I have a thermostat that outputs a DC power supply for a communication daughter board. When I read it with the voltmeter, it reads ~3.9v, but the zigbee module that I want to use requires 3.3v regulated.
Since its a tight squeeze inside the thermostat, I have to stick with SMD components. I looked at the the MCP1703 in the SOT-223-3 to do the job, but in the example schematic, the input voltage is 9v so I'm hesitant to use the 1uF input and output filter caps that they used.
Do I need an oscilloscope in order to do this right?
Can I just use the example caps even though my input voltage is ~3.9v rather than 9v?
How "clean" does my output voltage need to be for a typical zigbee module?
Best Answer
The MCP1703 requires 0.625V overhead to regulate a 3.3V supply when taking 250mA. This means it needs 3.925V for it to work correctly. However if you are only taking 25mA the drop-out voltage is more like 0.1V and this means you will be OK: -
There are more detailed graphs of other output voltages and their respective drop-out voltages but this one is closest to +3.3V
It'll work fine with the capacitors you specified - you just need to check what current your zigbee circuit might take under worst-case conditions. If in doubt make the regulator's output capacitance 10uF or larger but i don't think you'll need larger than 10uF