STMicroelectronics has launched a family of high-end octal switches that combine galvanic isolation for robustness, RDS(on) below 260mΩ for power efficiency and protection, as well as diagnostics for reliability and fault recovery.
The 8-channel switches, ISO808, ISO808A, ISO808-1 and ISO808A-1, drive all types of industrial loads — capacitive, resistive and inductive — with one side connected to ground.
Typical uses are in programmable logic controllers (PLC), industrial PCs, and computer numerical control (CNC) machines — especially where isolation is needed to increase the protection of sensitive smart factory electronics.
ISO808 and ISO808A have a current limit of 0.7A, while ISO808-1 and ISO808A-1 have a limit of 1A. The ISO808 and ISO808-1 provide a separate input pin for each channel and allow direct control or synchronous operation by driving all outputs simultaneously.
The ISO808A and ISO808A-1 have an SPI serial input and feature an open drain power good (Pgood) indicator to assist with system management. All switches have a dedicated fault indicator pin.
Overload protection operates independently on each channel so that non-overloaded channels can continue to operate normally. Any overloaded channels are automatically shut down and restarted to enable quick recovery with minimal host intervention. The channel is turned off again if the fault persists, which is detected by monitoring channel and case temperatures.
There is also ground disconnect protection, reverse polarity protection, short circuit protection, thermal box protection, and undervoltage shutdown for the control-side (VDD) and process-side (VCC) power rails. Communications through the isolation barrier are via RF, which maximizes noise immunity. Internal logic reports any data errors and a watchdog ensures that the process stage outputs are safe if the control-side supply voltage is missing.
The performance and features of these switches help ensure that industrial applications meet applicable international standards, including IEC 61000 specifications for electrostatic discharge (ESD), electrical transients, and immunity to power frequency magnetic fields. They meet UL1577 and UL508 insulation specifications and VDE 0844-11 safety limits.
While pin compatible with other popular switches, ST's ISO808 family offers the extra benefits of lower RDS(on) and the good pin power of SPI input variants.
An extensive development ecosystem supports the ISO808 family, presenting an additional advantage over alternative devices. Four X-NUCLEO industrial digital output expansion boards (X-NUCLEO-OUT11A1, -OUT12A1, -OUT13A1, and -OUT14A1) for STM32 Nucleo development boards accelerate evaluation, while the graphical application, STSW-IFAPGUI, facilitates configuration and the control.
