Tiny Project: Positive to negative voltage with four parts
This is all about tiny projects and this one really takes it to the words: this is the smallets design I have ever done (and the quickest too). This is simply a very small implementation of the classical LMC7660 design. This circuit takes a positive voltage and converts it to a negative one that can be used in low-current applications. It is very useful in design involving operational amplifiers and there are no double power. The physical design of the PCB makes it useful like a module. With it's size of 10 x 18 mm, it is small enough to fit inside most designs. The actual reason I designed this thing was to correct an error in the Mini-ITX MiniMig design: the VGA buffer amplifier requires a negative voltage to operate correctly. I missed that part in the datasheet and fed the amplifier with +5V only, causing the VGA output to fail. This tiny module was designed to be mounted piggy-back on the amplifier IC, generating that missing -5V.

The design is really simple and follows the datasheet to the letter. Three capacitors (ceramic) and a SMD-version of the LMC7660 does the trick. The PCB is single sided with ground planes on both sides to reduce EMC. The schematics below shows the entire design:



And the boards:



The PCB-layout (in Protel DXP 2004 format) can be downloaded from this place. The ZIP-file contains both the single PCB-layout and the layout with six boards as one unit. Some PCB-manufacturers could have issues with designs that small. That's why I did the sixpack version.