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Question Regarding ADN8834s Chopper1 Amplifier Output


I am having trouble getting the ADN8834 to work as expected, and the cause appears to be coming from the Chopper1 amplifier. I am controlling the temperature by applying various voltages on the IN2P pin and OUT1 locks to this voltage; however, it does not match the relationship given by the equation for OUT1 in the datasheet. More specifically, increasing TEMPSET appears to decrease the temperature. I have tried to replace the thermistor with different resistors, and the OUT1 voltage increases as the resistance increases, which doesn't agree with the equations provided for calculating OUT1. The related component values that are being used and the measurements obtained by changing the resistance are given below.

Rth OUT1
9.95k 1.222V


Rx 7.47k
R 17.94k
RFB 71.4k

I have also used the ADN8834CP-EVALZ board and have gotten a similar response.

I tried to test the functionality of the amplifier by connecting it as a buffer (removing R,Rx,Z1, and replacing RFB with a short), but when applying 1.247V to IN1P, OUT1 is equal to 350mV.

I would appreciate any help I could get on understanding why the ADN8834 is not performing as expected.

Thank you in advance.

Top Replies

  • Hi ,

    Thanks for raising your concerns here. I would like to ask on few more details,

    • What is the VIN level you are using?
    • When you are measuring the OUT1 voltage with different values of Rth, is the OUT1 connected to OUT2 thru Z1?
    • If yes, what is the level of TEMPSET during that measurement?
    • Try removing Z1 before measuring OUT1 if it will change the measurement.

    Just additional info and comments:

    what you did in checking if the chopper 1 configuring it to buffer is good is correct. It should follow your IN1P voltage assuming everything is good. Kindly double check that everything is disconnected and the part is enabled. What I noticed with OUT1 = 350mV is that looks like the IN1P pin is pulled low to GND. 



  • Hey Noel,

    Thank you for your reply. The ADN8834 is now working as expected.

    The part was enabled through the enable pin; however, the problem seems to be VLIM/SD was connected to GND during the tests. I did not think this would affect the Chopper 1 amplifier.

  • Hi ,

    Good to hear! 

    That setting will bring the part in shutdown mode where both the chopper amps will not operate too.