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| 型号： | LMK04031BEVAL/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 43/65页 |
| 文件大小： | 0K |
| 描述： | EVAL BOARD LMK04031BISQ |
| 标准包装： | 1 |
| 系列： | PowerWise® |
| 主要目的： | 计时，多用途 |
| 嵌入式： | 否 |
| 已用 IC / 零件： | LMK04031 |
| 已供物品： | 板，线缆，文档，软件 |
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2
CL = 6 + 6 +
4
= 14 pF
2
CSTRAY
CL = CTUNE + CIN +
C
Po
u
t1
LMK040xx
OSCin
OSCin*
Copt
PLL1 Loop Filter
XTAL
CC1 = 2.2 nF
CC2 = 2.2 nF
R1 = 4.7k
R3 = 10k
Copt
1 nF
R2 = 4.7k
SMV1249-074LF
SNOSAZ8J – SEPTEMBER 2008 – REVISED SEPTEMBER 2011
Figure 16. Reference Design Circuit for Crystal Oscillator Option
Optional Crystal Oscillator Implementation (OSCin/OSCin*)
The LMK04000 family features supporting circuitry for a discretely implemented oscillator driving the OSCin port
pins. Figure 16 illustrates a reference design circuit for a crystal oscillator:
This circuit topology represents a parallel resonant mode oscillator design. When selecting a crystal for parallel
resonance, the total load capacitance, CL, must be specified. The load capacitance is the sum of the tuning
capacitance (CTUNE), the capacitance seen looking into the OSCin port (CIN), and stray capacitance due to PCB
parasitics (CSTRAY), and is given by:
CTUNE is provided by the varactor diode shown in Figure 16, Skyworks model SMV1249-074. A dual diode
package with common cathode and provides the variable capacitance for tuning. The single diode capacitance
ranges from approximately 31 pF at 0.3 V to 3.4 pF at 3 V. The capacitance range of the dual package (anode to
anode) is approximately 15.5 pF at 3 V to 1.7 pF at 0.3 V. The desired value of VTUNE applied to the diode should
be VCC/2, or 1.65 V for VCC = 3.3 V. The typical performance curve from the data sheet for the SMV1249-074
indicates that the capacitance at this voltage is approximately 6 pF (12 pF/2).
The nominal input capacitance (CIN) of the LMK04000 family OSCin pins is 6 pF. The stray capacitance (CSTRAY)
of the PCB should be minimized by arranging the oscillator circuit layout to achieve trace lengths as short as
possible and as narrow as possible trace width (50
Ω characteristic impedance is not required). As an example,
assume that CSTRAY is 4 pF. The total load capacitance is nominally:
Consequently the load capacitance specification for the crystal in this case should be nominally 14 pF.
48
Copyright 2008–2011, Texas Instruments Incorporated
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LMK04031BEVALXO | 功能描述:时钟和定时器开发工具 LMK04031 EVAL BOARD RoHS:否 制造商:Texas Instruments 产品:Evaluation Modules 类型:Clock Conditioners 工具用于评估:LMK04100B 频率:122.8 MHz 工作电源电压:3.3 V |
| LMK04031BISQ | 制造商:Texas Instruments 功能描述:Clock Conditioner 48-Pin LLP EP T/R |
| LMK04031BISQ/NOPB | 功能描述:时钟合成器/抖动清除器 RoHS:否 制造商:Skyworks Solutions, Inc. 输出端数量: 输出电平: 最大输出频率: 输入电平: 最大输入频率:6.1 GHz 电源电压-最大:3.3 V 电源电压-最小:2.7 V 封装 / 箱体:TSSOP-28 封装:Reel |
| LMK04031BISQE | 制造商:Texas Instruments 功能描述:PRECISION CLOCK CONDITIONER, 48LLP |
| LMK04031BISQE/NOPB | 功能描述:时钟合成器/抖动清除器 RoHS:否 制造商:Skyworks Solutions, Inc. 输出端数量: 输出电平: 最大输出频率: 输入电平: 最大输入频率:6.1 GHz 电源电压-最大:3.3 V 电源电压-最小:2.7 V 封装 / 箱体:TSSOP-28 封装:Reel |
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