I'm working on the design of a buck switcher which will charge a 12 volt battery bank. The problem I'm having is with the low side MOSFET which I'm using for synchronous rectification -- it's immediately destroyed whenever the supply is turned on with a battery connected to the output. Upon scrutinizing the schematic, I can see why -- the synchronous MOSFET places a direct short across the battery when it is switched on. The design is a common one centered around a LT1339 driver, with both MOSFETS being N-type IRFZ48, but after searching the Web for hours, I can find no mention of this problem. How is it possible to use synchronous rectification with a battery that can easily back-feed hundreds of amps of current through the low side MOSFET without placing a diode on the output?
Sorry, too vague to get a coherant answer without a schematic to compare. [Student looking for a free ride??]
