Active production — BOM-fit for a 4-channel unidirectional isolator
The SI8040AA-B-IU is an active-production general-purpose digital isolator from Skyworks Solutions, built on capacitive coupling technology. It provides four unidirectional isolation channels in a 16-QSOP package, all inputs on side 1 (4/0 configuration), making it a direct fit for applications where the isolated side needs no return data path. The 10 Mbps data rate covers SPI and UART links at moderate bus speeds.
What the 10 Mbps and 35 kV/µs CMTI mean for your bus
The 10 Mbps data rate is the maximum guaranteed toggle rate across the isolation barrier — at this speed the 65 ns max propagation delay and 30 ns pulse-width distortion still leave enough timing margin for a 20 MHz SPI clock (50 ns period) to be recovered cleanly on the secondary side. Below 10 Mbps the timing margin widens further. Common-mode transient immunity of 35 kV/µs means the output does not glitch when a 1 kV/µs step appears across the isolation barrier — a realistic condition in a motor-drive inverter where the IGBT switching node slews at several kV/µs. This CMTI figure is typical for capacitive-coupled isolators in this class and is adequate for most industrial inverter and servo drive applications. The 2.5 ns typical rise/fall time means the output edges are fast enough to drive standard CMOS logic inputs without extra Schmitt-trigger buffering, but the fast edges also couple more noise onto the PCB than a slower isolator — keep the output trace short and avoid routing it near sensitive analog lines.
Supply rails and temperature grade
No isolated DC-DC converter is integrated — the SI8040AA-B-IU provides signal isolation only. The secondary-side circuitry requires its own local supply rail, typically derived from a separate isolated DC-DC module or a bias winding on the system power supply.
Package and board-fit note
Supplied in tube packaging (standard for prototype and low-volume assembly). The 16-QSOP body is 3.90 mm wide — a narrow SOIC derivative with 0.635 mm pin pitch. The footprint is compatible with standard 16-pin SSOP (3.90 mm) land patterns. Surface-mount reflow profile follows standard MSL for this package class; no special moisture-sensitivity bake is required unless the tube seal has been compromised.
Peer comparison — SI8035AA-B-IU vs SI8040AA-B-IU
The closest functional sibling is the SI8035AA-B-IU, which shares the same package, data rate, isolation voltage, propagation delay, CMTI, and temperature grade. The difference is channel count: the SI8035 provides 3 unidirectional channels (3/0 configuration) versus the SI8040's 4 channels (4/0). A board originally laid out for the 3-channel part can accept the 4-channel SI8040 if the fourth input is left unconnected or tied to a logic level — the pinout is the same, only the extra channel is added.