Question
We are designing a new system with a bus RS485, using ADM3075EARZ as driver. In
this system, not all the RS485 drivers are powered at all times, because they
don't have the same power supply. What happens with the bus impedance when one
or more driver are not powered? Is it affected the impedance of the bus because
one or more RS485 drivers are without power?
Answer
The unpowered ADM3075E will still be a load on the bus of 1/8th unit load (up
to 256 nodes possible). The impedance will be a minimum of 96 kOhm, powered or
unpowered.