EEVblog Electronics Community Forum

Electronics => Beginners => Topic started by: Felicitus on January 17, 2014, 07:42:30 am

Title: MCP3426 ADC: Bipolar or not?
Post by: Felicitus on January 17, 2014, 07:42:30 am

Hi,

I'm having quite some trouble with the MCP3426 ADC (http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en545863). The datasheet says that it has an internal voltage reference of ±2.048V, so I first assumed that it can do bipolar measurements (at least in differential mode). Also, it implements signed output in the I²C protocol.

I have a few questions about this:

• The maximum differential voltage is specified as |V_dd-V_ss|. What do the | signs mean?
• The maximum rating for all inputs and outputs is specified as V_ss -0.4V to V_dd+0.4V. Do I assume correctly that this also includes the differential inputs?
• If I wanted to do positive and negative measurements, what would I have to do? Tie CH1- to 2.048V and use CH1+ for the input?

Title: Re: MCP3426 ADC: Bipolar or not?
Post by: fcb on January 17, 2014, 07:52:56 am

Differential input range is +/-2.048v.

These inputs are (as you point out) Vss-0.3v to Vss+0.3v. This means that you can't go to -2.048v with respect to 0V.

To solve the issue, either change your ADC or use a level shifter (that's what I would do - differential amplifier).