What the SPI type and isolated power mean for your BOM
The SI83405BDA-IF is an isolated smart switch with an SPI interface — not a general-purpose digital isolator. The SPI type means it integrates a serial peripheral interface controller on the isolation barrier, so a single SPI bus line from the host MCU controls the switch state without dedicated GPIO pins. Magnetic coupling technology provides the isolation barrier, rated at 1500Vrms. This is sufficient for basic isolation in 24V industrial control systems but not for reinforced mains isolation — the working voltage rating should be confirmed against the application's safety standard. The common-mode transient immunity of 100kV/µs ensures the output stays latched during fast voltage transients common in motor-drive environments.
Single-channel architecture and supply rails
This is a single-channel device with one input on side 1 and zero inputs on side 2 — the SPI command goes in, the switch state comes out on the isolated side. The propagation delay of 3.5µs (tpLH) and 4.5µs (tpHL) max means the switch responds within a few microseconds of the SPI command, suitable for relay or solenoid control where sub-millisecond timing is not critical. The dual supply range accepts 2.25V to 5.5V on the logic side — compatible with 3.3V and 5V MCU rails — and 9V to 32V on the power side, covering standard 12V and 24V industrial supplies.