AD620, digitally adjusted reference pin


I use AD620 in order to amplify my loadcell signal. I have +/-15V present. I regulate these voltages to 10V and -11V. I use 10V to excite loadcell. Also I use 10V to power AD620 and OP177 op-amps. (There is a filtering circuit after AD620 with couple of OP177's). I use -11V to power OP177 and AD620.
With a help of a POT between -11V and zero volts I adjust reference pin voltage of AD620. I use OP177 to buffer POT.

My problem is that I need to change this system and put digitally adjustable reference pin voltage.

I am planning to use AD7391. BUT I need extra 5V supply. This supply must be very pricise I think. Right now I have a precision 10V source. How can I use this to power AD7391. Also I need opto-coupler to control AD7391.

AD7391 consumes around 100uA, optocouplers can be around couple of mA. Can I just use reference IC without boosting the output.

  • Hello miguel,

    I have in stock. And using that DAC for a long time for other projects.

    I think opto-coupler needed because the circuit that controls the DAC is very noisy. That circuit also controls motors. I do not want to connect grounds of this circuit with the AD620 circuit.



  • May I ask the reason behind using the AD7391?

    And opto-coupler, why?



  • Hi DC,

    For the reference IC, I would recommend ADR435 which has an output voltage of 5V, output accuracy of +/- 2mV (B grade) and a temperature coefficient of 3ppm/C. It has a wide operating range (7V to 18V) and would suit your design perfectly as you are using 10V supply.The ADR435 has the capability to source up to 30 mA of output current.

    I have suggested the ADR435 in the assumption that the opto-couplers (one opto-coupler per digital line) that you are going to use in the design will have around 5mA of current consumption. If you would like for your system to have lower power consumption, I would recommend looking into ADI's digital isolator portfolio (i.e. ADUM2400, at 5V operating supply, has 1.0 mA per channel maximum up to 2 Mbps).