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November 2003  
rev 1.0  
ASM3P2531A  
Features  
dependent signals. It allows significant system cost  
ꢀ
ꢀ
FCC approved method of EMI attenuation.  
savings by reducing the number of circuit board layers  
and shielding traditionally required to pass EMI  
regulations.  
Generates a low EMI spread spectrum of the  
input clock frequency.  
ꢀ
ꢀ
Optimized for input frequency range between  
35MHz – 55MHz.  
The ASM3P2531A modulates the output of a single 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.  
Internal loop filter minimizes external  
components and board space.  
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Frequency Deviation: ±1.65%.  
Low inherent cycle-to-cycle jitter.  
3.3 V or 5 V operating voltage.  
CMOS/TTL compatible inputs and outputs.  
Ultra low power CMOS design: 5.50 mA @3.3 V.  
Supports notebook VGA and other LCD timing  
controller applications.  
The ASM3P2531A uses the most efficient and optimized  
modulation profile approved by the FCC and is  
ꢀ
Available in 8-pin SOIC and TSSOP.  
implemented by using a proprietary all-digital method.  
Product Description  
The ASM3P2531A is a versatile spread spectrum  
frequency modulator designed specifically for a wide  
range of clock frequencies. It reduces electromagnetic  
interference (EMI) at the clock source allowing system-  
wide reduction of EMI of downstream clock and data  
Applications  
The ASM3P2531A is targeted toward the notebook VGA  
chip and other displays using an LVDS interface, PC  
peripheral devices, and embedded systems  
Block Diagram  
STOP  
VDD  
PLL  
Modulation  
CLKIN  
Crystal  
Oscillator  
Frequency  
Divider  
Output  
Divider  
Phase  
Detector  
Loop  
Filter  
VCO  
Feedback  
Divider  
MODOUT  
VSS  
Low Frequency EMI Reduction  
1 of 8  
Notice: The information in this document is subject to change without notice.  
November 2003  
rev 1.0  
ASM3P2531A  
Pin Configuration  
8
7
NC  
NC  
CLKIN  
VDD  
1
2
NC  
6
5
3
4
VSS  
STOP  
ModOUT  
ASM3P2531A  
Spread Range Selection, VDD = 3.3 V  
CLKIN frequency  
Spreading range  
Modulation rate  
(CLKIN/1280) KHz  
35 MHz – 55 MHz  
±1.65%  
Pin Description  
Pin# Pin Name Type  
Description  
1
2
3
4
CLKIN  
VDD  
I
External reference frequency input.  
Power supply for the entire chip.  
Ground to entire chip.  
P
P
O
VSS  
ModOUT  
Spread spectrum clock output or reference output. Refer Standby Mode Selection.  
5
STOP  
I
Active LOW signal. When HIGH, enables ModOUT and when LOW, ModOUT  
would be LOW.  
6
7
8
NC  
NC  
NC  
-
-
-
No connect.  
No connect.  
No connect.  
Low Frequency EMI Reduction  
2 of 8  
Notice: The information in this document is subject to change without notice.  
November 2003  
rev 1.0  
ASM3P2531A  
Schematic for a Typical Application  
ASM3P3531A  
Input clock 35MHz – 55MHz  
VDD  
CLKIN  
NC  
1
2
8
7
6
5
0.1µF  
Ferrite  
Bead  
VDD  
VSS  
NC  
NC  
3
4
VDD  
0Ω  
STOP  
ModOUT  
0Ω  
EMI reduced clock output  
35MHz – 55MHz  
Use either pull-up or pull-  
down resistors with 0Ω  
Low Frequency EMI Reduction  
3 of 8  
Notice: The information in this document is subject to change without notice.  
