LT2986: Diode measurement

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

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

  • 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.