The ISO721, ISO721M, ISO722, and ISO722M are digital isolators with a logic input and output buffer separated
by a silicon oxide (SiO2) insulation barrier. This barrier provides galvanic isolation of up to 4000 V. Used in
conjunction with isolated power supplies, these devices prevent noise currents on a data bus or other circuits
from entering the local ground, and interfering with or damaging sensitive circuitry.
A binary input signal is conditioned, translated to a balanced signal, then differentiated by the capacitive isolation
barrier. Across the isolation barrier, a differential comparator receives the logic transition information, then sets or
resets a flip-flop and the output circuit accordingly. A periodic update pulse is sent across the barrier to ensure
the proper dc level of the output. If this dc-refresh pulse is not received for more than 4 ms, the input is assumed
to be unpowered or not being actively driven, and the failsafe circuit drives the output to a logic high state.