Three-channel capacitive isolator for signal-chain galvanic separation
The Texas Instruments ISO7731FDBQ is a three-channel digital isolator using capacitive coupling technology to provide galvanic isolation across a 3000 Vrms barrier. It supports unidirectional data transmission at 100 Mbps across three channels configured as two on side 1 and one on side 2. With a propagation delay of 16 ns max and pulse-width distortion under 4.9 ns, this isolator suits timing-sensitive interfaces like SPI, UART, and general-purpose digital I/O where signal integrity across the isolation boundary matters. The 85 kV/µs common-mode transient immunity rating means it holds its state through fast voltage transients typical in motor drives, inverters, and industrial power stages.
The 100 Mbps data rate covers most digital interfaces used in industrial control — SPI clocks up to 50 MHz, UART at several Mbps, and parallel status lines. The 16 ns max propagation delay (same for rising and falling edges) adds about 32 ns round-trip to a handshake, which is negligible for most control loops but worth budgeting if the design closes a feedback path through the isolation barrier at high speed. Pulse-width distortion at 4.9 ns max keeps the duty cycle distortion low enough that the isolator won't introduce jitter that trips clocked receivers. The 1.3 ns rise and 1.4 ns fall times are symmetric, which helps maintain signal shape through the capacitive coupling stage.
Rated across the full military temperature range, the ISO7731FDBQ is specified for environments that see extreme thermal cycling: outdoor telecom cabinets, engine-bay electronics, downhole instrumentation, and avionics bays.