shielding that are required to pass EMI regulations. The
ASM3P2853A modulates the output of 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
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.
Modulation rate: 39 KHz.
Spread Spectrum ON/OFF control
Supply voltage range 2.5V ± 5%.
Available in 8-pin SOIC package.
Commercial Temperature range.
Applications
ASM3P2853A is targeted towards EMI management for
high speed digital applications such as PC peripheral
devices, consumer electronics and embedded controller
systems.
Product Description
The ASM3P2853A is a versatile spread spectrum
frequency
modulator.
The
ASM3P2853A
reduces
electromagnetic interference (EMI) at the clock source.
The ASM3P2853A allows significant system cost savings
by reducing the number of circuit board layers and
Block Diagram
V
DD
PWDNB
XIN
XOUT
Crystal
Oscillator
PLL1
USB Clock
(48 MHz
Unmodulated)
50 MHz
Modulated
SSONB
PLL2
V
SS
Alliance Semiconductor
2575 Augustine Drive
•
Santa Clara CA
•
Tel: 408-855-4900
•
Fax: 408-855-4999
•
www.alsc.com
December 2004
rev 0.7
Pin Configuration
ASM3P2853A
XIN
XOUT
V
DD
V
SS
1
2
3
4
8
50 MHz
USB Clock
SSONB
PWDNB
7
ASM3P2853A
6
5
Pin Description
Pin Name
XIN
Type
I
Description
Connection to crystal or external reference frequency input. This pin has dual
functions. It can be connected either to an external crystal or an external
reference clock.
Connection to crystal. If using an external reference clock, this pin must be left
unconnected.
Power supply for the analog and digital blocks
Ground to entire chip.
Power-down control pin. Pull low to enable the power-down mode. Connect to
VDD, if not used.
Digital logic input used to enable spread spectrum function (Active LOW).
Spread spectrum is enabled when LOW, disabled when HIGH.
Clock output -1 (48 MHz unmodulated)
Clock output -2 (50 MHz modulated)
XOUT
V
DD
V
SS
PWDNB
SSONB
USB Clock
50 MHz
O
P
P
I
I
O
O
Peak EMI Reducing Solution
2 of 8
December 2004
rev 0.7
Absolute Maximum Ratings
Symbol
V
DD
V
I
V
O
I
IK
I
OK
T
J
Input voltage, DC
Output voltage, DC
Input clamp current (V
I
<0 or V
I
>V
DD
)
Output clamp current (V
I
<0 or V
I
>V
DD
)
Junction temperature
Lead temperature (soldering 10 sec)
Input static discharge voltage protection
(MIL –STD 883E, Method 3015.7)
reliability.
ASM3P2853A
Parameter
Supply voltage, DC
Rating
(V
SS
– 0.5) to 7
(V
SS
-0.5) to (V
DD
+0.5)
(V
SS
-0.5) to (V
DD
+ 0.5)
-50 to +50
-50 to +50
150
260
2
Unit
V
V
V
mA
mA
°C
°C
kV
Note: These are stress ratings only and functional operation is not implied. Exposure to absolute maximum ratings for extended periods may affect device
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