Using ADUM6400 Vddl


I am trying to use the ADUM6400 isolation component with a LiIon battery. My Vcc is 3V for the rest of the circuit, however, for most power efficiency I would like to use the LiIon  voltage (4.2V) for Vdd. This poses a problem in that my logic levels are at 3.0V. The datasheet is not very clear about the use of Vddl, but it seems like this pin can be used to set the logic levels. But then I read that Vddi and Vddl must be connected to the same external supply.

Please clarify. Can Vddl be different from Vddi in order to for me to use lower voltage logic signals? If not, is there a workaround such that I don't have to regulate Vddi down to 3.0V before powering the ADUM6400.

Dave Rector

  • Hi Dave,

    The ADuM6400 added the extra Vddl pin to give a supply pin that was somewhat decoupled from the tank switching noise internal to the part, not to add a new feature.  We did not intend to have the supplies run at different volatges, so we have not characterized the device that way.

    I spoke to the priciple designer and he thinks there is nothing preventing the part from being operated with Vddl at 3V and Vdd1at 4.2V.  But it is not a configuration that we can guarentee performance, mostely because we have not checked it thoroughly.  I would give it a try.


  • Mark,

    Thank you for your help.

    Yes, indeed I hooked one up and tried it out.

    The logic output on the "non-isolated" side of an ADUM6402 seems to

    follow Vddl, and the inputs have thresholds that are also sensitive to

    this same level, and not Vdd1. It looks like this part will be able to

    do exactly what I need.

    Dave Rector


  • 0
    •  Analog Employees 
    on Aug 2, 2018 4:26 PM over 2 years ago
    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.

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