November 2003  
rev 1.0  
ASM3P2531A  
Absolute Maximum Ratings  
Symbol  
Parameter  
Rating  
-0.5 to +7.0  
-65 to +125  
0 to +70  
Unit  
V
VDD, VIN  
TSTG  
Voltage on any pin with respect to GND  
Storage temperature  
° C  
° C  
TA  
Operating temperature  
DC Electrical Characteristics  
Symbol  
Parameter  
Min  
GND - 0.3  
2.0  
Typ  
Max  
Unit  
V
VIL  
VIH  
IIL  
Input low voltage  
Input high voltage  
Input low current  
Input high current  
0.8  
VDD + 0.3  
-35  
V
µA  
µA  
V
IIH  
35  
VDD = 3.3 V, IOL = 20 mA  
DD = 5.0 V, IOL = 20 mA  
VDD = 3.3 V, IOL = 20 mA  
DD = 5.0 V, IOL = 20 mA  
0.4  
VOL  
Output low voltage  
Output high voltage  
V
V
2.5  
4.5  
V
VOH  
IDD  
V
V
Static supply current standby mode  
Normal mode  
0.6  
mA  
fIN-min  
3.2  
fIN-typ  
fIN-max  
7.0  
ICC  
Dynamic supply current  
3.3 V and 10 pF loading  
5.0 V and 10 pF loading  
mA  
mA  
V
6.2  
13.6  
5.5  
VDD  
tON  
Operating voltage  
2.7  
3.3  
0.18  
50  
Power-up time (first locked cycle after power up)  
Clock output impedance  
mS  
Ω
ZOUT  
AC Electrical Characteristics  
Symbol  
Parameter  
Min  
35  
Typ  
Max  
55  
Unit  
MHz  
MHz  
ns  
fIN  
Input frequency  
fOUT  
Output frequency  
35  
55  
Measured at 0.8 V to 2.0 V  
Measured at 1.2 V to 3.75 V  
Measured at 2.0 V to 0.8 V  
Measured at 1.2 V to 3.75 V  
0.7  
0.9  
0.75  
0.8  
1.1  
1
tLH  
Output rise time  
Output fall time  
ns  
0.6  
45  
1.0  
ns  
1
tHL  
0.75  
ns  
tJC  
TD  
Jitter (cycle to cycle)  
Output duty cycle  
360  
55  
ps  
50  
%
Low Frequency EMI Reduction  
4 of 8  
Notice: The information in this document is subject to change without notice.  
November 2003  
rev 1.0  
ASM3P2531A  
Package Information  
8-Pin SOIC  
Symbol  
Dimensions in inches  
Dimensions in millimeters  
Min  
Max  
Min  
1.35  
0.10  
0.33  
0.18  
4.78  
3.80  
5.80  
Max  
1.75  
0.25  
0.53  
0.27  
5.00  
4.01  
6.20  
A
A1  
B
C
D
E
H
e
0.053  
0.004  
0.013  
0.007  
0.188  
0.150  
0.228  
0.069  
0.010  
0.022  
0.012  
0.197  
0.158  
0.244  
0.050 BSC  
1.27 BSC  
L
0.016  
0°  
0.035  
8°  
0.40  
0°  
0.89  
8°  
θ
Low Frequency EMI Reduction  
5 of 8  
Notice: The information in this document is subject to change without notice.  
November 2003  
rev 1.0  
ASM3P2531A  
Package Information  
8-Pin TSSOP  
Symbol  
Dimensions in inches  
Dimensions in millimeters  
Min  
-
Max  
Min  
-
Max  
1.10  
0.15  
0.95  
0.30  
0.20  
3.10  
A
A1  
A2  
B
0.043  
0.006  
0.037  
0.012  
0.008  
0.122  
0.002  
0.033  
0.008  
0.004  
0.114  
0.05  
0.85  
0.19  
0.09  
2.90  
C
D
H
E
0.252 BSC  
6.40 BSC  
0.65 BSC  
0.169  
0.177  
4.30  
4.50  
e
0.026 BSC  
L
0.020  
0°  
0.028  
8°  
0.50  
0°  
0.70  
8°  
θ
Low Frequency EMI Reduction  
6 of 8  
Notice: The information in this document is subject to change without notice.  
