Clean bipolar power from USBuss

[jackinnj]

This is pretty much the stock implementation of the LT3439 ultra low noise switcher -- promises maybe 100uV or less noise with the filters shown -- I use 70 uH with an 85kHz switching frequency -- only because I have a bunch of 70uH inductors laying around. I put a zener on the front input as the LT3439 is limited to 20V input -- the power supply could also be used in an automotive application. The drop resistor value is TBA.



The LT3439 is TSSOP so I had some boards made with a solder mask -- these should be back in a week or so. The LT3439 is cooled with the copper pour on the top surface. Resistors and caps are 0603, but I use through-hole electrolytics as they are so much easier to mount than smt's.