We are back in the workshop from the Bay Area Maker Faire, expect our full report to start tomorrow.
We continue the work on the Part Ninja firmware. We implemented part specific functions for many parts. These functions figure out the pinout, and calculate part specific values, like the forward voltage for Diodes, hFE for transistors, resistance for resistors etc…
The buck-boost dc-dc converter is nearing completion. We are currently designing the over-voltage protection.
In the office we continue to do bookkeeping and filing for 2012.
Why not use a P-channel FET instead of an N-channel FET as Q4? With the posted schematics, you must have a higher voltage than SWV50 to drive the SMPS_BUCK signal. The negative end of R18 should also be moved from GND to the node Q4S-D5C-L2.
Select a fast Schottky diode as D4 and make sure that the Vds rating of Q3 has a good margin. Short transients of higher voltage might be present at Q3D if not D4 opens up fast enough and can cause breakdown of Q3.
I realized this after soldering the above circuit. I am not getting my requested output levels. After a short search, I realized that indeed the N-channel MOSFET is my problem. I will switch to a P-channel one and do the required changes.