ISO721D

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.

These devices require two supply voltages of 3.3V, 5V, or any combination. All inputs are 5V tolerant when supplied from a 3.3V supply and all outputs are 4mA CMOS.

The ISO722 and ISO722M devices include an active-low output enable that when driven to a high logic level, places the output in a high-impedance state and turns off internal bias circuitry to conserve power.

The ISO721 and ISO722 devices have TTL input thresholds and a noise filter at the input that prevent transient pulses of up to 2ns in duration from being passed to the output of the device.

The ISO721M and ISO722M devices have CMOS VCC / 2 input thresholds, but do not have the noise-filter and the additional propagation delay. These features of the ISO721M device also provide for reduced-jitter operation.

The ISO721, ISO721M, ISO722, and ISO722M devices are characterized for operation over the ambient temperature range of –40°C to +125°C.