AGND Assistance

[Reigate]

I’m running a Teensy 3.2 and using a LT1009 as an external 2.5V reference as per the first circuit diagram in the 1009 data sheet.
http://www.analog.com/media/en/technical-documentation/data-sheets/1009ff.pdf

In regard to the ground, I have three choices but not sure which one is correct or I should use:
1. Ignore AGND and just run the reference ground tho the common Teensy ground;
2. Just run the reference ground to AGND; or
3. Run the reference ground to both AGND and the common Teensy ground?

I currently doing it as per option 1. but not sure this is the best method.

Any guidance would be appreciated.

 

[PaulStoffregen]

Usually #2 is best, if you can also connect whatever sensors or other analog circuitry you're using to AGND.

Otherwise, the other 2 are also ok.

Using AGND usually only helps if you also have something like LEDs with PWM or servo motors that use current which returns to GND. Keeping the analog AGND and digital GND currents on separate wires sometimes allows for better analog measurements. The key word is sometimes. In many other cases, it makes little or no difference.

Digital circuitry and modules which use substantial current should always connect to GND, not AGND.

 

[Reigate]

Thanks Paul.