What the ISO7731DBQ does on your board
The TI ISO7731DBQ is a three-channel digital isolator using capacitive coupling to pass digital signals across a galvanic isolation barrier. It delivers 100Mbps per channel with 16ns propagation delay and 4.9ns pulse-width distortion, which keeps timing margin clean for SPI, UART, and general-purpose logic isolation. The 3000Vrms isolation rating covers reinforced insulation requirements for industrial fieldbus, motor-drive feedback, and medical patient-interface separation. With 85kV/µs common-mode transient immunity, it handles the fast voltage slew rates in inverter and switching power supply environments without bit errors.
Three channels, two directions — routing the isolation barrier
The channel configuration is 2 inputs on side 1, 1 input on side 2 — all unidirectional. That maps cleanly to isolating a 2-wire SPI bus (SCLK, MOSI from the controller) plus a single feedback signal (MISO from the peripheral), or to breaking ground loops on three discrete control lines. The 2.25V to 5.5V supply range on each side lets you level-shift between 2.5V, 3.3V, and 5V domains without external translation. The 1.3ns typical rise/fall time preserves signal integrity at 100Mbps, but the fast edges also mean the PCB layout needs controlled impedance traces if the isolation channel runs more than a few centimetres.
The 16-SSOP package (3.90mm body width) fits compact multi-channel isolation modules without consuming excessive board area. No isolated power on-chip — you supply separate isolated rails on each side, which is the typical approach for discrete isolators in distributed systems.
Active lifecycle — no LTB concern
TI lists the ISO7731DBQ as Active. That means no last-time-buy risk for production programs currently qualifying it, and no pressure to redesign for a drop-in replacement. The base product number ISO7731 covers a family of channel-direction variants in the same 16-SSOP footprint, so if a design later needs a different channel mix (e.g., ISO7730DBQ with 3/0 direction), the PCB layout stays the same.