New Si838x Digital Isolator Outperforms Older Optocouplers in Factory Automation PLCs

Silicon Labs (Country Manager Baek Woon-dal) announced the launch of the industry's first high-speed, multi-channel digital isolator designed to meet the requirements of PLC (programmable logic controller) applications.

The new Si838x PLC field input isolator family combines high-speed channels (up to 2 Mbps), excellent channel density (up to 8 channels per device), bipolar input flexibility, high noise immunity, and 2.5k VRMS safety isolation. The Si838x family provides a functional solution suitable for industrial I/O modules, computer numerical control (CNC) equipment, and servo motor control. The company stated that the Si838x isolator is also suitable for process automation controllers (PACs) used in a wide range of process control systems.

PLCs deployed on factory floors in harsh environments must be robust and compact. Many PLC designs utilize up to 128 channels and feature multiple high-speed inputs. While optocouplers have provided a basic isolation solution for decades, they present significant challenges to PLC designers. Optos lacking high-speed performance are not fast enough for high-speed PLC applications such as servo motor control.

Opto solutions also lack high noise immunity, and as performance degrades over time and temperature, they pose reliability issues in high-temperature industrial applications. The Si838x family addresses these problems by being the first to provide a highly flexible, high-speed, multi-channel bipolar isolation solution in a small QSOP package, offering longer product life and higher reliability compared to opto-based solutions.

Silicon Labs' Si838x isolator is a highly integrated single-chip device that provides eight channels of 24 V digital field interfaces. This high level of integration significantly reduces the bill of materials (BOM) and board space in PLC designs. By utilizing 16 Si838x isolators in a “daisy-chaining” configuration in system designs, developers can design PLCs using up to 128 channels supported by a single serial peripheral interface (SPI) port on the system's embedded processor.

The controller interface can be configured with 8 channels or 4 ports of SPI in parallel. Developers can configure custom de-bounce for noise signals via SPI, and SPI can also be used for daisy-chaining to support high-density channel PLC designs. Selectable de-bounce filters can be pre-programmed via parallel configuration or programmed via serial configuration.

The Si838x isolator, featuring Silicon Labs' groundbreaking CMOS-based LED emulator technology, has flexible bipolar input capabilities that provide developers with a choice of sink or source inputs. The LED emulator input circuit supports up to eight sink or source inputs on the field side from a single isolator device without a power supply. The output interface to the controller supports 2.25V low-power operation.

The Si838x isolator provides 1 MHz (2 Mbps) high-speed performance essential for servo motor control applications. The isolator also offers industry-leading noise immunity on high-speed channels (50 kV/µs CMTI typical), which can improve system reliability.

Ross Sabolcik, Vice President and Head of Power Products at Silicon Labs, said, “Silicon Labs’ Si838x family solves unique challenges in PLC design by providing a compact, multi-channel, high-speed digital isolation solution. PLC developers can easily transition their optocoupler-based designs to state-of-the-art digital isolation technology that offers superior performance, excellent design flexibility, denser channel density, and long-term reliability.”