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I2779A - ETC - Low-Cost Notebook EMI Reduction IC

Номер произв I2779A
Описание Low-Cost Notebook EMI Reduction IC
Производители ETC
логотип ETC логотип 
предварительный просмотр
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I2779A Даташит, Описание, Даташиты
Production
February 2003
® P2779A
Low-Cost Notebook EMI Reduction IC
Features
• Provides up to 15 dB 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 fre-
quency range
• External loop filter for spread percentage adjust-
ment
• 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 range
• 10 mA output drives
• TTL or CMOS compatible outputs
• Low power CMOS design
• Available in 8-pin SOIC and TSSOP
• Available for industrial temperature operating
range (-40º C to 85º C)
Block Diagram
PD LF VDD
XIN
XOUT
Crystal
oscillator
REF
Frequency
divider
Feedback
divider
Modulation
Phase
detector
Loop
filter
PLL
VCO
Output
divider
ModOUT
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
VSS
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
Pin Diagram
XIN/CLKIN 1
XOUT 2
PD 3
LF 4
8 VDD
7 REF
6 ModOUT
5 VSS
Alliance Semiconductor
2575 Augustine Drive • Santa Clara, CA 95054 • Tel: 408.855.4900 • Fax: 408.855.4999 • www.alsc.com
Notice: The information in this document is subject to change without notice.
--------------------------------------------

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I2779A Даташит, Описание, Даташиты
P2779A
®
Pin Description
Pin #
1
2
3
Name
XIN/CLKIN
XOUT
PD
Type
I
I
I
4 LF I
5 VSS P
6 ModOUT O
7 REF O
8 VDD P
1. Connect to VDD if not used.
Description
Connect to crystal or clock input.
Crystal output.
Power-down control pin. Pull low to enable power-down mode. This pin has an
internal pull-up resistor.1
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 value.)
Ground connection. Connect to system ground.
Spread Spectrum clock output.
Provides a reference clock output of the input frequency.
Connect to +3.3 V.
Loop Filter Selection Table VDD 3.3 V
R1
Pin 4 LF
C2 C1
BW = ± 0.50%
BW = ± 0.75%
BW = ± 1.00%
BW = ± 1.25%
Input
(MHz)
FS1
FS0
C1
C2
R1 C1 C2
R1 C1 C2
R1 C1 C2
R1
(pF) (pF) (ohms) (pF) (pF) (ohms) (pF) (pF) (ohms) (pF) (pF) (ohms)
20
21 - 22
23 - 24
25 - 26
27 - 28
29 - 30
31 - 32
33 - 34
35 - 36
37 - 38
1
1
1
1
1
1
1
1
1
1
0 270 100,000 330 270 100,000 560 270 100,000 750 560 100,000 910
0 270 100,000 390 270 100,000 620 270 100,000 866(1%) 560 100,000 1,100
0 270 100,000 510 270 100,000 750 270 10,000 1,000 680 6,800 1,200
0 270 100,000 560 270 100,000 820 270 12,000 1,200 470 4,700 1,200
0 270 100,000 620 270 100,000 1,000 270 6,800 1,200 330 3,300 1,200
0 270 100,000 750 270 100,000 1,100 270 3,900 1,200 330 3,300 1,500
0 270 100,000 820 270 100,000 1,200 270 12,000 2,200 680 6,800 2,200
0 270 100,000 910 270 100,000 1,300 270 10,000 2,200 390 3,900 2,200
0 270 100,000 1,000 270 100,000 1,500 270 5,600 2,200 270 2,700 2,200
0 270 100,000 1,200 270 100,000 1,600 270 3,300 2,200 270 2,700 2,700
Plese contact factory for loop filter values if desired spread settings are not listed.
February 2003
Low-Cost Notebook EMI Reduction IC
Notice: The information in this document is subject to change without notice.
2 of 6
--------------------------------------------

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I2779A Даташит, Описание, Даташиты
P2779A
®
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 CLKIN, pin 1.)
The P2779A is designed for PC peripheral, networking, notebook PC, and LCD monitor applications. It is optimized
for operation from 20 MHz to 38 MHz. 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
27 MHz
C2
1 CLKIN
VDD 8
2 XOUT
VDD
3 PD
REF 7
ModOUT 6
R1
C1
4 LF
P2779A
VSS 5
0.1 uF
+3.3 V
Modulated 27 MHz
PD selection: Power dissipation can be reduced by completely turning off the IC.
February 2003
Low-Cost Notebook EMI Reduction IC
Notice: The information in this document is subject to change without notice.
3 of 6
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