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Datasheet: I2779A-08TR (Alliance Semiconductor Corporation)

Low-Cost Notebook EMI Reduction IC

 

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Alliance Semiconductor Corporation
June 2005
P2779A
rev 0.1
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-Cost Notebook EMI Reduction IC

Features
Provides up to 15dB of EMI suppression
FCC approved method of EMI attenuation
Generates a 1X low EMI spread spectrum clock of
the input frequency
Operates between 20MHz and 38MHz input
frequency range
External loop filter for spread percentage adjustment
Spreading ranges from 0.25% to 2.5%
Ultra low cycle-to-cycle jitter
Zero-Cycle slip at small deviations
3.3 V Operating Voltage
10 mA output drives
TTL or CMOS compatible outputs
Low power CMOS design
Available in 8-pin SOIC and TSSOP Packages
Available for Industrial temperature operating
range (-40 C to 85 C)
Product Description
The P2779A is a versatile spread spectrum frequency
modulator designed specifically for mobile and digital
camera and other digital video and imaging applications.
The P2779A reduces electromagnetic interference (EMI) at
the clock source, which provides system-wide reduction of
EMI of all clock dependent signals. The P2779A allows
significant system cost savings by reducing the number of
circuit board layers and shielding that are traditionally
required to pass EMI regulations.
The P2779A uses the most efficient and optimized
modulation profile approved by the FCC.
The P2779A 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 P2779A is targeted toward mobile 3D graphics chip set
applications.


Block Diagram


VDD
PD
VSS
ModOUT
XIN
Frequency
Divider
Feedback
Divider
Modulation
Phase
Detector
Loop
Filter
VCO
Output
Divider
PLL
Crystal
Oscillator
XOUT
REF
LF

June 2005
P2779A
rev 0.1
Low-Cost Notebook EMI Reduction IC
2 of 8
Notice: The information in this document is subject to change without notice.
Pin Configuration










Pin Description
Pin#
Pin Name
Type
Description
1
XIN / CLKIN
I
Connect to crystal or clock input.
2 XOUT
O
Crystal
output.
3
PD
I
Power-down control pin. Pull low to enable power-down mode.
This pin has an internal pull-up resistor.
1
4 LF
I
External loop filter for the PLL. By changing the value of the CRC circuit,
the percentage spread can be adjusted accordingly.
(See Loop Filter Selection Table for detail values.)
5
VSS
P
Ground connection. Connect to system ground.
6
ModOUT
O
Spread spectrum clock output.
7
REF
O
Provides a reference clock output of the input frequency.
8
VDD
P
Connect to +3.3 V.
Note: 1. Connect to VDD if not used.

Loop Filter Selection Table VDD 3.3 V





BW = 0.50%
BW = 0.75%
BW = 1.00%
BW = 1.25%
Input
(MHz)
FS1 FS0
C1
(pF)
C2
(pF)
R1
()
C1
(pF)
C2
(pF)
R1
()
C1
(pF)
C2
(pF)
R1
()
C1
(pF)
C2
(pF)
R1
()
20
1 0 270 100,000 330 270 100,000 560 270 100,000 750
560 100,000 910
21-22 1 0 270 100,000 390 270 100,000 620 270 100,000 866(1%) 560 100,000 1,100
23-24 1 0 270 100,000 510 270 100,000 750 270 10,000 1,000
680 6,800
1,200
25-26 1 0 270 100,000 560 270 100,000 820 270 12,000 1,200
470 4,700
1,200
27-28 1 0 270 100,000 620 270 100,000 1,000 270 6,800
1,200 330
3,300 1,200
29-30 1 0 270 100,000 750 270 100,000 1,100 270 3,900
1,200 330
3,300 1,500
31-32 1 0 270 100,000 820 270 100,000 1,200 270 12,000 2,200 680
6,800 2,200
33-34 1 0 270 100,000 910 270 100,000 1,300 270 10,000 2,200 390
3,900 2,200
35-36 1 0 270 100,000 1,000 270 100,000 1,500 270 5,600
2,200 270
2,700 2,200
37-38 1 0 270 100,000 1,200 270 100,000 1,600 270 3,300
2,200 270
2,700 2,700
Please contact factory for loop filter values if desired spread settings are not listed.
C2 C1
R1
Pin 4 LF
REF
VSS
1
2
3
4
5
6
7
8
P2779A
XIN/ CLKIN
XOUT
PD
LF
VDD
ModOUT

June 2005
P2779A
rev 0.1
Low-Cost Notebook EMI Reduction IC
3 of 8
Notice: The information in this document is subject to change without notice.

