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LNK302DG 参数 Datasheet PDF下载

LNK302DG图片预览
型号: LNK302DG
PDF下载: 下载PDF文件 查看货源
内容描述: 使用LinkSwitch -TN系列元件数最少,节能艾菲cient离线式开关IC [LinkSwitch-TN Family Lowest Component Count, Energy-Effi cient Off-Line Switcher IC]
分类和应用: 开关
文件页数/大小: 20 页 / 712 K
品牌: POWERINT [ Power Integrations ]
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LNK302/304-306  
KEY FEATURES  
TOPOLOGY  
BASIC CIRCUIT SCHEMATIC  
Low-Side  
1. Output referenced to input  
2. Positive output (VO) with respect to +VIN  
3. Step up/down – VO > VIN or VO < VIN  
4. Optocoupler feedback  
Buck Boost –  
Optocoupler  
Feedback  
+
LinkSwitch-TN  
- Accuracy only limited by reference  
choice  
VIN  
VO  
- Low cost non-safety rated opto  
- No pre-load required  
5. Fail-safe – output is not subjected to input  
voltage if the internal MOSFET fails  
BP  
FB  
+
D
S
PI-3756-111903  
Table 2 (cont). Common Circuit Congurations Using LinkSwitch-TN.  
provides the lowest cost and highest efciency converter. CCM  
designs require a larger inductor and ultra-fast (trr 35 ns)  
freewheeling diode in all cases. It is lower cost to use a larger  
LinkSwitch-TNinMDCMthanasmallerLinkSwitch-TNinCCM  
because of the additional external component costs of a CCM  
design. However, ifthehighestoutputcurrentisrequired, CCM  
should be employed following the guidelines below.  
Feedback Diode D2  
Diode D2 can be a low-cost slow diode such as the 1N400X  
series, however it should be specied as a glass passivated type  
to guarantee a specied reverse recovery time. To a rst order,  
the forward drops of D1 and D2 should match.  
Inductor L1  
Choose any standard off-the-shelf inductor that meets the  
design requirements. A “drum” or “dog bone” “I” core  
inductor is recommended with a single ferrite element due to  
its low cost and very low audible noise properties. The typical  
inductance value and RMS current rating can be obtained from  
the LinkSwitch-TN design spreadsheet available within the  
PI Expert design suite from Power Integrations. Choose L1  
greater than or equal to the typical calculated inductance with  
RMS current rating greater than or equal to calculated RMS  
inductor current.  
Topology Options  
LinkSwitch-TN can be used in all common topologies, with or  
withoutanoptocouplerandreferencetoimproveoutputvoltage  
tolerance and regulation. Table 2 provide a summary of these  
congurations. For more information see the Application  
Note – LinkSwitch-TN Design Guide.  
Component Selection  
Referring to Figure 5, the following considerations may be  
Capacitor C2  
helpful in selecting components for a LinkSwitch-TN design.  
The primary function of capacitor C2 is to smooth the inductor  
current. The actual output ripple voltage is a function of this  
capacitor’s ESR. To a rst order, the ESR of this capacitor  
shouldnotexceedtheratedripplevoltagedividedbythetypical  
current limit of the chosen LinkSwitch-TN.  
Freewheeling Diode D1  
Diode D1 should be an ultra-fast type. For MDCM, reverse  
recovery time trr 75 ns should be used at a temperature of  
70°Corbelow. Slowerdiodesarenotacceptable,ascontinuous  
mode operation will always occur during startup, causing high  
leading edge current spikes, terminating the switching cycle  
prematurely,andpreventingtheoutputfromreachingregulation.  
If the ambient temperature is above 70 °C then a diode with  
trr 35 ns should be used.  
Feedback Resistors R1 and R3  
The values of the resistors in the resistor divider formed by  
R1 and R3 are selected to maintain 1.65 V at the FB pin. It is  
recommended that R3 be chosen as a standard 1% resistor of  
2kΩ. Thisensuresgoodnoiseimmunitybybiasingthefeedback  
network with a current of approximately 0.8 mA.  
For CCM an ultra-fast diode with reverse recovery time  
trr 35 ns should be used. A slower diode may cause excessive  
leading edge current spikes, terminating the switching cycle  
prematurely and preventing full power delivery.  
Feedback Capacitor C3  
Capacitor C3 can be a low cost general purpose capacitor. It  
provides a “sample and hold” function, charging to the output  
voltage during the off time of LinkSwitch-TN. Its value should  
be 10 μF to 22 μF; smaller values cause poorer regulation at  
light load conditions.  
Fast and slow diodes should never be used as the large reverse  
recovery currents can cause excessive power dissipation in the  
diode and/or exceed the maximum drain current specication  
of LinkSwitch-TN.  
7
Rev. I 11/08  
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