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參數(shù)資料
| 型號： | NBC12429A |
| 廠商： | ON SEMICONDUCTOR |
| 英文描述： | 3.3V/5V Programmable PLL Synthesized Clock Generator(3.3V/5V可編程PLL合成時鐘發(fā)生器) |
| 中文描述： | 3.3V/5V的可編程鎖相環(huán)路合成時鐘發(fā)生器（3.3V/5V的可編程PLL頻率合成時鐘發(fā)生器） |
| 文件頁數(shù)： | 12/20頁 |
| 文件大?。?/td> | 351K |
| 代理商： | NBC12429A |
NBC12429, NBC12429A
http://onsemi.com
12
APPLICATIONS INFORMATION
Using the On--Board Crystal Oscillator
The NBC12429 and NBC12429A feature a fully
integrated on--board crystal oscillator to minimize system
implementation costs. The oscillator is a series resonant,
multivibrator type design as opposed to the more common
parallel resonant oscillator design. The series resonant
design provides better stability and eliminates the need for
large on chip capacitors. The oscillator is totally self
containedsothattheonlyexternalcomponentrequiredisthe
crystal.Astheoscillatorissomewhatsensitivetoloadingon
itsinputs,theuserisadvisedtomountthecrystalascloseto
thedeviceaspossibletoavoidanyboardlevelparasitics.To
facilitate
co--location,
surface
recommended,butnotrequired.Becausetheseriesresonant
design is affected by capacitive loading on the crystal
terminals, loading variation introduced by crystals from
differentvendorscouldbeapotentialissue.Forcrystalswith
a higher shunt capacitance, it may be required to place a
resistance across the terminals to suppress the third
harmonic. Although typically not required, it is a good idea
to layoutthePCBwith theprovision ofadding thisexternal
resistor. The resistor value will typically be between 500
Ω
and 1 k
Ω
.
The oscillator circuit is a series resonant circuit and thus,
for optimum performance, a series resonant crystal should
be used. Unfortunately, most crystals are characterized in a
parallel resonant mode. Fortunately, there is no physical
difference between a seriesresonant and a parallelresonant
crystal. The difference is purely in the way the devices are
characterized. As a result, a parallel resonant crystal can be
used with the device with only a minor error in the desired
frequency. A parallel resonant mode crystal used in a series
resonantcircuitwillexhibitafrequencyofoscillationafew
hundred ppm lower than specified (a few hundred ppm
translates to kHz inaccuracies). In a general computer
application, this level of inaccuracy is immaterial. Table 12
below specifies the performance requirements of the
crystals to be used with the device.
mount
crystals
are
Table 12. Crystal Specifications
Parameter
Value
Crystal Cut
Fundamental AT Cut
Resonance
Series Resonance*
Frequency Tolerance
±
75 ppm at 25
°
C
Frequency/Temperature Stability
±
150 ppm 0 to 70
°
C
Operating Range
0 to 70
°
C
Shunt Capacitance
5--7 pF
Equivalent Series Resistance (ESR)
50 to 80
Ω
Correlation Drive Level
100
m
W
Aging
5 ppm/Yr (First 3 Years)
*See accompanying text for series versus parallel resonant
discussion.
Power Supply Filtering
The
NBC12429
analog/digital products and as such, exhibit some
sensitivities that would not necessarily be seen on a fully
digital product. Analog circuitry is naturally susceptible to
random noise, especially if this noise is seen on the power
supply pins. The NBC12429 and NBC12429A provide
separate power supplies for the digital circuitry (V
CC
) and
the internal PLL (PLL_V
CC
) of the device. The purpose of
thisdesigntechniqueistotryandisolatethehighswitching
noise of the digital outputs from the relatively sensitive
internalanalogPLL.Inacontrolledenvironmentsuchasan
evaluation board, this level of isolation is sufficient.
However, in a digital system environment where it is more
difficult to minimize noise on the power supplies, a second
level of isolation may be required. The simplest form of
isolationisapowersupplyfilteronthePLL_V
CC
pinforthe
NBC12429 and NBC12429A.
Figure 8 illustrates a typical power supply filter scheme.
