(Test condition: All parameters are measured at room temperature (+25°C) unless otherwise stated)
ASM3P2474A
Symbol
V
IL
V
IH
I
IL
I
IH
I
XOL
I
XOH
V
OL
V
OH
I
DD
I
CC
VDD
t
ON
Z
OUT
Input low voltage
Input high voltage
Input low current
Input high current
Parameter
Min
VSS - 0.3
2.0
-
-
-
-
-
2.5
-
-
3.0
-
-
Typ
-
-
-
-
3
3
-
-
1.6
4.0
3.3
-
45
Max
0.8
VDD + 0.3
-35
35
-
-
0.4
-
-
-
3.6
5
-
Unit
V
V
µA
µA
mA
mA
V
V
mA
mA
V
mS
Ω
XOUT output low current (@0.4V, VDD=3.3V)
XOUT output high current (@2.5V, VDD=3.3V)
Output low voltage (VDD = 3.3V, I
OL
= 8mA)
Output high voltage (VDD = 3.3V, I
OH
= 8mA)
Static supply current*
Dynamic supply current
(3.3V, 25MHz and no load and FSEL=1)
Operating voltage
Power-up time (first locked cycle after power-up)
Output impedance
* XIN /CLKIN pin is pulled low
AC Electrical Characteristics
Symbol
CLKIN
ModOUT
f
d
f
d
t
LH
*
t
HL
*
t
JC
t
D
Input frequency
Output frequency
Frequency Deviation
Frequency Deviation
FSEL=0
FSEL=1
Output Frequency =
Output Frequency =
Output Frequency =
Output Frequency =
Parameter
Min
13
26
13
-
-
-
-
0.4
0.3
-
45
Typ
-
-
-
-1.8
-0.9
-1.8
-0.9
0.85
0.7
200
50
Max
30
60
30
-
-
-
-
1.1
0.9
-
55
Unit
MHz
MHz
%
%
nS
nS
pS
%
13MHz
30MHz
26MHz
60MHz
Output rise time (measured from 0.8 to 2.0V)
Output fall time (measured at 2.0V to 0.8V)
Jitter (cycle to cycle)
Output duty cycle
*t
LH
and t
HL
are measured into a capacitive load of 15pF
Low Power Peak EMI Reducing Solution
Notice: The information in this document is subject to change without notice.
4 of 10
October 2005
rev 1.0
Typical Crystal Oscillator Circuit
ASM3P2474A
Crystal
R1 = 510Ω
C1 = 27 pF
C2 = 27 pF
Typical Crystal Specifications
Fundamental AT cut parallel resonant crystal
Nominal frequency
Frequency tolerance
Operating temperature range
Storage temperature
Load capacitance
Shunt capacitance
ESR
25MHz
± 50 ppm or better at 25°C
-25°C to +85°C
-40°C to +85°C
18pF
7pF maximum
25
Ω
Low Power Peak EMI Reducing Solution
Notice: The information in this document is subject to change without notice.
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