The ASM3P2780A uses the most efficient and optimized
modulation profile approved by the FCC and is
implemented by using a proprietary all digital method.
The ASM3P2780A 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 ASM3P2780A is targeted towards all portable
devices with very low power requirements like MP3
players and digital still cameras.
Product Description
The ASM3P2780A is a versatile spread spectrum
frequency modulator designed specifically for a wide
range of clock frequencies. The ASM3P2780A reduces
electromagnetic interference (EMI) at the clock source,
allowing system wide reduction of EMI of
all clock
dependent signals. The ASM3P2780A allows significant
system cost savings by reducing the number of circuit
board layers ferrite beads, 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
Specification
V
DD
= 3.3V / 2.5V
200pS (Max)
45/55%
F
IN
/1280
±0.75 (Typ) @ 46MHz
Block Diagram
V
DD
PD
Modulation
XIN/CLKIN
XOUT
Crystal
Oscillator
Frequency
Divider
Feedback
Divider
Phase
Detector
Loop
Filter
PLL
VCO
Output
Divider
ModOUT
V
SS
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.
September 2005
rev 1.5
Pin Configuration (6-pin TSOT- 23 Package)
ASM3P2780A
PD
1
XOUT
2
XIN / CLKIN
3
6
V
SS
ModOUT
V
DD
ASM3P2780A
5
4
Pin Description
Pin#
1
2
3
4
5
6
Pin Name
PD
XOUT
XIN / CLKIN
V
DD
ModOUT
V
SS
Type
I
O
I
P
O
P
Description
Power-down control pin. Pull low to enable power-down mode. Connect to V
DD
if not
used.
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.
Low Power Peak EMI Reducing Solution
Notice: The information in this document is subject to change without notice.
2 of 12
September 2005
rev 1.5
Pin Configuration (8-pin SOIC and TSSOP Packages)
ASM3P2780A
XIN / CLKIN
1
XOUT
2
PD
NC
3
4
8
7
6
5
V
DD
NC
ModOUT
V
SS
ASM3P2780A
Pin Description
Pin#
1
2
3
4
5
6
7
8
Pin Name
XIN/CLKIN
XOUT
PD
NC
V
SS
ModOUT
NC
V
DD
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.
Power-down control pin. Pull low to enable power-down mode. Connect to VDD if not
used.
No connect.
Ground connection.
Spread spectrum clock output.
No connect.
Power supply for the entire chip.
Modulation Profile
Specifications
Description
Frequency Range
For 2.5V Supply
For 3.3V Supply
Specification
30MHz < CLKIN < 50MHz
F
IN
/1280
±0.75% (Typ) @ 46MHz
Modulation Equation
Frequency Deviation
Low Power Peak EMI Reducing Solution
Notice: The information in this document is subject to change without notice.
3 of 12
September 2005
rev 1.5
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)
ASM3P2780A
Parameter
Rating
-0.5 to +7.0
-65 to +125
0 to 70
260
150
2
Unit
V
°C
°C
°C
°C
KV
Voltage on any pin with respect to Ground
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 (+25°C) unless otherwise stated)
Symbol
V
IL
V
IH
I
IL
I
IH
I
XOL
I
XOH
V
OL
V
OH
I
DD
I
CC
V
DD
t
ON
Z
OUT
Input low voltage
Input high voltage
Input low current
Input high current
Parameter
Min
V
SS
- 0.3
2.0
-
-
-
-
-
1.8
-
-
2.375
-
-
Typ
-
-
-
-
3
3
-
-
-
4.0
2.5
-
50
Max
0.8
V
DD
+ 0.3
-35
35
-
-
0.6
-
10
-
2.625
5
-
Unit
V
V
µA
µA
mA
mA
V
V
uA
mA
V
mS
Ω
XOUT output low current (@0.6V, V
DD
=2.5V)
XOUT output high current (@1.8V, V
DD
=2.5V)
Output low voltage (V
DD
= 2.5 V, I
OL
= 8mA)
Output high voltage (V
DD
= 2.5 V, I
OH
= 8mA)
Static supply current*
Dynamic supply current (2.5V, 46MHz and no load)
Operating Voltage
Power-up time (first locked cycle after power-up)**
Output impedance
* 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
CLKIN
ModOUT
f
d
t
LH
*
t
HL
*
t
JC
t
D
Input frequency
Output frequency
Frequency Deviation
Input Frequency = 30MHz
Input Frequency = 50MHz
Output rise time (measured from 0.7V to 1.7V)
Output fall time (measured from 1.7V to 0.7V)
Jitter (cycle to cycle)
Output duty cycle
Min
30
30
-
-
0.7
0.4
-
45
Typ
-
-
± 1.10
± 0.65
1.3
0.8
-
50
Max
50
50
-
-
1.6
1.0
200
55
Unit
MHz
MHz
%
nS
nS
pS
%
* 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 12
September 2005
rev 1.5
DC Electrical Characteristics for 3.3V Supply
(Test condition: All parameters are measured at room temperature (+ 25°C) unless otherwise stated)
ASM3P2780A
Symbol
V
IL
V
IH
I
IL
I
IH
I
XOL
I
XOH
V
OL
V
OH
I
DD
I
CC
V
DD
t
ON
Z
OUT
Input low voltage
Input high voltage
Input low current
Input high current
Parameter
Min
V
SS
- 0.3
2.0
-
-
-
-
-
2.5
-
-
2.7
-
-
Typ
-
-
-
-
3
3
-
-
-
5.0
3.3
-
45
Max
0.8
V
DD
+ 0.3
-35
35
-
-
0.4
-
10
-
3.6
5
-
Unit
V
V
µA
µA
mA
mA
V
V
uA
mA
V
mS
Ω
XOUT output low current (@0.4V, V
DD
=3.3V)
XOUT output high current (@2.5V, V
DD
=3.3V)
Output low voltage (V
DD
= 3.3 V, I
OL
= 8mA)
Output high voltage (V
DD
= 3.3 V, I
OH
= 8mA)
Static supply current*
Dynamic supply current (3.3V, 46MHz and no load)
Operating Voltage
Power-up time (first locked cycle after power-up)**
Output impedance
* 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
CLKIN
ModOUT
f
d
t
LH
*
t
HL
*
t
JC
t
D
Input frequency
Output frequency
Frequency Deviation
Input Frequency = 30MHz
Input Frequency = 50MHz
Parameter
Min
30
30
-
-
0.5
0.3
-
45
Typ
-
-
±1.10
± 0.65
1.1
0.8
-
50
Max
50
50
-
-
1.4
1.1
200
55
Unit
MHz
MHz
%
nS
nS
pS
%
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.
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