Tool/software: WEBENCH® Design Tools
I'm working on a power supply based on the LM5122. Originally, the schematic was designed for 11v outputs from a 7.2v battery at probably 6A max.
For a smaller version, we need 12v at 500mA, so I was going to take the same design and scale down the board. However, the output transistors are enormous.
Going back, I figured the output transistors would only need to be rated for 1A for a rough doubling of voltage, and looked at 4A mosfets which were easy to find in a SOT-23 package and would provide what I thought would be plenty of overhead.
However, I went to WEBBENCH to see what TI would specify for a 6-8v to 12v 500mA supply. It gave the same schematic I currently have, with the exception of the drive transistors. For 12v at 500mA, my part options for output drivers were anywhere from 50-70 amps. This seems enormously excessive and adds about 20% to my board size. I checked the power dissipation which it showed at only 72mW, which works for the SOT-23 devices rated at 400mW - 1.2W.
Why would a 12v 500mA boost converter require 50A+ driver transistors? I didn't see much about this in the documentation. I'm still entry-level and I'm used to step-down converters, so any info about the operation of boost converters and this chip will be very helpful.
