by making the connections on the outside of the chip instead of the ADUM1250
which connects the inputs and outputs inside the chip on each side?
No,you can not hook up an ADuM1400 to work like an ADuM1250. The ADuM1400 has
totem pole CMOS outputs. I2C requires an open collector type output. To
implement bidirectional communication two icoupler channels must be hooked
together each passing data in the opposite direction. If you just hook up the
channels like this it forms a latch. Even if you take care of making open
collector buffers, the first 0 that comes down the bus will latch the iCoupler
low and communication will stop.
If you want to use an ADuM1402 then you will have to add a special I2C buffer
available from NXP (Phillips), a P82B96 is popular for this application. The
exception to this is if you have an I2C bus with unidirectional lines instead
of a bidirectional lines. Power over Ethernet controllers do I2C this way
because they expect to be isolated. Even this will require some additional open