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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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FAN2513S25X Fiches technique(PDF) 4 Page - Fairchild Semiconductor |
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FAN2513S25X Fiches technique(HTML) 4 Page - Fairchild Semiconductor |
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4 / 10 page  PRODUCT SPECIFICATION FAN2512/FAN2513 4 REV. 1.1.8 5/25/04 Thermal Characteristics The FAN2512/13 is designed to supply 150mA at the speci- fied output voltage with an operating die (junction) tempera- ture of up to 125°C. Once the power dissipation and thermal resistance is known, the maximum junction temperature of the device can be calculated. While the power dissipation is calculated from known electrical parameters, the thermal resistance is a result of the thermal characteristics of the compact SOT23-5 surface-mount package and the surround- ing PC Board copper to which it is mounted. The power dissipation is equal to the product of the input-to- output voltage differential and the output current plus the ground current multiplied by the input voltage, or: The ground pin current IGND can be found in the charts provided in the Electrical Characteristics section. The relationship describing the thermal behavior of the package is: where TJ(max) is the maximum allowable junction tempera- ture of the die, which is 125°C, and TA is the ambient operat- ing temperature. θJA is dependent on the surrounding PC board layout and can be empirically obtained. While the θJC (junction-to-case) of the SOT23-5 package is specified at 130°C /W, the θJA of the minimum PWB footprint will be at least 235°C /W. This can be improved upon by providing a heat sink of surrounding copper ground on the PWB. Depending on the size of the copper area, the resulting θJA can range from approximately 180°C /W for one square inch to nearly 130°C /W for 4 square inches. The addition of backside copper with through-holes, stiffeners, and other enhancements can also aid in reducing this value. The heat contributed by the dissipation of other devices located nearby must be included in design considerations. Once the limiting parameters in these two relationships have been determined, the design can be modified to ensure that the device remains within specified operating conditions. If overload conditions are not considered, it is possible for the device to enter a thermal cycling loop, in which the circuit enters a shutdown condition, cools, re-enables, and then again overheats and shuts down repeatedly due to an unmanaged fault condition. Operation of Adjustable Version The adjustable version of the FAN2512/13 includes an input pin ADJ which allows the user to select an output voltage ranging from 1.32V to near VIN, using an external resistor divider. The voltage VADJ presented to the ADJ pin is fed to the onboard error amplifier which adjusts the output voltage until VADJ is equal to the onboard bandgap reference voltage of 1.32V(typ). The equation is: The total value of the resistor chain should not exceed 250K Ω total to keep the error amplifier biased during no-load conditions. Programming output voltages very near VIN need to allow for the magnitude and variation of the dropout voltage VDO over load, supply, and temperature variations. Note that the low-leakage FET input to the CMOS Error Amplifier induces no bias current error to the calculation. General PWB Layout Considerations To achieve the full performance of the device, careful circuit layout and grounding technique must be observed. Establish- ing a small local ground, to which the GND pin, the output and bypass capacitors are connected, is recommended, while the input capacitor should be grounded to the main ground plane. The quiet local ground is then routed back to the main ground plane using feedthrough vias. In general, the high- frequency compensation components (input, bypass, and output capacitors) should be located as close to the device as possible. The proximity of the output capacitor is especially important to achieve optimal noise compensation from the onboard error amplifier, especially during high load condi- tions. A large copper area in the local ground will provide the heat sinking discussed above when high power dissipation significantly increases the temperature of the device. Component-side copper provides significantly better thermal performance for this surface-mount device, compared to that obtained when using only copper planes on the underside. P D V IN V OUT – ()I OUT V INIGND + = P D max () T J max () TA – θ JA ------------------------------- = V OUT 1.32V 1 R upper R lower ---------------- + × = |
Numéro de pièce similaire - FAN2513S25X |
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Description similaire - FAN2513S25X |
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