My Application circuit like this

I tested the voltage of IN1N,OUT1,and use the pin TMPGD drives a LED,

V(IN1N)= V(1N1P),V(OUT1)= V(IN2P),As 

I changed the valtage of TempSet  V(IN2P),Vout1 changed,according to the fomula,Rth changed,

but V(1N1N) still equals to Vref/2,As the voltage divider,

           V(IN1N) =Vref* (Rth+Rx)/(R+Rth+Rx)

V(IN1N) not changed,Rth Neither.

So it is  contradict.I can not understand.

Besides,when I tested the voltage of IN1N,the LED always twinkle. 

Thanks for your explaination.

  • 您好,希望这个能够帮到您

  • Hi ,

    Hope you are doing great.

    Based on what I can see, you are trying to check the chopper amplifiers functionality first. What I can suggest here is try to test the stage one by one and see if it is working. Example, try to test the chopper amplifier 1 first before connecting it to chopper amplifier 2. That way, it would be easier for you to identify if the stages are working. 

    However, on your circuit, what value of RFB did you use? can you share to me your actual schematic so I can check?


  • You may try disconnecting the chopper amp 1 first and test. disconnecting the chopper amp 2 and do test. how ever, when you test the chopper amp 2, the OUT2 will control the LDR and SFB output.

  • Thanks for your reply!

    The vlue of RFB is 80.6K. When I try to show my schematic,I can not find the upload option.I used  values of the Evaluation Board of ADN8834.

  • Hi @bai390529449,

    I see, you are using the evaluation board values. Are you using just the circuit values, or you are using the actual evaluation board?  

    I have here a clearer definition of the variables in the equation:

    VOUT1 = output of the chopper amplifier 1
    RTH = actual resistance of the thermistor AT A SPECIFIC TEMPERATURE
    RX = linearizing resistor
    R = RX + RTH (RTH @ the target (center) temperature)

    The linearizing resistor Rx and the RFB depends on the temperature range you want to maintain, and the corresponding thermistor resistance at those boundaries. the OUT1 output should swing from 0V to 2.5V (0.3V to 2.2V for practical values). from the evaluation board values, it will depend on the thermistor. Can you share what is your target temp range temperature  and the target temperature to be maintained? You should also know the corresponding thermistor resitance at the boundaries.  You may focus first on the chopper amplifier 1. On the evaluation board circuit, try disconnecting it first on the chopper 2 amp. To vary the IN1N voltage, try to heat and cool the thermistor, and observe the change in the OUT1 voltage. Once you're good, you can now proceed with the chopper amplifier 2.