November 2003  
rev 1.0  
ASM3P2531A  
Ordering Information  
Ordering Code  
ASM3P2531A-08ST  
ASM3P2531A-08SR  
ASM3I2531A-08ST  
ASM3I2531A-08SR  
ASM3P2531A-08TT  
ASM3P2531A-08TR  
ASM3I2531A-08TT  
ASM3I2531A-08TR  
Package Type  
Operating Range  
Commercial  
Commercial  
Industrial  
8-pin 150mil SOIC -TUBE  
8-pin 150-mil SOIC -TAPE & REEL  
8-pin 150mil SOIC -TUBE  
8-pin 150-mil SOIC -TAPE & REEL  
8-pin 4.4mm TSSOP -TUBE  
8-pin 4.4mm TSSOP -TAPE & REEL  
8-pin 4.4mm TSSOP -TUBE  
8-pin 4.4mm TSSOP - TAPE & REEL  
Industrial  
Commercial  
Commercial  
Industrial  
Industrial  
Ordering Information  
OR - SOT23/T/R  
SR - SOIC, T/R  
TT – TSSOP, TUBE  
TR - TSSOP, T/R  
VT – TVSOP, TUBE  
VR – TVSOP, T/R  
ST – SOIC, TUBE  
QR – QFN, T/R  
QT - QFN, TUBE  
BT - BGA, TUBE  
BR – BGA, T/R  
A S M 3 P 2 5 3 1 A - 0 8 T R  
PIN COUNT  
PART NUMBER  
X = Automotive  
I = Industrial  
P or n/c = Commercial  
1 – reserved  
2 - Non PLL based  
3 – EMI Reduction  
4 – DDR support products  
5 – STD Zero Delay Buffer  
6 – power management  
7 – power management  
8 – power management  
9 – Hi performance  
0 - reserved  
Alliance Semiconductor Mixed Signal Product  
Low Frequency EMI Reduction  
7 of 8  
Notice: The information in this document is subject to change without notice.  
November 2003  
rev 1.0  
ASM3P2531A  
Alliance Semiconductor Corporation  
2595, Augustine Drive,  
Santa Clara, CA 95054  
Tel# 408-855-4900  
Copyright © Alliance Semiconductor  
All Rights Reserved  
Preliminary Information  
Part Number: ASM3P2531A  
Document Version: v1.0  
Fax: 408-855-4999  
www.alsc.com  
© Copyright 2003 Alliance Semiconductor Corporation. All rights reserved. Our three-point logo, our name and Intelliwatt are  
trademarks or registered trademarks of Alliance. All other brand and product names may be the trademarks of their  
respective companies. Alliance reserves the right to make changes to this document and its products at any time without  
notice. Alliance assumes no responsibility for any errors that may appear in this document. The data contained herein  
represents Alliance's best data and/or estimates at the time of issuance. Alliance reserves the right to change or correct this  
data at any time, without notice. If the product described herein is under development, significant changes to these  
specifications are possible. The information in this product data sheet is intended to be general descriptive information for  
potential customers and users, and is not intended to operate as, or provide, any guarantee or warrantee to any user or  
customer. Alliance does not assume any responsibility or liability arising out of the application or use of any product  
described herein, and disclaims any express or implied warranties related to the sale and/or use of Alliance products  
including liability or warranties related to fitness for a particular purpose, merchantability, or infringement of any intellectual  
property rights, except as express agreed to in Alliance's Terms and Conditions of Sale (which are available from Alliance).  
All sales of Alliance products are made exclusively according to Alliance's Terms and Conditions of Sale. The purchase of  
products from Alliance does not convey a license under any patent rights, copyrights; mask works rights, trademarks, or any  
other intellectual property rights of Alliance or third parties. Alliance does not authorize its products for use as critical  
components in life-supporting systems where a malfunction or failure may reasonably be expected to result in significant  
injury to the user, and the inclusion of Alliance products in such life-supporting systems implies that the manufacturer  
assumes all risk of such use and agrees to indemnify Alliance against all claims arising from such use.  
Low Frequency EMI Reduction  
8 of 8  
Notice: The information in this document is subject to change without notice.