Overview
An industrial or an automotive system often has two domains: a low-voltage controller and a higher-voltage or noisy field side. A digital isolator passes the signals between them without an electrical connection, so the controller is protected and the system is safe. NOVOSENSE builds its isolators on a capacitive barrier with a radio-frequency carrier, and BeiLuo supplies them with genuine traceability and FAE support. This page shows how the isolators cover an isolated interface.
Why Isolate an Interface
A field bus such as CAN, RS485 or SPI can sit at a ground potential that differs from the controller, and a fault, a surge or a long cable can inject a large common-mode voltage. A direct connection would then damage the controller or corrupt the data, so the interface is isolated. The isolator breaks the ground loop, blocks the common-mode voltage and keeps the signal clean, which improves both the safety and the reliability of the system.
Common-Mode Transient Immunity
In a fast-switching system the grounds move quickly, and a poor isolator turns that movement into an error. The NOVOSENSE capacitive isolator provides a high common-mode transient immunity, so the data crosses the barrier cleanly even when the two sides move by tens of kilovolts per microsecond, which is what a motor drive or an inverter imposes.
Choosing the Isolator
Choose the isolator from the number of signals, the isolation rating and the data rate. A two-channel part suits a simple UART or an isolated CAN, a four-channel part suits an SPI bus or a group of control lines, and a multi-channel part suits a wider interface. Choose the isolation rating from the voltage difference and the standard: 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. Confirm the data rate against the bus you must pass.
Integrated Isolated Power
Where the isolated side needs its own supply, a part with an integrated isolated DC-DC carries both the data and the power across one barrier. The NSIP9840 provides up to about 500 mW of isolated power with four signal channels, which removes a separate isolated supply and suits a compact design. Confirm the load current against the configuration you need.
Layout Across the Barrier
The isolation is only as good as the layout, so the design must respect the barrier. Keep the signal traces short on both sides, place the decoupling capacitors close to the supply pins of each side, and provide the required creepage and clearance under the package. Use a ground plane on each side and do not run a trace across the barrier, because a single trace that crosses defeats the isolation. Confirm the creepage against the standard you must meet.
Protection and Fail-Safe
Choose a part with the fail-safe output you need, so the output is defined when the input is not driven, and add the external protection that the standard requires, such as a transient suppressor on the field side. The isolator protects the controller, but the field side still needs its own protection.
Verification
Validate the design on the bench by passing the bus traffic at the worst-case rate, by imposing a common-mode step that matches the application and by checking the output for an error or a glitch. Measure the current on each side and confirm the isolated supply is stable. Our FAE team can review the layout and the measurements, so the isolation performs in the product as it does on the datasheet.
Getting Help
Send your signal count, the isolation rating and the data rate you need and the environment to our FAE team, and 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, so an isolated interface design can move from prototype to production without a supply gap.