Isolation Improvements Speed Manufacturing Automation

[Sanchita]

Isolation Improvements Speed Manufacturing Automation

By

Mark Morgan

Technologist, CTO Advanced Development

Texas Instruments

and

Giovanni Frattini

Kilby Labs Design Center Manager, Milan

Texas Instruments

========================================================================================================

All areas of electronics depend on galvanic isolation for safety, equipment protection and signal integrity. Today isolation is especially significant in industrial environments, which are rapidly increasing intelligent automation. Sensors, actuators, motors, robots, control units and other factory equipment must be protected from power irregularities and shielded from signal interference in order to operate reliably. Isolation is key to achieving these goals.

To deal with the increasing demands for safety and robust reliability, equipment makers are demanding more sophisticated isolation solutions from integrated circuit (IC) suppliers. Among the most important innovations is the use of integrated capacitors as isolators in ICs, which are packaged in multichip modules (MCMs). Using such isolation products, system manufacturers can create better-protected circuitry for power, communications and control. These systems, in turn, help distribute intelligent automation throughout the factory floor, bringing higher quality, cost control and energy efficiency, along with increased worker productivity and safety.

The Need for Isolation:

Isolation is a means of preventing direct current and unwanted alternating currents from passing between different parts of a system while allowing signal and power transfer. As the word suggests, isolation means the physical separation of one part of a circuit from another via a transformer, capacitor, optocoupler or other device. An isolator is typically used for either the low voltages and currents associated with signal transfers, or the much higher voltages and currents of line power. In some cases however, a single isolator may serve both purposes.

Equipment operating on line power may be subject to high-voltage surges and extreme transient spikes. Line voltage disruptions can occur when heavy equipment such as motors power on or change loads, with the electronic noise interfering with signals in the control circuitry, potentially causing operational problems. Besides entering the system from outside, noise may originate from within, so isolation must prevent noise feedback as well as its entry.

Other sources of environmental noise can include communications cables that result in unintended ground loops. Multiple internal voltage levels mean that some parts of the system can potentially interfere with other parts, and high-frequency transmitters and processors have to be prevented from corrupting low-frequency signals. Isolation serves to prevent these problems keeping the system running as intended.

Automated Equipment Requirements:

Factory automation, especially in intelligent sensors and programmable logic controllers (PLCs), demands robust performance from isolating elements, together with smaller size. Small-footprint sensors are increasingly incorporated in processes for temperature, moisture, vibration, chemical and other types of control. In these systems, low-current circuitry must isolate high-frequency microcontrollers and wireless transmission, as well as sensing elements that are subjected to external conditions.

PLCs regulate multiple units on the factory floor and are often networked to plant offices. These systems, operating with multiple voltage levels, continually demand rescaling to pack in more channels for greater operational control within the same space. In addition, new high-speed communications in PLC backplanes require reduced signal latency for greater bandwidth. Isolation permits functions in these complex systems to operate without mutual interference.

Technology Requirements

Rigorous tests for isolation devices specify maximum repetitive peak voltages, maximum transient and surge levels, and working voltage levels over time. Also important is Common Mode Transient Immunity (CMTI) – a measure of how well the isolator prevents rapid changes in current from rippling across the barrier. To guard against shorting, measurements are specified for external distances separating power pins, and for the ability of the package to withstand breakdown over time.

Isolation that provides sufficient protection for operation is referred to as basic or functional isolation, a measure that industrial standards double for safety. IC manufacturers are now working to introduce more effective reinforced isolation that meets these standards and saves space by providing the equivalent of two or more times the basic level. Reinforced isolation requires improvements in design and packaging, as well as a highly rated dielectric within the isolating component.

Integrated Capacitor-Based Isolation

The challenge today is to find more effective ways to rescale traditionally bulky isolating components and integrate them on a chip, while at the same time improving signal bandwidth and lowering latency. Miniaturizing components while improving their characterization is a difficult goal in itself, but integration also introduces into the IC package the same power and signal interferences that are meant to be kept away by the isolators.

Of the various components used as isolators, capacitors are the most straightforward to integrate. The technology for integrating capacitors on a silicon die is well understood, and the silicon dioxide (SiO₂) that provides on-chip insulating layers is an excellent dielectric. However, the speeds that are operative still require isolation between high- and low-frequency circuits that can be achieved only by using separate chips. The solution is an MCM, where high-frequency circuitry resides on one chip and lower-frequency circuitry on the other. Bond wires between the two devices connect to capacitive pads that isolate incoming signals before relaying them to internal circuitry.

Recently introduced IC solutions leverage this technology to provide capacitor-based reinforced isolation. Texas Instruments’ ISO78xx multichannel digital isolators, for instance, provide protection for up to 8000 volts at peak and transmission speeds up to 100 megabits per second. MCMs like these save space and provide reinforced isolation that meets industrial specifications.

Protecting people and machines and maintaining signal integrity are responsibilities of isolation. Today, this long-established technology is receiving renewed attention as factory automation demands more connection, communication and control to achieve new levels of precision and efficiency. Intelligent PLCs and sensors are driving the need for new forms of isolation, but the benefits will extend to all industrial equipment, as well as other markets. New MCM integrated solutions with reinforced capacitor-based isolation are already proving their value, and continued innovation is expected in the future.

 

[END]

 

 

[Ashutosh Bhatt]

whats this?

[Author]

Posts