Silicon Labs Debuts Si834x Family of Isolated Smart Switches for Industrial Applications

August 30, 2019 by Gary Elinoff

The new SiLabs units aim at the PLCs, relay drivers, and servo motor controllers employed in industrial automation.

The new SiLabs units aim at the PLCs, relay drivers, and servo motor controllers employed in industrial automation.

Silicon Labs’ Si834x isolated switches are designed to drive both resistive and inductive loads in harsh industrial environments. Members of this family of switches are all galvanically isolated via Silicon Labs’ CMOS-based isolation technology, sidestepping less reliable optocoupler-based isolation. This advance enables common-mode transient immunity (CMTI) of more than 100 kV/µs.


The Si834x. Image from Silicon Labs


The Si834x’s isolation technique is analogous to that of an optocoupler except that an RF carrier is modulated across the isolation barrier instead of light. This simple architecture provides a solid isolation path, requiring no special considerations or initialization during startup.


Block diagram representation of the Si834x illustrating the isolation barrier. Image from Silicon Labs


The Si834x provides four isolated high-side or low-side switches (sourcing or sinking). They feature RON (on-resistance) of 145 mΩ RON, and up to 700 mA of continuous current, compliant with the IEC 61131-2 standard.

The switch logic interface can be as basic as four low-power CMOS digital inputs or, alternatively, a full serial peripheral interface (SPI) capable of controlling up to 128 channels with four MCU pins.

Load Protection

Each individual switch can detect an open-circuit condition and is protected against over-current, over-voltage, and over-temperature conditions. The over-current protection includes an inrush current mode that allows the switch to drive loads that present challenges.

As described by Brian Mirkin, Vice President and General Manager of Silicon Labs’ power products, “The Si834x family expands our broad isolator portfolio, complementing our PLC input isolators and isolated FET drivers to provide a complete solution. The Si834x switches outperform opto-isolators, power FETs, and other competing options by offering a fully integrated 24 V digital output solution with best-in-class switch protection, flexible configuration, and comprehensive diagnostic feedback.”

The Members of the Si834x Family

All members of the Si834x family offer four output channels, offer a supply range of 9 volts to –32 volts, and can provide up to 0.7 amps continuous output current. Isolation is rated at 1.5 kilovolts VRMS.



While all the versions offer eight separate diagnostics reports, only those devices with the SPI interface (serial peripheral interface) allow access to all diagnostic and monitoring information via diagnostic registers. 

Devices without the SPI present diagnostics and monitoring information on active-low, open-drain indicator pins only. These pin outputs can be used to drive an LED to provide end-user feedback or they can be combined with a pull-up resistor and read by the controller.

This family of isolated smart switches operates over a temperature range of  -40°C to 120°C. They are offered in a 9mm by 9mm DFN-32 package.

Evaluation Kits

To enable users to get started more quickly on their designs, Silicon Labs has made evaluation kits available for all six extant Si834x isolated switches.


Si83404AAA Smart Switch Evaluation Kit: Image from Silicon Labs

Around the Industry

There are many manufacturers offering smart switches for both industrial and automotive applications.

As one example, the IPS4260L from STMicroelectronics is a quad (four-channel) low-side intelligent power switch. It can handle up to 0.6 amps on each channel, or 2.4 amps on a single channel. It sports an RON of 260 mΩ. This device is aimed at applications such as servo drivers, motor controls, industrial-PC peripherals, and PLCs.