25 Mbps capacitive coupling — signal integrity across the isolation barrier
The ISO7240CFDWR: This is a 4-channel, unidirectional digital isolator using capacitive coupling technology, rated for a data rate of 25 Mbps. That speed comfortably covers SPI clocks up to 25 MHz, UART at any baud rate, and general-purpose isolated GPIO or control signals. Propagation delay is 42 ns max (tpLH / tpHL), with pulse-width distortion held to 2.5 ns max — tight enough to keep the duty cycle intact for PWM or timing-sensitive links. Rise and fall times are 2 ns typical, so the edges are clean without excessive ringing if you follow the usual 0.1 µF decoupling per supply pair.
The supply range spans 3.15 V to 5.5 V on both sides, so the same device can sit between a 3.3 V MCU and a 5 V peripheral without a separate level translator. Just tie each side's VCC to its respective rail — the capacitive coupling handles the level shift internally. The 2500 Vrms isolation rating is the standard for basic/reinforced isolation in motor drives, industrial PSUs, and medical equipment. Common-mode transient immunity is a minimum 25 kV/µs, which keeps the output from glitching during fast switching events on the isolated side.