ISO721-Q1

The ISO72x-Q1 is a digital isolator 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, this device prevents noise currents on a data bus or other circuits from entering the local ground and interfering with or damaging sensitive circuitry.

The capacitive isolation barrier conditions, translates to a balanced signal, then differentiates a binary input signal. 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 sent across the barrier ensures the proper dc level of the output. On failure to receive this dc refresh pulse for more than 4 µs, the response of the device is as if the input is or not actively driven, and the failsafe circuit drives the output to a logic-high state.

The symmetry of the dielectric and capacitor within the integrated circuitry provides for close capacitive matching and allows fast transient voltage changes between the input and output grounds without corrupting the output. The small capacitance and resulting time constant provide for fast operation with signaling rates⁽¹⁾ from 0 Mbps (dc) to 100 Mbps.

The device requires two supply voltages of 3.3 V, 5 V, or any combination. All inputs are 5-V tolerant when supplied from a 3.3-V supply, and all outputs are 4-mA CMOS. The device has a TTL input threshold and a noise filter at the input that prevents transient pulses of up to 2 ns in duration from being passed to the output of the device.

The ISO722-Q1 device includes 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 ISO72x-Q1 is characterized for operation over the ambient temperature range of –40°C to 125°C.