Why Isolator Selection Deserves Care

A digital isolator passes a signal between two domains that must not share a ground, so its channel count, its isolation rating and its data rate set whether the interface is safe and reliable. Choosing too low an isolation rating or too few channels forces a change, and ignoring the common-mode transient immunity leads to data errors in a fast-switching system. This guide walks through a repeatable method for selecting a NOVOSENSE digital isolator.

Step 1: Count the Channels

Start with the signals that must cross the barrier. A simple UART or an isolated CAN needs two channels, an SPI bus or a group of control lines needs four, and a wider interface needs more. NOVOSENSE offers two-channel, four-channel and multi-channel parts, and some integrate an isolated DC-DC converter that also carries power across the barrier, so count the signals and decide whether the isolated side needs its own supply.

Channel Direction

A part can have the channels all in one direction or split between the two, so confirm the direction you need for the interface. A bidirectional bus such as I2C needs the channels in both directions, while a simple control path may need only one. Choose the part whose channel directions match the interface.

Step 2: Set the Isolation Rating

The isolation rating comes from the voltage difference between the two domains and the standard you must meet. A 3750 Vrms part suits a general industrial interface, and a 5000 Vrms part with a wider body gives the reinforced isolation and the creepage for a higher-voltage system. The package body sets the creepage and the clearance, so a wider body is chosen when the standard demands more distance across the barrier. Confirm the rating and the package together.

Reinforced and Basic Isolation

A reinforced isolation is required where a single fault must not defeat the barrier, and it needs a higher rating and a wider body than a basic isolation. Confirm which one the standard requires for your application, because it changes both the part and the layout.

Step 3: Match the Data Rate

Choose the data rate from the interface you must pass. NOVOSENSE isolators reach up to 150 Mbps, which covers an SPI bus, a fast UART and an industrial field bus, and a lower rate is enough for a simple control signal. Confirm that the host controller supports the rate and that the cables and the connectors do not limit it.

The Common-Mode Transient Immunity

The CMTI tells you how fast the grounds may move before the data is corrupted, and it is the key number for a fast-switching environment. A high CMTI, such as the hundreds of kilovolts per microsecond of the NOVOSENSE family, keeps the interface reliable in a motor drive or an inverter, so confirm it against the application.

Step 4: Confirm the Supply and the Package

Confirm the supply voltage against the two domains, because the two sides may run at different voltages, and confirm the package against the board. A small 8-SOIC suits a dense board, and a wider 16-SOIC gives more creepage for a higher-voltage system. Choose a part with the fail-safe output you need, so the output is defined when the input is not driven.

Step 5: Plan the Layout Across the Barrier

The isolation is only as good as the layout, so provide the required creepage and clearance under the package, keep the signal traces short on both sides, place the decoupling close to the supply pins of each side and use a ground plane on each side. Do not run a trace across the barrier, because a single trace defeats the isolation, and confirm the creepage against the standard you must meet.

Getting Help

If you send your signal count, the isolation rating and the data rate you need and the environment to our FAE team, we will propose an isolator, help choose the channel count and the supply scheme and review the layout. BeiLuo holds mainstream NOVOSENSE isolators in regional stock and ships them with an import declaration, a certificate of origin and a RoHS compliance file, and our engineers will review the choice with you before you commit to production.