The ADuM1250 is specified to drive 400pF. A 25m line is likely to have much
more than 400pF of capacitance (very roughly 2pF /cm so 2500*2 = 5000pF)
A 25m line will also couple large amounts of noise, e.g. from the SCL to the
SDA line, as well as from other RF interference, 50Hz etc etc.
Because of the low noise margin of 50mV, the ADuM1250 will be especially
vulnerable to noise pickup from long cables.. I think 25m with a single
AduM1250 is very risky.
RS-422 or RS485 are much more suitable physical layers (compared to I2C) for
covering 25m of cable. Our ADM2490E and ADM2491E , ADM2485 and ADM2486 are
RS-485 drivers Transcievers with iCoupler galvanic isolation