Greetings mneary
The board will be vertical in still free air @ 30 degrees ambient, the ambient temp will be constant. From the Fairchild data-sheet: thermal resistance from junction to case is 12 degrees C per watt. Max junction temp is 150 degrees C. Referencing the transient response curve, transient resistance would be 0.2 for a single 1 second pulse. If I am understanding the math correctly a thermal pad that can dissipate 1 watt continuous would be able to dissipate a single 5 watt 1 second pulse. I would like to error on the safe side using 125 degrees C as the max. junction temp. and 35 degrees C as the ambient. What I do not have is a value that relates area to thermal resistance for a double sided 1 oz copper thermal pad to plug into the equation.
Greetings Boncuk
I much appreciate you posting the alternate layout. I am approaching this project as a learning opportunity. If someone does all the work for me that opportunity will be lost. I am using EAGLE 5.6.0 with custom package outlines, If you like, I can post the files. I will not be etching the board myself, so going double side is not an issue. Max. current would be at 1/2 Vss, ~330mA @ 6 volts.
How did you calculate the thermal rise for Q3? also your layout does not address several items I believe are important: 1) A low impedance ground path from J1 to J2 for load power, 2)The gate resistor for Q3 should be as close to the transistor as possible, 3) no trace for the FG signal.
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trident