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CS5253B-1 датащи(PDF) 9 Page - ON Semiconductor |
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CS5253B-1 датащи(HTML) 9 Page - ON Semiconductor |
9 / 10 page CS5253B−1 http://onsemi.com 9 capacitance and the input voltage is instantaneously shorted to ground, damage can occur. In this case, a diode connected as shown in Figure 22 is recommended. Figure 22. Diode Protection Circuit CS5253B−1 VCONTROL VPOWER VOUT VSENSE Adjust A rule of thumb useful in determining if a protection diode is required is to solve for current: I + C V T where: 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 typical short circuit current value provided in the specifications, serious thought should be given to the use of a protection 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 500 mA 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 circuitry has 25 °C of typical hysteresis, thereby allowing the regulator to recover from a thermal fault automatically. Calculating Power Dissipation and Heatsink Requirements High power regulators such as the CS5253B−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 heatsink is used. Since the package tab is connected to VOUT on the CS5253B−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 following four factors: junction temperature, ambient temperature, die power dissipation, and the thermal resistance from the die junction to ambient air. The maximum junction temperature can be determined by: TJ(max) + TA(max) ) PD(max) R qJA The maximum ambient temperature and the power dissipation 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 heatsink 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 components. These resistive terms are measured from junction−to−case (RqJC), case−to−heatsink (RqCS), and heatsink−to−ambient air (RqSA). The equation is: R qJA + RqJC ) RqCS ) RqSA The value for RQJC is 2.5°C/watt for the CS5253B−1 in the D2PAK−5 package. For a high current regulator such as the CS5253B−1 the majority of heat is generated in the power transistor section. The value for RqSA depends on the heatsink type, while the RqCS depends on factors such as package type, heatsink interface (is an insulator and thermal grease used?), and the contact area between the heatsink and the package. Once these calculations are complete, the maximum permissible value of RqJA can be calculated and the proper heatsink selected. For further discussion on heatsink selection, see our application note “Thermal Management,” document number AND8036/D. |
Аналогичный номер детали - CS5253B-1 |
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Аналогичное описание - CS5253B-1 |
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