AD5421 Powering up



I have design AD5421 based 4-20mA loop powered system. The schematic is attached. I see following problem:

1. The D_VDD always outputs 4.2V but datasheet says 3.3V but can have 5.5V overdrive.

2. If REG_OUT pin floating instead of tying to D_VDD and IOD_VDD and measure voltage at REG_OUT then it measures 2.7V.

The REG_SEL0 and REG_SEL1 is tied to 3.3V and REG_SEL2 is tied to GND.

3. The range resistors are tied to ground to configure output to 4-2mA.

4. The ADuM1447 is disconnected from the system.


Could anyone guide me what is wrong happening? Did I miss anything?



  • Hi Michael,

    Thanks for your reply.

    To answer some your question, I did not programmed the Micro. So the data lines to DAC were pulled high.

    There are couple of things I found and I fixed it and now the DAC has correct voltage.

    1. Initially I tied REG_OUT and D_VDD  together.

    2. The reference to DAC had potential almost 1V above ground.



  • 0
    •  Analog Employees 
    on Aug 2, 2018 3:23 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

    Thank you,
    EZ Admin