Galvanically isolated high-side switches protect industrial loads

The ISO808 switches from STMicroelectronics provide a wide range of protection functions against electrical and thermal faults. Development boards and configuration software ease integration of the switches into industrial equipment designs.

STMicroelectronics has launched a family of 8-channel high-side switches that combine galvanic isolation for robustness, low on-resistance for energy efficiency, as well as protection and diagnostics functions for reliability and fault recovery.

The ISO808 family of switches drives all types of industrial loads, capacitive, resistive, and inductive, with one side connected to ground. The switches are ideal for industrial machines in which isolation is needed to strengthen the protection of sensitive circuits in smart factory equipment.

The ISO808 and ISO808A have a current limit of 0.7 A, while the ISO808-1 and ISO808A-1 have a limit of 1 A. The ISO808 and ISO808-1 provide a separate Input pin for each channel, and allow either direct control, or synchronous operation in which all outputs are driven simultaneously. The ISO808A and ISO808A-1 have a serial peripheral interface (SPI) input, and feature an open-drain power-good indicator to aid system management. All switches have a dedicated Fault Indicator pin.

Overload protection operates independently on each channel, so non-overloaded channels can continue operating normally. Any overloaded channels are turned off and automatically restarted to permit rapid recovery with minimal intervention on the part of the host. The channel is shut down again if the fault remains: this is detected by monitoring channel and case temperatures.

The ISO808 high-side switches also provide various other protection functions for both the control- and the process-side power rails:

  • Ground disconnection protection
  • Reverse-polarity protection
  • Short-circuit protection
  • Thermal case protection
  • Under-voltage shut-down

Communication across the isolation barrier is by RF, which gives good noise immunity. Internal logic reports any data errors, and a watchdog ensures the process-stage outputs are safe if the control-side supply voltage is missing.

A graphical design tool, the STSW-IFAPGUI, eases configuration and control.

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