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LM2940T-5.0 参数 Datasheet PDF下载

LM2940T-5.0图片预览
型号: LM2940T-5.0
PDF下载: 下载PDF文件 查看货源
内容描述: LM2940 -N / LM2940C 1A低压降稳压器 [LM2940-N/LM2940C 1A Low Dropout Regulator]
分类和应用: 线性稳压器IC调节器电源电路输出元件PC局域网
文件页数/大小: 35 页 / 2445 K
品牌: TI [ TEXAS INSTRUMENTS ]
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LM2940-N, LM2940C  
www.ti.com  
SNVS769I MARCH 2000REVISED APRIL 2013  
IIN = IL + IG  
PD = (VIN VOUT) IL + (VIN) IG  
Figure 36. Power Dissipation Diagram  
The next parameter which must be calculated is the maximum allowable temperature rise, TR(MAX). This is  
calculated by using the formula:  
TR(MAX) = TJ(MAX) TA(MAX)  
where  
TJ(MAX) is the maximum allowable junction temperature, which is 125°C for commercial grade parts.  
TA(MAX)is the maximum ambient temperature which will be encountered in the application.  
(1)  
Using the calculated values for TR(MAX) and PD, the maximum allowable value for the junction-to-ambient thermal  
resistance, θ(JA), can now be found:  
θ(JA) = TR(MAX) / PD  
(2)  
NOTE  
If the maximum allowable value for θ(JA) is found to be 53°C/W for the TO-220 package,  
80°C/W for the DDPAK/TO-263 package, or 174°C/W for the SOT-223 package, no  
heatsink is needed since the package alone will dissipate enough heat to satisfy these  
requirements.  
If the calculated value for θ(JA)falls below these limits, a heatsink is required.  
HEATSINKING TO-220 PACKAGE PARTS  
The TO-220 can be attached to a typical heatsink, or secured to a copper plane on a PC board. If a copper plane  
is to be used, the values of θ(JA) will be the same as shown in the next section for the DDPAK/TO-263.  
If a manufactured heatsink is to be selected, the value of heatsink-to-ambient thermal resistance, θ(HA), must  
first be calculated:  
θ(HA) = θ(JA) − θ(CH) − θ(JC)  
where  
θ(JC) is defined as the thermal resistance from the junction to the surface of the case. A value of 3°C/W can be  
assumed for θ(JC) for this calculation.  
θ(CH) is defined as the thermal resistance between the case and the surface of the heatsink. The value  
of θ(CH) will vary from about 1.5°C/W to about 2.5°C/W (depending on method of attachment, insulator, etc.). If  
the exact value is unknown, 2°C/W should be assumed for θ(CH)  
.
(3)  
When a value for θ(HA) is found using the equation shown, a heatsink must be selected that has a value that is  
less than or equal to this number.  
θ(HA) is specified numerically by the heatsink manufacturer in the catalog, or shown in a curve that plots  
temperature rise vs power dissipation for the heatsink.  
HEATSINKING DDPAK/TO-263 PACKAGE PARTS  
The DDPAK/TO-263 (KTT) package uses a copper plane on the PCB and the PCB itself as a heatsink. To  
optimize the heat sinking ability of the plane and PCB, solder the tab of the package to the plane.  
Figure 37 shows for the DDPAK/TO-263 the measured values of θ(JA) for different copper area sizes using a  
typical PCB with 1 ounce copper and no solder mask over the copper area used for heatsinking.  
Copyright © 2000–2013, Texas Instruments Incorporated  
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