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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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FAN2564 Fiches technique(PDF) 9 Page - Fairchild Semiconductor |
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FAN2564 Fiches technique(HTML) 9 Page - Fairchild Semiconductor |
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9 / 13 page  © 2007 Fairchild Semiconductor Corporation www.fairchildsemi.com FAN2564 • Rev. 1.0.2 9 Application Information Enable and Soft Start A 1.4 M pull-down resistor ensures the EN pin to be in LOW state when it is floating. The chip is in shut-down mode when EN pin is LOW. To enable the chip, the EN pin needs to be raised higher than 0.95V. The output pin starts to charge up to the final voltage. On-chip soft-start circuitry limits the peak inrush current through VIN pin to less than the specified typical value of 500mA, regardless of COUT value and load con- ditions. The startup time increases as VOUT, COUT, and load in- creases, but meets the specified 100µs under the worst load and VOUT conditions. Short-Circuit and Thermal Protection The output current is short-circuit protected. When a short-circuit fault occurs, the output current is automati- cally limited and VOUT drops, depending on the actual short-circuit resistance. Short-circuit fault or output overload may cause the die temperature to increase and exceed maximum ratings due to power dissipation. In such cases, depending upon the ambient temperature; VIN, load current, and the junc- tion-to-air thermal resistance (θJA) of the die; the device may enter thermal shutdown. When the die temperature exceeds the shutdown limit temperature, the onboard thermal protection disables the output until the temperature drops below its hysteresis value, at which point the output is re-enabled and a new soft-start sequence occurs as described above. Thermal Considerations For best performance, the die temperature and the pow- er dissipated should be kept at moderate values. The maximum power dissipated can be evaluated based on the following relationship: JA A (max) J (max) D T T P (1) where TJ(max) is the maximum allowable junction tempera- ture of the die and TA is the ambient operating tempera- ture. θJA is dependent on the surrounding PCB layout and can be improved by providing a heat sink of sur- rounding copper ground. The addition of backside copper with through-holes, stif- feners, and other enhancements can also aid in reducing θJA. The heat contributed by the dissipation of other de- vices located nearby must be included in design consid- erations. Capacitors Selection The FAN2564 is stable with a wide range of capacitor values and sizes. For loop stability, a 1µF input capacitor or bigger is rec- ommended. Tolerance, temperature, and voltage coeffi- cients of the capacitor must be considered to ensure effective capacitance stays around 1µF or above. There is no special requirement on its ESR value. An output capacitor with an effective capacitance be- tween 1µF and 10µF is required for loop stability. The ESR value should be within 5 to 100m . 2.2µF or 4.7µF ceramic capacitors are recommended to ensure stability over the full temperature, input, and output voltage range of operation, such as those listed in Table 1. Table 1. Recommended Capacitors Capacitance Size Vendor Part Number 1 F 0603 MURATA GRM188R71C105KA120 2.2 F 0603 MURATA GRM188R61A225KF340 2.2 F 0402 MURATA GRM155R60J225ME15 4.7 F 0603 MURATA GRM188C80G475KE19 4.7 F 0402 MURATA GRM155R60G475M |
Numéro de pièce similaire - FAN2564_11 |
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Description similaire - FAN2564_11 |
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