August 2005
ASM3P2579A
rev 1.0
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.
Low Power Peak EMI Reducing Solution
Features
Generates an EMI optimized clock signal at the
output.
Integrated loop filter components.
Operates
with
a
3.3 / 2.5V Supply.
Operating current less than 4mA.
Low power CMOS design.
Input frequency range: 12MHz to 30MHz for 2.5V
: 12MHz to 30MHz for 3.3V
Generates a 1X low EMI spread spectrum clock of
the input frequency.
Spread Spectrum Enable Control.
Frequency deviation: 1% @ 24MHz
Available in 6 pin TSOT-23, 8 pin SOIC and 8 pin
TSSOP Packages.
Product Description
The ASM3P2579A is a versatile spread spectrum
frequency modulator designed specifically for a wide
range of clock frequencies. The ASM3P2579A reduces
electromagnetic interference (EMI) at the clock source,
allowing system wide reduction of EMI of all clock
dependent signals. The ASM3P2579A allows significant
system cost savings by reducing the number of circuit
board layers ferrite beads, shielding that are traditionally
required to pass EMI regulations.
The ASM3P2579A uses the most efficient and optimized
modulation profile approved by the FCC and is
implemented by using a proprietary all digital method.
The ASM3P2579A 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 ASM3P2579A is targeted towards all portable
devices with very low power requirements like MP3
players and digital still cameras.
Key Specifications
Description
Specification
Supply voltages
VDD = 3.3V/2.5V
Cycle-to-Cycle Jitter
200pS (Max)
Output Duty Cycle
45/55% (worst case)
Modulation Rate Equation
F
IN
/640
Frequency Deviation
1% @ 24MHz
Block Diagram
ModOUT
VSS
XIN
Frequency
Divider
Feedback
Divider
Modulation
Phase
Detector
Loop
Filter
VCO
Output
Divider
PLL
Crystal
Oscillator
XOUT
SSON
VDD
August 2005
ASM3P2579A
rev 1.0
Low Power Peak EMI Reducing Solution
2 of 12
Notice: The information in this document is subject to change without notice.
VDD
ModOUT
XIN/CLKIN
XOUT
1
2
3
4
5
6
ASM3P2579A
SSON
VSS
Pin Configuration (6-pin TSOT-23 Package)
Pin Description
Pin# Pin Name Type
Description
1 SSON I
When SSON is HIGH, the spread spectrum is enabled and when LOW, it turns off the
spread spectrum. Connect the pin to ground When Spread Spectrum feature is not
required.
2
XOUT
O
Crystal connection. If using an external reference, this pin must be left unconnected.
3 XIN/CLKIN I
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.
4
VDD
P
Power supply for the entire chip
5
ModOUT
O
Spread spectrum clock output.
6 VSS P
Ground
connection.
August 2005
ASM3P2579A
rev 1.0
Low Power Peak EMI Reducing Solution
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Notice: The information in this document is subject to change without notice.
XIN/CLKIN
VSS
ModOUT
NC
XOUT
1
2
3
4
5
6
7
8
ASM3P2579A
SSON
NC
VDD
Pin Configuration (8-pin SOIC and TSSOP Packages)
Pin Description
Pin# Pin Name Type
Description
1 XIN/CLKIN I
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.
2
XOUT
O
Crystal connection. If using an external reference, this pin must be left unconnected.
3
I
When SSON is HIGH, the spread spectrum is enabled and when LOW, it turns off the
spread spectrum. Connect the pin to ground When Spread Spectrum feature is not
required.
4 NC -
No
connect.
5 VSS P
Ground
connection.
6
ModOUT
O
Spread spectrum clock output.
7 NC -
No
connect.
8
VDD
P
Power supply for the entire chip
Modulation Profile
Specifications
Description
Specification
Frequency Range
12MHz < CLKIN < 30MHz
Modulation Equation
F
IN
/640
Frequency Deviation
1% @ 24MHz
SSON
August 2005
ASM3P2579A
rev 1.0
Low Power Peak EMI Reducing Solution
4 of 12
Notice: The information in this document is subject to change without notice.
