SPI bus isolation — what the 40 Mbps and 14 ns propagation mean for your timing budget
The ADUM3150BRSZ-RL7 is a 6-channel unidirectional SPI digital isolator from Analog Devices' iCoupler SPIsolator series, using magnetic coupling to pass data across a 3750 Vrms galvanic isolation barrier. It is designed specifically for isolating SPI buses in industrial motor drives, grid-tied power converters, medical equipment, and any system where the controller and peripheral share different ground potentials or operate in different safety zones. The headline 40 Mbps data rate combined with a 14 ns max propagation delay gives this part enough timing margin to run SPI clocks up to 20 MHz or so without violating setup/hold windows, even after accounting for PCB trace delays and the isolator's 2 ns pulse-width distortion. The 2.5 ns rise/fall times keep the signal edges clean enough that you won't need schmitt-trigger buffers on short runs inside the same enclosure. Six channels with a 4/2 input split map naturally to the standard SPI signals: SCK, MOSI, MISO, and one chip-select on the controller side, with two channels available for interrupt or handshake lines on the peripheral side. The unidirectional architecture means each channel has a fixed direction — plan the signal assignment at layout time; you cannot reverse a channel on the fly.
25 kV/µs CMTI — surviving the switching environment
The 25 kV/µs common-mode transient immunity is the spec that matters when this isolator sits between a 3.3 V MCU and a gate-driver on a motor-drive phase leg. Every IGBT or SiC MOSFET switching event shoves a fast voltage step across the isolation barrier; if the CMTI rating is too low, the receiver sees a false data edge. At 25 kV/µs this part handles the dV/dt from a 600 V bus switching at 50 ns — typical for IGBT-based industrial drives — without bit errors.
Supply range and temperature — where it lives on the board
Both sides must be powered; there is no isolated power output, so each side needs its own local rail. In a motor-drive cabinet or outdoor telecom enclosure, the 125°C ceiling means no derating when ambient hits 85°C with self-heating from adjacent power components.
Package and footprint — 20-SSOP layout notes
The 20-SSOP package with 0.209 inch body width and 5.30 mm width is a common footprint shared with many ADI isolators. The supplier device package is 20-SSOP. Surface-mount assembly with standard reflow profiles;.
ROHS3 compliant.