The NBC12429 and NBC12429A are most susceptible to
noise with spectral content in the 1 kHz to 1 MHz range.
Therefore, the filter should be designed to target this range.
The key parameter that needs to be met in the final filter
design is the DC voltage drop that will be seen between the
V
CC
supply and the PLL_V
CC
pin of the NBC12429 and
NBC12429A. From the data sheet, the PLL_V
CC
current
(the current sourced through the PLL_V
CC
pin) is typically
23 mA (27 mA maximum). Assuming that a minimum of
2.8 V must be maintained on the PLL_V
CC
pin, very little
DC voltage drop can be tolerated when a 3.3 V V
CC
supply
is used. The resistor shown in Figure 8 must have a
resistanceof10 -- 15
Ω
tomeetthevoltagedropcriteria.The
RC filter pictured will provide a broadband filter with
approximately 100:1 attenuation for noise whose spectral
contentisabove20 kHz.Asthenoisefrequencycrossesthe
series resonant point of an individual capacitor, it’s overall
impedancebeginsto look inductiveand thusincreaseswith
increasing frequency. The parallel capacitor combination
shown ensures that a low impedance path to ground exists
for frequencies well above the bandwidth of the PLL.
and
NBC12429A
are
mixed
Figure 8. Power Supply Filter
PLL_V
CC
V
CC
NBC12429
NBC12429A
0.01
m
F
22
m
F
L=1000
m
H
R=15
Ω
0.01
m
F
3.3 V or
5.0 V
R
S
= 10--15
Ω
3.3 V or
5.0 V
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| NBC12429AFA | 功能描述:鎖相環(huán) - PLL 3.3V/5V Programmable RoHS:否 制造商:Silicon Labs 類型:PLL Clock Multiplier 電路數(shù)量:1 最大輸入頻率:710 MHz 最小輸入頻率:0.002 MHz 輸出頻率范圍:0.002 MHz to 808 MHz 電源電壓-最大:3.63 V 電源電壓-最小:1.71 V 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 封裝 / 箱體:QFN-36 封裝:Tray |
| NBC12429AFAG | 功能描述:鎖相環(huán) - PLL 3.3V/5V Programmable PLL Clock Generator RoHS:否 制造商:Silicon Labs 類型:PLL Clock Multiplier 電路數(shù)量:1 最大輸入頻率:710 MHz 最小輸入頻率:0.002 MHz 輸出頻率范圍:0.002 MHz to 808 MHz 電源電壓-最大:3.63 V 電源電壓-最小:1.71 V 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 封裝 / 箱體:QFN-36 封裝:Tray |
| NBC12429AFAR2 | 功能描述:時鐘發(fā)生器及支持產(chǎn)品 3.3V/5V Programmable RoHS:否 制造商:Silicon Labs 類型:Clock Generators 最大輸入頻率:14.318 MHz 最大輸出頻率:166 MHz 輸出端數(shù)量:16 占空比 - 最大:55 % 工作電源電壓:3.3 V 工作電源電流:1 mA 最大工作溫度:+ 85 C 安裝風格:SMD/SMT 封裝 / 箱體:QFN-56 |
| NBC12429AFAR2G | 功能描述:鎖相環(huán) - PLL 3.3V/5V Programmable PLL Clock Generator RoHS:否 制造商:Silicon Labs 類型:PLL Clock Multiplier 電路數(shù)量:1 最大輸入頻率:710 MHz 最小輸入頻率:0.002 MHz 輸出頻率范圍:0.002 MHz to 808 MHz 電源電壓-最大:3.63 V 電源電壓-最小:1.71 V 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 封裝 / 箱體:QFN-36 封裝:Tray |
| NBC12429AFN | 功能描述:鎖相環(huán) - PLL 3.3V/5V Programmable RoHS:否 制造商:Silicon Labs 類型:PLL Clock Multiplier 電路數(shù)量:1 最大輸入頻率:710 MHz 最小輸入頻率:0.002 MHz 輸出頻率范圍:0.002 MHz to 808 MHz 電源電壓-最大:3.63 V 電源電壓-最小:1.71 V 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 封裝 / 箱體:QFN-36 封裝:Tray |
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