October 2003
rev 1.0
General Purpose EMI Reduction IC
Features
Provides up to 15 dB of EMI suppression
FCC approved method of EMI attenuation
Generates a 1X, 2X, and 4X low EMI spread
spectrum clock of the input frequency
Input frequency range from 3 to 78 MHz
External loop filter for spread % adjustment
Spreading ranges from ±0.25% to ±5.0%
Ultra low cycle-to-cycle jitter
Zero-cycle slip
3.3V operating voltage range
10 mA output drives
TTL or CMOS compatible outputs
Ultra-low power CMOS design
Available in 8 pin SOIC and TSSOP
Available for industrial and automotive
temperature ranges.
Product Description
The P278xx is a versatile spread spectrum
frequency modulator designed specifically for digital
camera and other digital video and imaging
applications. The P278xx reduces electromagnetic
interference (EMI) at the clock source, which
provides system wide reduction of EMI of all clock
Block Diagram
P2781/82/84
dependent signals. The P278xx allows significant
system cost savings by reducing the number of
circuit board layers and shielding that are
traditionally required to pass EMI regulations.
The P278xx uses the most efficient and
optimized modulation profile approved by the
FCC.
The P278xx 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 P278xx is targeted towards MFP, xDSL, fax
modem, set-top box, USB controller, DSC, and
embedded systems.
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.
October 2003
rev 1.0
Pin Configuration
P2781/82/84
Pin Description (P278XA)
Pin#
1
2
3
4
5
6
7
8
Pin Name
XIN/CLKIN
XOUT
FS1
LF
VSS
ModOUT
FS0
VDD
Type
I
I
I
I
I
O
I
P
Description
Connect to crystal or clock input.
Crystal output
Digital logic input used to select input frequency range (see the Input
Frequency Selection Table). This pin has an internal pull-up resistor.
External Loop Filter for the PLL. By changing the value of the CRC circuit,
the percentage spread can be adjusted accordingly. See the Loop Filter
Selection Table for detail value.
Ground Connection. Connect to system ground.
Spread Spectrum Clock Output.
Digital logic input used to select input frequency range (see the Input
Frequency Selection Table). This pin has an internal pull-up resistor.
Connect to +3.3 V
Input Frequency Selection Table
FS1
0
0
1
1
FS0
0
1
0
1
Input (MHz)
3 to 9
10 to 19
20 to 38
39 to 78
Output Frequency Scaling (MHz)
P2781X
P2782X
P2784X
3 to 9
6 to 18
12 to 36
10 to 19
20 to 38
40 to 76
20 to 38
40 to 76
80 to 152
39 to 78
78 to 156
156 to 312
Modulation Rate (KHz)
Fin / 128
Fin / 256
Fin / 512
Fin / 1024
General Purpose EMI Reduction IC
Notice: The information in this document is subject to change without notice.
2 of 9
October 2003
rev 1.0
Loop Filter Selection Table VDD 3.3V
P2781/82/84
Contact Alliance for loop values that are not listed in the table and for
component selection values for industrial and automotive temperatures.
BW = ±0.50%
Input
MHz
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21-22
23-24
25-26
27-28
29-30
31-32
33-34
35-36
37-38
39-42
43-46
47-50
51-54
55-58
59-62
63-66
67-70
71-74
75-78
FS1 FS0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
C1
(pF)
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
C2
(pF)
330,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
1
BW = ±0.75%
C1
(pF)
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
C2
(pF)
330,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
100,000
1
BW = ±1.00%
C1
(pF)
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
270
C2
(pF)
1
BW = ±1.25%
C1
(pF)
560
560
560
680
330
680
270
560
560
680
470
330
330
680
390
270
270
560
560
680
470
330
330
680
390
270
270
560
560
680
470
330
330
680
390
270
270
C2
(pF)
100,000
100,000
100,000
6,800
3,300
6,800
2,700
100,000
100,000
6,800
4,700
3,300
3,300
6,800
3,900
2,700
2,700
100,000
100,000
6,800
4,700
3,300
3,300
6,800
3,900
2,700
2,700
100,000
100,000
6,800
4,700
3,300
3,300
6,800
3,900
2,700
2,700
1
R1
(ohm)
220
270
390
510
620
820
1,000
330
390
510
560
620
750
820
910
1,000
1,200
330
390
510
560
620
750
820
910
1,000
1,200
330
390
510
560
620
750
820
910
1,000
1,200
R1
(ohm)
300
390
560
750
1,000
1,200
1,500
510
560
750
820
1,000
1,100
1,200
1,300
1,500
1,600
560
620
750
820
1,000
1,100
1,200
1,300
1,500
1,600
560
620
750
820
1,000
1,100
1,200
1,300
1,600
1,800
R1
(ohm)
R1
(ohm)
510
680
910
1,200
1,200
2,200
2,200
910
1,100
1,200
1,200
1,200
1,500
2,200
2,200
2,200
2,700
910
1,100
1,200
1,200
1,200
1,500
2,200
2,200
2,200
2,700
910
1,100
1,200
1,200
1,200
1,500
2,200
2,200
2,200
2,700
100,000
390
100,000
560
100,000
750
10,000
1,000
5,600
1,200
12,000
2,200
5,600
2,200
100,000
750
100,000 866(1%)
10,000
1,000
12,000
1,200
5,600
1,200
3,900
1,200
12,000
2,200
10,000
2,200
5,600
2,200
3,300
2,200
100,000
750
100,000 866 (1%)
10,000
1,000
12,000
1,200
6,800
1,200
3,900
1,200
12,000
2,200
10,000
2,200
5,600
2,200
3,300
2,200
100,000
750
100,000 866 (1%)
10,000
1,000
12,000
1,200
6,800
1,200
3,900
1,200
12,000
2,200
8,200
2,200
5,600
2,200
3,300
2,200
1 The BW value is representative of typical conditions
General Purpose EMI Reduction IC
Notice: The information in this document is subject to change without notice.