Absolute Maximum Ratings
Symbol
Parameter
Rating
Unit
VDD, V
IN
Voltage on any pin with respect to Ground
-0.5 to +7.0
V
T
STG
Storage temperature
-65 to +125
C
T
A
Operating temperature
0 to 70
C
T
s
Max. Soldering Temperature (10 sec)
260
C
T
J
Junction
Temperature
150
C
T
DV
Static Discharge Voltage
(As per JEDEC STD22- A114-B)
2 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 for 2.5V Supply
(Test condition: All parameters are measured at room temperature (+25C) unless otherwise stated)
Symbol
Parameter
Min
Typ
Max
Unit
V
IL
Input low voltage
VSS - 0.3
-
0.8
V
V
IH
Input high voltage
2.0
-
VDD + 0.3
V
I
IL
Input low current
-
-
-35
A
I
IH
Input high current
-
-
35
A
I
XOL
XOUT output low current (@0.5V, VDD=2.5V)
-
3
-
mA
I
XOH
XOUT output high current (@1.8V, VDD=2.5V)
-
3
-
mA
V
OL
Output low voltage (VDD = 2.5 V, I
OL
= 8mA)
-
-
0.6
V
V
OH
Output high voltage (VDD = 2.5 V, I
OH
=
8mA)
1.8 - - V
I
DD
Static supply current *
-
1.1
-
mA
I
CC
Dynamic supply current (2.5V, 24MHz and no load)
-
3.5
-
mA
VDD Operating
Voltage
2.375 2.5 2.625 V
t
ON
Power-up time (first locked cycle after power-up)
-
-
5
mS
Z
OUT
Output
impedance
-
50
-
* XIN/CLKIN is made low.
AC Electrical Characteristics for 2.5V Supply
Symbol
Parameter
Min
Typ
Max
Unit
CLKIN
Input
frequency
12 - 30
MHz
ModOUT
Output
frequency
12 - 30
MHz
Input Frequency = 12MHz
-
-
1.65
f
d
Frequency
Deviation
Input Frequency = 30MHz
-
-
0.80
%
t
LH
*
Output rise time (measured from 0.7V to 1.7V)
0.7
1.5
1.9
nS
t
HL
*
Output fall time (measured from 1.7V to 0.7V)
0.4
1.0
1.1
nS
t
JC
Jitter (cycle to cycle)
-
-
200
pS
t
D
Output duty cycle
45
50
55
%
* t
LH
and t
HL
are measured into a capacitive load of 15pF
August 2005
ASM3P2579A
rev 1.0
Low Power Peak EMI Reducing Solution
5 of 12
Notice: The information in this document is subject to change without notice.
DC Electrical Characteristics for 3.3V Supply
(Test condition: All parameters are measured at room temperature (+25C) unless otherwise stated)
Symbol
Parameter
Min
Typ
Max
Unit
V
IL
Input low voltage
VSS - 0.3
-
0.8
V
V
IH
Input high voltage
2.0
-
VDD + 0.3
V
I
IL
Input low current
-
-
-35
A
I
IH
Input high current
-
-
35
A
I
XOL
XOUT output low current (@0.4V, VDD=3.3V)
-
3
-
mA
I
XOH
XOUT output high current (@2.5V, VDD=3.3V)
-
3
-
mA
V
OL
Output low voltage (VDD = 3.3 V, I
OL
= 8mA)
-
-
0.4
V
V
OH
Output high voltage (VDD = 3.3 V, I
OH
=
8mA)
2.5 - - V
I
DD
Static supply current*
-
1.2
-
mA
I
CC
Dynamic supply current (3.3V, 24MHz and no load)
-
4.0
-
mA
VDD Operating
Voltage
2.7 3.3 3.6 V
t
ON
Power-up time (first locked cycle after power-up)
-
-
5
mS
Z
OUT
Output
impedance
-
45
-
* XIN/CLKIN is made low.
AC Electrical Characteristics for 3.3V Supply
Symbol
Parameter
Min
Typ
Max
Unit
CLKIN Input
frequency
12 - 30
MHz
ModOUT Output
frequency
12
-
30 MHz
Input Frequency = 12MHz
-
-
1.65
f
d
Frequency
Deviation
Input Frequency = 30MHz
-
-
0.80
%
t
LH
*
Output rise time (measured from 0.8 to 2.0V)
0.5
1.4
1.7
nS
t
HL
*
Output fall time (measured at 2.0V to 0.8V)
0.4
1.0
1.2
nS
t
JC
Jitter (cycle to cycle)
-
-
200
pS
t
D
Output duty cycle
45
50
55
%
*t
LH
and t
HL
are measured into a capacitive load of 15pF
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