• Alternative FET recommendation for AD421

    I am using AD421BR on our transmitters as 4/20mA output IC. As stated in the
    AD421 datasheet;
    The DN25D FET transistor from Supertex1 meets all requirements for the FET.
    Other suitable FETs include ND2020L and ND2410L, both from Siliconix.

  • AD421 loop Current

    I use the top circuit for drive the AD421. To get the current of 4-20 mA, should an external power supply be used instead of  Vloop?
    And should be resistor series to an external power supply and the voltage across the resistor be the same as the current of…

  • AD421 data input interfacing with optocoupler

    how can i interface the AD420/1 digital inputs with optocouplers? Do you
    include Schmitt trigger on clock or data lines?


    We strongly advise that you use Schmitt triggers when interfacing the AD420 to
    opto-couplers. We have done extensive testing…

  • AD421 initial operational state after power up (all digital inputs tied low)?

    I do not use the DAC's functionality, only its 3.3V output to power the MODEM to communicate HART over the loop.

    I do not want to have to add circuitry to write the DAC's loop current register.

    What is the default loop current?

    Will a AD5700 HART…

  • AD421的环路电流建立时间



  • RE: AD421 instability

    This question has been closed by the EZ team and is assumed answered.
  • RE: ad421异常问题

    This question has been closed by the EZ team and is assumed answered.
  • AD421输出电流恒不变

      我使用了AD421。程序用三线模拟,硬件方面参考了中文规格书的电流源电路,其中没有用光耦,然后也没有用稳压源5V,电流输出LOOP RTN只接了一个1K的电阻出来。我使用的是外接电源5V给VCC,BOOST接VCC,VCC接4.7电解电容UF到地,LV接地,C1,C2,C3按规格书接了到COM,三根单片机的连线直接通过上拉10K 上拉到VCC接到STM32三根IO。



  • RE: AD421 HART Noise during silence

    In addition, I would like to ask another question. In the datasheet of the AD5421, I find that the reference circuit of the AD5421 has been verified and registered as an approved HART solution by the HART Communication Foundation.Does the reference circuit…