LT2986: Diode measurement

Hello 
I'm designing a temperature surveillance using LT2986.

According to the datasheet (Figure 8) a diode measurement can be done with a single channel or differential, using two channels.

  

From Datasheet:

Diode channel assignments follow the general convention
shown in Figure 8. The anode ties to CH
D (where D is
the selected channel number) for both the single-ended
and differential modes of operation, and the cathode is
grounded. For differential diode measurements, the cathode
is also tied to CH
D-1

The text specifies that in both cases, Cathode has to be connected to GND (makes sens).

  • What is the advantage of using differential mode?
  • Shall we add some Filter / Serie-Resistor... to the CH?
  • Or can we directly connect the diode to the input and get a good result?

Thank you for your answer

Kind regards
Botnic

  • 0
    •  Analog Employees 
    on May 15, 2020 8:27 PM 2 months ago

    Hi ,

        Differential mode has two advantages for diodes:

    1) If COM was tied to a different potential than GND for other sensors, using a differential reading for the diode ensures the voltage is sensed correctly. 

    2) If the ground connection between the LTC2986 and the diode had significant resistance and/or there were large ground currents - the ground potentials for the diode and the LTC2986 may differ. In that case, routing the diode signal differentially back to the LTC2986 would improve accuracy.

       To stay with the 2-conversion mode I would suggest only adding a small capacitance (100pF - 10nF). You can add series resistance but you must then use the 3-reading mode. The diode ends up being a fairly low impedance source so I would say unless you have a lot of interference in your environment you could probably directly connect and be fine. 

    -Logan