LM25085 Switching Regulator Design Calculator
The LM25085 is an affordable switching regulator in a small package, with a wide input voltage range. It's our experience that it's much better than the similar LM3489 which tends to run at too fast a frequency and overheat. The LM25085 has pad under it for better heat transfer. It also has very good design equations which are easy to follow, but tedious to implement by hand. This standard design uses the Vishay Si7465 P channel MOSFET, which has a low gate chare of only 40nC. The power disipation of the LM25085 is directly proportional to the gate charge of the MOSFET so this should be minimized.
R3 and C3 form a product. So you can scale them together. For example if you use a 0.01uF cap for C3 then divide the calculator's result for R3 by a factor 3.