I've bought an LM39302R for my GSM module (SIM808):
The datasheet of the module recommends a Microchip regulator which is not available in my location so I've searched and found next best option, LM39302R, although I would be happy to find a cheaper replacement with acceptable voltage dropout.
Anyway, the LM39302R datasheet said it follows the famous rule of adjustable LDO regulator:
I built the PCB, and I've put 1K resistor on the top and 2.2K for R2 (I know VOUT trace of the regulator is too thin!)
According to the formulation which you can see in this online calculator it should be 4V on the white arrow on the PCB picture, but I read only 2 volts.
Why does this happen?
Almost all implementations use 100K resistor for R1 and 47K for R2. I don't see how it could output 4 volts, it should be 1.8375 volts.
The formulation has made me think, what is the difference if someone puts 1Kohm for R1 and 2Kohm for R2 or 1-ohm for R1 and 2-ohm for R2 or 1-Mega-ohm for R1 and 2-Mohm? Does it make any difference?
Any help would be appreciated!
It is a shame but the low voltage that I've read was because of a damage capacitor in the circuit! the value in the PCB picture which is recommended (100k and 47k) works fine and lm317 calculator values is almost the same for this chip.