поискавой системы для электроныых деталей |
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LM340A датащи(PDF) 8 Page - National Semiconductor (TI) |
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LM340A датащи(HTML) 8 Page - National Semiconductor (TI) |
8 / 15 page Application Hints (Continued) the output high can cause damage to internal low current paths in a manner similar to that just described in the “Short- ing the Regulator Input” section. Regulator Floating Ground ( Figure 2): When the ground pin alone becomes disconnected, the output approaches the unregulated input, causing possible damage to other circuits connected to V OUT. If ground is reconnected with power “ON”, damage may also occur to the regulator. This fault is most likely to occur when plugging in regulators or modules with on card regulators into powered up sockets. Power should be turned off first, thermal limit ceases operating, or ground should be connected first if power must be left on. Transient Voltages: If transients exceed the maximum rated input voltage of the device, or reach more than 0.8V below ground and have sufficient energy, they will damage the regulator. The solution is to use a large input capacitor, a series input breakdown diode, a choke, a transient suppres- sor or a combination of these. When a value for θ (H–A) 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 (H–A) is specified numerically by the heatsink manufacturer in this catalog, or shown in a curve that plots temperature rise vs power dissipation for the heatsink. HEATSINKING TO-263 AND SOT-223 PACKAGE PARTS Both the TO-263 (“S”) and SOT-223 (“MP”) packages use 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 plane. shows for the TO-263 the measured values of θ (J–A) for dif- ferent copper area sizes using a typical PCB with 1 ounce copper and no solder mask over the copper area used for heatsinking. As shown in the figure, increasing the copper area beyond 1 square inch produces very little improvement. It should also be observed that the minimum value of θ (J–A) for the TO-263 package mounted to a PCB is 32˚C/W. As a design aid, Figure 5 shows the maximum allowable power dissipation compared to ambient temperature for the TO-263 device (assuming θ (J–A) is 35˚C/W and the maxi- mum junction temperature is 125˚C). DS007781-8 FIGURE 1. Input Short DS007781-9 FIGURE 2. Regulator Floating Ground DS007781-10 FIGURE 3. Transients DS007781-39 FIGURE 4. θ (J–A) vs Copper (1 ounce) Area for the TO-263 Package DS007781-40 FIGURE 5. Maximum Power Dissipation vs T AMB for the TO-263 Package www.national.com 8 |
Аналогичный номер детали - LM340A |
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Аналогичное описание - LM340A |
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