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UC3578DP датащи(PDF) 6 Page - Texas Instruments |
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UC3578DP датащи(HTML) 6 Page - Texas Instruments |
6 / 11 page 6 UC2578 UC3578 UNITRODE CORPORATION 7 CONTINENTAL BLVD. • MERRIMACK, NH 03054 TEL. (603) 424-2410 FAX (603) 424-3460 0 5 10 15 20 25 30 0 10 203040 5060 7080 VCC (V) -55°C -25°C 25°C 85°C 125°C Figure 3. ICC vs. VCC vs. temperature. () Pd Qg kHz mA VIN =• + • 100 19 , (3) where Qg is the total MOSFET gate charge and 19mA is the maximum quiescent current for the UC3578 (ICC + IGG) from the data sheet. The switching frequency of the buck converter is 100kHz. The gate charge can be determined from the MOSFET data sheet. As an example, for a IRFZ34 which has a to- tal gate charge of 46nC, substituting for Pd in equation 3: () 0 95 46 100 19 . WnC kHz mA VIN =• + • , and () V= 0.95W 0.0236A = 40V IN max . Therefore, at 70°C using a IRFZ34 MOSFET the maxi- mum input voltage is limited to 40V to maintain a maxi- mum junction temperature of 125°C in the 16 pin DP package. Higher input voltages can be achieved by choosing a MOSFET with a lower total gate charge or by a reduced ambient operating temperature or by reducing the theta j-a of the package by improving the PCB mounting method. It is recommended that the four GND pins (4, 5, 12 and 13) be connected to a ground plane to provide a low resistance thermal path. If a ground plane is not available, a heat spreader on a double sided PC board is recommended. Note: Thermal impedance number is based on device mounted to 5 square inch FR4 PC board with one ounce copper. From Unitrode 95-96 data book Table 1, page 9-8, when resistance range is given, lower thermal im- pedance values are for 5 square inch aluminum PC board. ADDITIONAL INFORMATION Please refer to the following Unitrode topic for additional application information. [1] Application Note U-167, Design and Evaluation of a 48V to 5V Telecom Buck Converter using the UC3578 Control IC by Mark Dennis. APPLICATION INFORMATION (cont.) Not Recommended for New Designs |
Аналогичный номер детали - UC3578DP |
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Аналогичное описание - UC3578DP |
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