After looking trough it some more, do at least 3 thing. First the capacitor C10 lose it shouldn't even be there you already have a lowpass filter made by R5 and C12, also the capacitor C12 feed automaticly brutal current change into the chip and add more current sensing capability from beyond the inductor, C10 make it lose that ability. Second add some small capacitor betweeen the pin 3 and 4 the closer the better it should help eliminating line noise. Third I'm not sure but on the datasheet schematic on page 10 they put a resistor between VCC and the diode probably for current limiting reason.
Hope that was helpful Timothy Miller wrote: >Here are images of the circuit diagram for the power supply circuit in >question, courtesy of our friends at gitk.com: > >A scaled and rotated version: >http://opengraphics.gitk.com/circuit_smaller.jpg >The original full-size image: >http://opengraphics.gitk.com/circuit.jpg > >The first image is probably most useful. We've spent about a week >trying to get this to work without success. > >First, we built it on copper clad but quicky realised that was not >going to work. Too much inductance in the high current carrying >connections led to all sorts of voltage spikes that upset the MAX8578 >IC. > >Then we built the circuit on a pre-existing blank circuit board with a >design similar to this. We knew the power on the existing board was >good, so we have a good idea that the layout is OK. We will provide a >sketch of the PC board layout when we get the chance. > >The new build of the circuit worked OK until we started loading the >circuit. When we attach a 0.5ohm load resistor, something in the >MAX8578 IC trips, and shuts off the output. From then on, it >continually tries to ramp up the output voltage (every 20ms or so) but >the output only gets to about 1.5V before the MAX8678 trips again. >We're running off a PC power supply, so there should be plenty of >juice to go around. > >We've tried a couple of ICs, different FETs, setting the over-current >protection really high and a few other things, but we get the same >results. > >We've spoken to a couple of apps engineers at Maxim, but they haven't >been able to figure out what we're doing wrong. > > >(Written by Howard, edited by Tim.) > >_______________________________________________ >Open-graphics mailing list >[email protected] >http://lists.duskglow.com/mailman/listinfo/open-graphics >List service provided by Duskglow Consulting, LLC (www.duskglow.com) > > > _______________________________________________ Open-graphics mailing list [email protected] http://lists.duskglow.com/mailman/listinfo/open-graphics List service provided by Duskglow Consulting, LLC (www.duskglow.com)
