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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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CS5257A-1GDP5 датащи(PDF) 8 Page - Cherry Semiconductor Corporation |
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CS5257A-1GDP5 датащи(HTML) 8 Page - Cherry Semiconductor Corporation |
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8 / 9 page  8 Application Notes: continued A rule of thumb useful in determining if a protection diode is required is to solve for current I= C ´ V , where T I is the current flow out of the load capacitance when VCONTROL is shorted, C is the value of load capacitance V is the output voltage, and T is the time duration required for VCONTROL to transition from high to being shorted. If the calculated current is greater than or equal to the typi- cal short circuit current value provided in the specifica- tions, serious thought should be given to the use of a pro- tection diode. Current Limit The internal current limit circuit limits the output current under excessive load conditions. Short Circuit Protection The device includes short circuit protection circuitry that clamps the output current at approximately two amperes less than its current limit value. This provides for a current foldback function, which reduces power dissipation under a direct shorted load. Thermal Shutdown The thermal shutdown circuitry is guaranteed by design to activate above a die junction temperature of approximately 150¡C and to shut down the regulator output. This circuit- ry has 25¡C of typical hysteresis, thereby allowing the reg- ulator to recover from a thermal fault automatically. Calculating Power Dissipation and Heat Sink Requirements High power regulators such as the CS5257A-1 usually operate at high junction temperatures. Therefore, it is important to calculate the power dissipation and junction temperatures accurately to ensure that an adequate heat sink is used. Since the package tab is connected to Vout on the CS5257A-1, electrical isolation may be required for some applications. Also, as with all high power packages, thermal compound in necessary to ensure proper heat flow. For added safety, this high current LDO includes an internal thermal shutdown circuit The thermal characteristics of an IC depend on the follow- ing four factors: junction temperature, ambient tempera- ture, die power dissipation, and the thermal resistance from the die junction to ambient air. The maximum junc- tion temperature can be determined by: TJ(max) = TA(max) + PD(max) ´ RQJA The maximum ambient temperature and the power dissi- pation are determined by the design while the maximum junction temperature and the thermal resistance depend on the manufacturer and the package type. The maximum power dissipation for a regulator is: PD(max) = (VIN(max) -VOUT(min))IOUT(max) + VIN(max) ´ IIN(max) A heat sink effectively increases the surface area of the package to improve the flow of heat away from the IC and into the surrounding air. Each material in the heat flow path between the IC and the outside environment has a thermal resistance which is measured in degrees per watt. Like series electrical resistances, these thermal resistances are summed to determine the total thermal resistance between the die junction and the surrounding air, RQJA. This total thermal resistance is comprised of three compo- nents. These resistive terms are measured from junction to case (RQJC), case to heat sink (RQCS), and heat sink to ambi- ent air (RQSA). The equation is: RQJA = RQJC + RQCS + RQSA The value for RQJC is 1.4ûC/watt for the CS5257A-1 in both the TO-220 and D2PAK packages. For a high current regu- lator such as the CS5257A-1 the majority of heat is generat- ed in the power transistor section. The value for RQSA depends on the heat sink type, while the RQCS depends on factors such as package type, heat sink interface (is an insulator and thermal grease used?), and the contact area between the heat sink and the package. Once these calcula- tions are complete, the maximum permissible value of RQJA can be calculated and the proper heat sink selected. For further discussion on heat sink selection, see our Cherry application note ÒThermal Management for Linear Regulators.Ó |
Аналогичный номер детали - CS5257A-1GDP5 |
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Аналогичное описание - CS5257A-1GDP5 |
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