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