September 2005
ASM3P2779A
rev 3.0
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 : 13MHz to 30MHz for 2.5V.
: 13MHz to 30MHz for 3.3V.
Generates a 1X low EMI spread spectrum clock of
the input frequency.
Frequency deviation: 1% (Typ) @16MHz Input
Frequency.
Available in 6-pin TSOT-23, 8-pin SOIC and 8-pin
TSSOP packages.
Product Description
The ASM3P2779A is a versatile spread spectrum
frequency modulator designed specifically for a wide
range of clock frequencies. The ASM3P2779A reduces
electromagnetic interference (EMI) at the clock source,
allowing system wide reduction of EMI of all clock
dependent signals. The ASM3P2779A 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 ASM3P2779A uses the most efficient and optimized
modulation profile approved by the FCC and is
implemented by using a proprietary all digital method.
The ASM3P2779A 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 ASM3P2779A is targeted towards all portable
devices with very low power requirements like MP3
players and digital still cameras.
Key Specifications
Description
Specification
Supply voltages
V
DD
= 3.3V / 2.5V
Cycle-to-Cycle Jitter
200pS (Max)
Output Duty Cycle
45/55%
Modulation Rate Equation
F
IN
/640
Frequency Deviation
1% (Typ) @ 16MHz
Block Diagram
ModOUT
VSS
XIN/CLKIN
Frequency
Divider
Feedback
Divider
Modulation
Phase
Detector
Loop
Filter
VCO
Output
Divider
PLL
VDD
PD
Crystal
Oscillator
XOUT
September 2005
ASM3P2779A
rev 3.0
Low Power Peak EMI Reducing Solution
2 of 12
Notice: The information in this document is subject to change without notice.
Pin Configuration (6-pin TSOT- 23 Package)
Pin Description
Pin#
Pin Name
Type
Description
1
PD
I
Power-down control pin. Pull low to enable power-down mode. Connect to VDD if not
used.
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.
XOUT
1
2
3
4
5
6
ASM3P2779A
PD
XIN / CLKIN
VDD
ModOUT
VSS
September 2005
ASM3P2779A
rev 3.0
Low Power Peak EMI Reducing Solution
3 of 12
Notice: The information in this document is subject to change without notice.
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
PD
I
Power-down control pin. Pull low to enable power-down mode. Connect to VDD if not
used.
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
For 2.5V Supply
13MHz < CLKIN < 30MHz
Frequency Range
For 3.3V Supply
13MHz < CLKIN < 30MHz
Modulation Equation
F
IN
/640
Frequency Deviation
1% (Typ) @ 16MHz
VSS
ModOUT
XIN / CLKIN
NC
XOUT
1
2
3
4
5
6
7
8
ASM3P2779A
PD
NC
VDD
September 2005
ASM3P2779A
rev 3.0
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*
-
-
10
uA
I
CC
Dynamic supply current (2.5V, 16MHz and no load)
-
3.0
-
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 pin and PD pin are pulled low
** V
DD
and XIN/CLKIN input are stable, PD pin is made high from low.
AC Electrical Characteristics for 2.5V Supply
Symbol
Parameter
Min
Typ
Max
Unit
CLKIN Input
frequency
13
-
30
MHz
ModOUT Output
frequency
13
-
30
MHz
Input Frequency = 13MHz
-
1.15
-
f
d
Frequency
Deviation
Input Frequency = 30MHz
-
0.6
-
%
t
LH
*
Output rise time (measured from 0.7V to 1.7V)
0.7
1.4
1.8
nS
t
HL
*
Output fall time (measured from 1.7V to 0.7V)
0.4
0.9
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
September 2005
ASM3P2779A
rev 3.0
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*
-
-
10
uA
I
CC
Dynamic supply current (3.3V, 16MHz and no load)
-
3.5
-
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 pin and PD pin are pulled low
** V
DD
and XIN/CLKIN input are stable, PD pin is made high from low.
AC Electrical Characteristics for 3.3V Supply
Symbol
Parameter
Min
Typ
Max
Unit
CLKIN
Input
frequency
13 - 30
MHz
ModOUT Output
frequency
13
v
30
MHz
Input Frequency = 13MHz
-
1.15
-
f
d
Frequency
Deviation
Input Frequency = 30MHz
-
0.6
-
%
t
LH
*
Output rise time (measured from 0.8 to 2.0V)
0.5
1.1
1.3
nS
t
HL
*
Output fall time (measured at 2.0V to 0.8V)
0.3
0.8
0.9
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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