Q
Are there any side effects when one side of the digital isolator is powered up
while the other side is powered down?
Are there any problems which can effect long term reliability, if for example
the input side is being powered and inputs driven high, while the output side
is off?
A
Each supply (VDD1 and VDD2) is completely independent - either can be operated
within data sheet limits or be powered down. Device operation in these various
states is shown in Table 11 in the ADuM1200 data sheet. Where one side of the
digital isolator is powered up while the other side is powered down the output
state will be as shown in Table 11.
In the case where VDD2 is unpowered , Voa and Vob output states will be
indeterminate since the output side is unpowered (as shown in Table 11). While
VDD2 is unpowered, the input side (VDD1) is still powered so there are internal
signals driven on the transformer primary windings in response to input
transitions or to send refresh states. These signals appear on the secondary
side and are rectified by parasitic elements, resulting in a small DC voltage
observed on the VDD2 supply (tests show this voltage can rise to about 0.9V and
can source 10's uA). This is normal and will not harm the ADuM1200