Isolated high-side switch for industrial automation designs

November 22, 2013 // By Graham Prophet
STMicroelectronics has introduced an octal high-side switch featuring integrated galvanic isolation, employing an RF communication technique through the isolation layer of ISO8200B ensures excellent levels of immunity to electromagnetic noise, in compliance with international standards and performing better than integrated devices featuring transformers.

As an integrated galvanic isolated switch, ST’s ISO8200B fulfils mandatory safety requirements and saves the space normally occupied by conventional opto-electronic isolation circuitry while also enhancing reliability. Energy-saving design ensures very low levels of quiescent current, thus reducing power dissipation by more than 10% compared to traditional, opto-coupler based solution. It is, ST says, the first galvanic-isolation high-side switch with pure RF communication, enabling savings in board space and power, with improved noise immunity.

Industrial switches require galvanic isolation, to protect the logic-controlled circuitry from disturbances on the power side, and to ensure user safety. Conventional, discrete optical isolators (opto-couplers) used for this purpose occupy additional pc-board space and are subject to aging and temperature-related degradation. ST says the switch is the first integrated device to combine galvanically isolated power and logic circuitry in the same package.

Inside the ISO8200B, separate logic and power chips are stacked with a layer interposer that provides very high isolation. The inputs are connected directly to a microcontroller or FPGA, and the device can drive eight output channels connected to any kind of load connected to ground, whether inductive, capacitive or resistive. The ISO8200B meets the RF immunity standard IEC 61000-4-3.

The design of the IC also ensures low quiescent operating current; the integrated power switch has very low on-state resistance. The ISO8200B integrates circuitry for fast demagnetization of inductive loads such as motors or heaters, which delivers further space and cost savings. Built-in protection features guard against over-temperature, short circuit, under-voltage, over-voltage, loss-of-ground or loss-of-supply voltage. In addition a fault output allows direct monitoring of correct operation.

Pricing is from $3.50 (1000).