I am using the Koala Proto Board. The schematic for the power supply on the board is missing some information. I would like to know the part number for the U4 IC. It looks like some kind of voltage regulator.
Thank you.
Sparkfun tend to use Micrel MIC5205 series voltage regulators.
http://www.micrel.com/_PDF/mic5205.pdf
Compare the part’s markings with the ones in the datasheet. It’s likely the part is labeled “KB33”…
You are correct, that is it.
I was mystified by the operation of this part. With no battery installed, the power to the LDO regulator comes from the battery charger. This measures 2.9V with a meter, but the LDO is putting out 3.3V. How could this be?
After some investigation, I discovered that the output from the battery charger is actually a pulsating voltage of up to 5V (2.9V is the avarage voltage). I had to use a scope to see this. So the LDO can provide an average 3.3V output (at least with no load).
This exercise was made more confusing because the schematic does not indicate a connection between the battery charger and the LDO regulator.
Now I know how the Koala board works. A couple of notes in the documents could have saved a lot of reverse engineering. But I wouldn’t have had as much fun. :?
Well it does… Be sure to follow the grey writing above some of the lines.
Top left corner of the schematic, you’ll notice how “VBATT” and “SW_VBATT” are connected together.
OK I see it now. When the USB is plugged in and the battery is switched on, the battery charger output provides the 3.3V power to the proto electronics via the LDO regulator. If a battery is connected, it is charged at the same time. If the battery switch is off, there is no 3.3V power to the proto electronics even when the USB cable is connected. (Unless 3.3V is taken directly from the USB IC instead of from the LDO regulator.)
Thanks!