The ISO721, ISO721M, ISO722, and ISO722M devices are digital isolators with a logic input and output buffer separated by a silicon dioxide (SiO2) insulation barrier. This barrier provides galvanic isolation of up to 4000VPK per VDE 0884-17. 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 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 provide the proper dc level of the output.

If this dc-refresh pulse is not received for more than 4µs, the input is assumed to be unpowered or not being actively driven, and the failsafe circuit drives the output to a logic-high state.Read more