(sourcing the current) for the pins 13(VOB) and 14(VOA).
Page 4 of the ADuM1301 datasheet states that the test current is 4mA.
Furthermore, the output impedance of our devices are about 70ohms so, if the
load draws current, then the voltage at the output at a particular load is as
if the output was an ideal voltage source with a 70 ohm resistor in series.