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UC3578DP Datasheet(PDF) 5 Page - Texas Instruments |
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UC3578DP Datasheet(HTML) 5 Page - Texas Instruments |
5 / 11 page 5 UC2578 UC3578 MOSFET and result in startup problems with the regula- tor. A Schottky rectifier is used for the free-wheeling di- ode to limit the negative excursion of the source. This will also limit the reverse recovery current thus limiting the in- ductive voltage spike. In applications where transient load excursions may re- sult in a no load condition, it is necessary that the output of the regulator be loaded with a small load current (10mA to 15mA). This will prevent the output voltage from going unregulated at no load. This small load cur- rent is necessary for proper operation of the floating driver since the source must fly low to charge up the floating driver capacitance. Thermal Considerations For proper operation and reliability of the UC3578, proper thermal management is essential. It is important that the designer keep in mind that with surface mount packages, a significant amount of the heat that the de- vice generates is conducted out through the lead frame. Because of this, the PCB design becomes a critical part of the thermal management system. Worst case junc- tion-to-ambient thermal resistance for different package configurations are given in a table in the data book in the package information section. The maximum ambient operating temperature is an im- portant factor in determining what the maximum operat- ing voltage can be for a particular application. For example, if we assume a maximum operating ambient temperature of 70°C we can determine what the maxi- mum allowable input voltage can be given other parame- ters such as package thermal impedance and MOSFET total gate charge by following the procedure outlined be- low; () TT C C C J A max –– =° ° = ° 125 70 55 . (1) Pd = 55 C 58 C / W = 0.95W ° ° , (2) where 58°C/W is the worst case theta j-a for the 16 pin DP package and Pd is the package power dissipation. 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 1 µF 470pF 0.1 µF 0.01 µF 1N4148 N/C EAINV EAOUT GND GND SRC OUT N/C SS CS VCC GND GND DIODE VGG N/C UC3578 330 0.1 µF 0.1 µF 8.25k 5.62k 2200 µF 2200 µF 680pF 51 1 2 10 30 µH 470 200 13 1N4148 5 220 µF 220 µF V IN(–) V IN(+) 15k TIP47 1N4745A 47 µF 47k 2200pF 100pF 2 3 1 HS3 23 1 HS1 IRF530 V OUT(–) V OUT(+) HS1, HS2, HS3: HEATSINKS HS2 MBR10100 Figure 2. Detailed application schematic for the UC3578 evaluation board. APPLICATION INFORMATION (cont.) UDG-99100 Not Recommended for New Designs |
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