What this digital isolator does — and who specifies it
The Texas Instruments ISO7420D is a two-channel, unidirectional digital isolator using capacitive coupling to pass signals across a 2500 Vrms isolation barrier. It sits between a microcontroller's UART or SPI port and a sensor, motor-drive gate driver, or isolated power-stage controller — any place where you need to break ground loops or protect logic from high-voltage transients without losing signal integrity. Both channels drive from Side 1 to Side 2 (2/0 input count), so this part handles a one-way data path: e.g., SPI clock + data out from the MCU to an isolated ADC, or a pair of control signals to a relay driver. Data rate is 1 Mbps, which covers 1 MHz SPI, standard UART baud rates up to 1 Mbaud, and most slow-to-moderate-speed digital interfaces. Propagation delay is 14 ns max each way — tight enough that timing margin isn't a concern at this speed. Rise and fall times are 1 ns typical, giving clean edges without excessive ringing on short PCB traces. This lets you interface a 3.3 V MCU domain to a 5 V peripheral domain — common in industrial I/O, PLCs, and motor drives — without a separate level shifter. The part does not include an integrated isolated DC-DC converter, so you must provide isolated power to each side separately. That covers factory floors, outdoor telecom cabinets, engine bays, and most HVAC controllers. Common-mode transient immunity is rated at 25 kV/µs minimum, which is enough for motor-drive and inverter environments where fast-switching IGBTs or SiC FETs generate high dV/dt on the bus.
At 1 Mbps, the ISO7420D is not a high-speed isolator — it won't carry 50 Mbps SPI or full-speed USB. But for the vast majority of industrial serial links (UART at 115200 baud, SPI at 1 MHz, I2C at 400 kHz) it has comfortable margin. The 14 ns propagation delay is negligible relative to a 1 µs bit period. If your design needs to push 10 Mbps or more, step up to the ISO7420FEDR (50 Mbps) or ISO7221CDR (25 Mbps) — both pin-compatible in the same 8-SOIC footprint.
2500 Vrms isolation — is it enough?
2500 Vrms is the basic isolation rating for this class of SOIC-8 digital isolator. It satisfies reinforced isolation requirements for most industrial equipment (IEC 60950-1, IEC 61010-1) as long as the working voltage stays within the derating curves. For 400 VAC motor drives or medical equipment needing 5 kV+ isolation, look at the ISO7830DWWR (5700 Vrms) in a wider SOIC-16 package — but that part is overkill and larger for a simple two-channel link.
That means no last-time-buy window looming, no end-of-life risk for the foreseeable future.
Sourcing and availability
For tube quantities (50 per tube) or reel, submit an RFQ through the storefront. If you need a faster data rate or a different channel direction configuration, the ISO7420FEDR (50 Mbps, same footprint) is a direct alternative worth cross-shopping.