EEVblog Electronics Community Forum

Electronics => Beginners => Topic started by: stevehendo on May 03, 2018, 04:18:27 am

Title: Using a DAC to control small voltages
Post by: stevehendo on May 03, 2018, 04:18:27 am

Hi All,

First time using a DAC, so feel free to set me straight if I am going about this all the wrong way.

I'm wanting to use a 12-bit DAC (MCP4725) to put out 5-50mV on the non-inverting input of an op amp (it's very low offset, so I think I'm ok in that regard).  I'm currently using a precision 5v reference (REF02).
 
I can see two options to get full resolution out of the DAC:

1) Use a 100 to 1 voltage divider (eg. 99k and 1k).  Is this reasonable or is there an upper limit to how high a voltage divider ratio can be?

2) Use the full 0-5V from the DAC and multiply the inverting input by 100 using a precision op amp.

Is there a preferred way to deal with this or am I way off track? Any advice much appreciated.

Steve

Title: Re: Using a DAC to control small voltages
Post by: ogden on May 03, 2018, 07:13:35 am

Voltage divider is most common way of altering DAC voltage range. Just make sure divider does not load DAC output. In your case MCP4725 is buffered with opamp output stage and does not mind (100k) load on it's output.

Title: Re: Using a DAC to control small voltages
Post by: stevehendo on May 03, 2018, 10:29:48 am

Thanks very much for your help.