SparkFun Forums

[mohrens]

I got a power supply problem that is caused by theBluetooth v2.0 DIP Module.
Using a 3.3 voltage regulator (MCP1700) and a PIC on the board
as soon as I add the DIP Module I get a about .2V oscillation at about 2-3Hz on Vdd.
I have lots of caps for decoupling ...

Any ideas would be appreciated

[wiml]

Is it a smooth oscillation or is it that the bluetooth module is drawing current in pulses? Lots of digital radios have very pulse-y current demands ... you might just need a stiffer/faster regulator.

[marcovansteen]

load regulation of mcp1700 is +/-1.5% worst case
This can explain +/-50mV jumps in the signal due to changing load currents (if load changes from 0.1 .. 250mA)

So I don't think that load regulation is the problem.

Three more possible causes to check:
1) do you have enough dropout voltage? The input voltage must be at least 0.2V above the output voltage.
2) is the chip getting hot? If so, it may go into shutdown 2 or 3 times per second once it has to deliver power. This is a very small package so good heatsinking is needed.
3) maybe the output cap is too large for stability? remove caps, try again.

anyway: if you didn't do it, rtfds : http://ww1.microchip.com/downloads/en/D ... 21826b.pdf

Good luck!!

Marco