Spread Spectrum Selection
The P2779A performs zero cycle slip when set at low percentage spreading. This prevents any 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 that the center frequency is the frequency of the external
reference input on XIN/CLKIN, pin 1.)
The P2779A is designed for PC peripheral, networking, notebook PC, and LCD monitor applications. It is optimized for
operation from 20MHz to 38MHz. The P2779A's spread percentage selection is determined by the external LF value
specified in the Loop Filter Selection Table. The external LF allows the user to fine tune the spread percentage to optimize
the EMI reduction benefits of the spread spectrum.
Application Schematic












PD selection: Power dissipation can be reduced by completely turning off the IC.























1
2
3
4
8
7
6
5
VDD
REF
ModOUT
VSS
LF
PD
XOUT
XIN/CLKIN
P2779A
+3.3V
Modulated 27MHz
27 MHz
C2 C1
R1
0.1F
VDD

June 2005
P2779A
rev 0.1
Low-Cost Notebook EMI Reduction IC
4 of 8
Notice: The information in this document is subject to change without notice.
Absolute Maximum Ratings
Symbol
Parameter
Rating
Unit
V
DD
, 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
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
-
60
-
A
I
IH
Input high current
-
0
-
A
I
XOL
XOUT output low current (at 0.4 V, V
DD
= 3.3V)
-
10
-
mA
I
XOH
XOUT output high current (at 2.5 V, V
DD
= 3.3V)
-
10
-
mA
V
OL
Output low voltage (V
DD
= 3.3V, I
OL
= 20 mA)
-
-
0.4
V
V
OH
Output high voltage (V
DD
= 3.3V, I
OH
= 20 mA)
2.5
-
-
V
I
DD
Static supply current
-
3
-
mA
I
CC
Dynamic supply current
(3.3 V, 25 pF loading, 32 MHz)
- 12 -
mA
V
DD
Operating
voltage 3.0
3.3
3.6
V
t
ON
Power-up time (first locked cycle after power up)
-
7
-
mS
Z
OUT
Clock output impedance
-
28
-

AC Electrical Characteristics
Symbol
Parameter
Min
Typ
Max
Unit
f
IN
Input
frequency
20 - 38 MHz
f
OUT
Output
frequency
20
-
38 MHz
t
LH
1
Output rise time (measured at 0.8 V to 2.0 V)
-
1
-
nS
t
HL
1
Output fall time (measured at 2.0 V to 0.8 V)
-
1
-
nS
t
JC
Jitter (Cycle to cycle)
-
175
-
pS
t
D
Output duty cycle
45
50
55
%
Note: 1. t
LH
and t
HL
are measured into a capacitive load of 15 pF


June 2005
P2779A
rev 0.1
Low-Cost Notebook EMI Reduction IC
5 of 8
Notice: The information in this document is subject to change without notice.
Package Information
8-lead (150-mil) SOIC Package

D
E
H
D
A1
A2
A
L
C
B
e

Dimensions
Inches
Millimeters
Symbol
Min
Max
Min
Max
A1 0.004 0.010 0.10
0.25
A 0.053
0.069 1.35 1.75
A2 0.049 0.059 1.25
1.50
B 0.012
0.020 0.31 0.51
C 0.007
0.010 0.18 0.25
D
0.193 BSC
4.90 BSC
E
0.154 BSC
3.91 BSC
e
0.050 BSC
1.27 BSC
H
0.236 BSC
6.00 BSC
L 0.016
0.050 0.41 1.27
0 8 0 8

Note: Controlling dimensions are millimeters
SOIC 0.074 grams unit weight






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