0-5V acquisition with a 3.3V reference

[ARMinator]

Hi,

For several reasons, I am using a 3.3V MCU and I need to acquire 0-5V analog signals. To be within the 0-3.3V range, the 0-5V sensor inputs must then be multiplied by at most 3.3/5.

In these days where *most* MCUs run at 3.3V, I guess I'm not the only one to wonder about this problem. However, I've seen several similar posts on several forums that ended up with no answers...

I have been considering using a resistor divider, but this does not look like the ideal solution. The impedance of the divider will most likely interfere with the anti-aliasing filter and the impedance of the sensors.

I've turned to Amp Op circuits, but realized the solution is not as obvious as it seems. First the Amp Op must be in a non inverter configuration. My understanding of a non inverter is that the gain cannot be smaller than 1, if using a negative feedback. A gain smaller cab be achieved using the positive feedback of the Amp Op, however this can generate instability.

Could somebody recommend an Amp Op configuration that allow this? Even better, could somebody recommend a configuration that allow this, and include an anti aliasing filter?

Thanks!

 

[hameeds01]

simple use a Voltage divider
it will translate 0 to 5v into 0 to 3.3v

 

[kender]

Yep. Try a voltage divider.
Keep the resistor values low, if you can. Without knowing anything else, I would say about 2k. Add a 0.1uF cap from the middle of the divider to ground. That should lower the output impedance observed by the A/D.