Multi-channel PLC input isolators excel in factory automation

High-speed, multi-channel digital isolators by Silicon Labs are designed to meet the demands of PLC (programmable logic controller) applications. The Si838x PLC input isolators offer an unmatched combination of high-speed channels (up to 2Mbit/s), channel integration (up to eight channels per device), bipolar input flexibility, high noise immunity and 2.5kVRMS safety isolation.

The family is purpose-built for industrial I/O modules, computer numerical control (CNC) machines and servo motor control. They are also suitable for process automation controllers (PACs) used in distributed process control systems.

The isolators are offered in a compact QSOP, and has longer service life and higher reliability than opto-based solutions, says the company.

The integrated single-chip devices provide eight channels of 24V digital field interface, which enables significant bill-of-materials and board space savings in PLC designs. By “daisy chaining” 16 isolators in a system design, developers can create PLCs with up to 128 channels supported by a single serial peripheral interface (SPI) port on the system’s embedded processor.

The controller interface can be eight parallel channels or a four-port SPI. Developers can configure the SPI for on-the-fly programming for custom de-bounce of noisy signals and for daisy chaining to support high-channel-density PLC designs. An optional de-bounce filter is either pre-programmed in a parallel configuration or programmable in a serial-out configuration.

A bipolar input capability, based on the company’s CMOS-based LED emulator technology, gives a choice of sinking or sourcing inputs. The LED emulator input circuit supports up to eight sinking or sourcing inputs in a single isolator device with no power supply required on the field side. The output interface to the controller supports low-power operation with 2.25V operation capability.

The high-speed capability of 1MHz (2Mbit/s) is essential for servo motor control applications. The isolators also offer best-in-class noise immunity on high-speed channels (50kV/micros CMTI typical) to enhance system reliability.


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