3 of 9
October 2003
rev 1.0
P2781/82/84
Spread Spectrum Selection
The P278xA performs Zero Cycle Slip when set at low percentage spreading. This allows no
occurrence of system timing error. The optimal setting should minimize system EMI to the fullest
without affecting system performance. The spreading is described as a percentage deviation of the
center frequency. (Note: the center frequency is the frequency of the external reference input on
CLKIN, Pin 1.)
The P2781A is designed for PC peripheral, networking, notebook PC, and LCD monitor applications. It
is optimized for operation between 3 to 78 MHz range. In the following application schematic example,
the P2781A spread percentage selection is determined by the external LF value specified in the Loop
Filter Selection Table. The Input Frequency Selection Table specifies the input frequency range. The
external LF allows the user to fine tune the spread percentage to optimize the EMI reduction benefits
of the spread spectrum.
Note: Both logic input pins FS1 and FS0 have to be connected to either VDD or VSS. Do not leave
them floating.
General Purpose EMI Reduction IC
Notice: The information in this document is subject to change without notice.
4 of 9
October 2003
rev 1.0
Absolute Maximum Ratings
Symbol
V
DD
, V
IN
T
STG
T
A
Parameter
Voltage on any pin with respect to GND
Storage temperature
Operating temperature
Rating
-0.5 to + 7.0
-65 to +125
0 to +70
P2781/82/84
Unit
V
°C
°C
DC Electrical Characteristics
Symbol
V
IL
Input low voltage
V
IH
I
IL
I
IH
I
XOL
I
XOH
V
OL
V
OH
I
DD
I
CC
V
DD
Input high voltage
Input low current (internal input pull-up resistor on FS0
and FS1)
Input high current (internal input pull-up resistor on
FS0 and FS1)
XOUT output low current
XOUT output high current
Output low voltage (V
DD
= 3.3 V, I
OL
= 20 mA)
Output high voltage (V
DD
= 3.3 V, I
OH
= 20 mA)
Static supply current
Typical dynamic supply current (25 pF scope probe
loading)
Operating voltage
Parameter
Min
GND – 0.3
2.0
–
–
–
–
–
2.5
-
5.2 at 3 MHz
3.0
Typ
–
–
60
0
10
10
–
–
3
–
3.3
Max
0.8
V
DD
+0.3
–
–
–
–
0.4
Unit
V
V
µA
µA
mA
mA
V
V
mA
mA
V
-
-
21.2 at 82 MHz
3.6
AC Electrical Characteristics
Symbol
f
IN
f
OUT
t
LH
Parameter
Input frequency: P278XX
Output frequency:
P2781X
P2782X
P2784X
Min
3
3
6
12
1
1
±250
±1 at 3 MHz
-20
0
±2 at 82 MHz
+20
Typ
Max
78
78
156
312
Unit
MHz
MHz
ns
ns
ps
%
%
P278XX
P278XX
P2781X
P2781X
t
HL
t
JC
t
D
∆F
P278XX
Output rise time (measured at 0.8 V to 2.0 V,
25 pF scope probe loading)
Output fall time (measured at 2.0 V to 0.8 V,
25 pF scope probe loading)
Jitter (cycle to cycle, ± 6sigma, 1000 sweeps,
± 0.5% spread, I/O frequency = 16 MHz)
Output duty cycle deviation (error from 50%
duty cycle, 25 pF scope probe loading)
Frequency deviation tolerance from BW%
stated in the Loop Filter Selection Table
General Purpose EMI Reduction IC
Notice: The information in this document is subject to change without notice.
5 of 9
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