Category Archives: IC’s

Improving Power Management Efficiency

Design engineering teams face considerable challenges handling conflicting requirements for portable types of medical devices. Most of these devices are always-on types and must be capable of managing battery life with maximum efficiency and effectiveness. They also must have suitable dimensions tailored to the patient’s comfort, especially as most of these are meant to be worn 24 hours a day. Therefore, not only must their construction be robust, but they must also deliver the highest levels of performance. Designers use PMICs or power management integrated circuits for optimizing the power utilized by the ultra-low architecture, improving the sensitivity of measurements, and keeping the SNR or signal-to-noise figures on the high side.

Wearable technology is benefitting from the growing popularity of mobile networks from the perspective of both, the healthcare and the consumers. Although their design was initially meant for sports and wellness, the medical market is now finding increasing use for wearables. As a consequence, newer generations of medical wearable devices are available using MEMS or micro-electromechanical system sensors, including heart-rate monitors, gyroscopes, and accelerometers. Other sensors are also in use, such as for determining skin conduction and pulse variability. However, the more sensitive the sensor, the more it faces SNR issues so designers need to use better noise reduction techniques along with more efficient energy-saving solutions.

For instance, the accuracy of optical instruments depends on many biological factors. Therefore, design engineers maximize the sensitivity of optical instruments by improving their SNR over a wide range. They use voltage regulator ICs with low quiescent currents along with elements that improve the SNR by reducing ripple and settling times.

Maxim offers a complete SCODAS or single-channel optical data acquisition system, the MAXM86161. They have designed its sensor module for use in in-ear and mobile applications. They have optimized it for SPO2 or oxygen saturation in the blood, HR or reflective heart rate, and continuous monitoring of HRV or heart rate variability. There are three high-current programmable LED drivers on the transmitter part of the MAXM86161. While the receiver part has a highly efficient PIN photo-diode along with an optical readout channel. It features a low-noise signal conditioning ALE or analog front end. It includes a 19-bit ADC or analog to digital converter, a high-performance ALC or ambient light cancellation circuit, and a picket fence type detect-and-replace algorithm.

Optimizing the energy efficiency of an optical measuring instrument is a constraint on its design. Rather than use regular LDO or low-drop-out regulators, designers now use novel switching configurations to improve the efficiency further. The requirement is that the voltage regulation element provides a low level of ripples at high frequencies so that there is no interference when measuring heart rates. To operate LEDs at voltages different from what the Li-ion batteries can supply, designers use new buck-boost converter technologies, thereby curbing energy consumption and saving board space. For instance, they use the SIMO or single-inductor multiple-output buck-boost architecture for reducing the number of inductors and ICs the circuit requires.

The MAXM86161 from Maxim Integrated is a PMIC or power-management integrated circuit and is meant for applications that are space-constrained and battery-powered, where the efficiency must be high within a small space.

SiC MOSFETs Enhance Performance and Efficiency

Power applications across industries demand smaller sizes, greater efficiency, and enhanced performance from the electronic equipment they use. These applications include energy storage systems, battery chargers, DC-DC and AC-DC inverters/converters, industrial motor drivers, and many more. In fact, the performance requirements have become so aggressive that they surpass the capabilities of silicon MOSFETs. Enter new transistor architectures based on silicon carbide or SiC.

Although silicon carbide devices do offer significantly enhanced benefits across most critical performance metrics, the first-generation SiC devices had various application uncertainties and limitations. The second-generation devices came with improved specifications. With pressures for time-to-market increasing, manufacturers improved the performance of SiC MOSFETs, and by the third generation of devices, there were vast improvements across key parameters.

While silicon-based MOSFETs significantly enhanced the design of power electronic equipment, the insulated-gate bipolar transistor or IGBT also helped. The IGBT is a functionally similar semiconductor, its construction is vastly different, and its switching attributes are more optimized. This led to power electronic equipment adopting switched topologies, thus becoming far more efficient and compact.

The main characteristics of switched mode topologies are based on some form of PWM or pulse-width modulation. They use a closed-loop feedback arrangement for maintaining the desired current, voltage, or power value. With the increasing use of silicon MOSFETs, the demand for better performance also increased. Regulatory mandates demanded new efficiency goals.

With a considerable effort in R&D, an alternative emerged. This was the SiC power-switching device, that used silicon carbide as the substrate rather than silicon. Deep-physics changes have allowed these SiC devices three major advantageous electrical characteristics over silicon-alone products. These characteristics offer operational advantages and subtle differences.

The first of these three main characteristics is a higher critical breakdown voltage. While silicon-based products offer 0.3 MV/cm, SiC-based products offer 2.8 MV/cm. This results in products with the same voltage rating now being available in a much thinner layer, effectively reducing the drain to source on-time resistance.

The second main characteristic is higher thermal conductivity. This allows SiC-based devices to handle much higher current densities in the same cross-sectional area, as compared to that silicon-based devices can.

The final characteristic is a wider bandgap. This is the difference in energy measured in electron volts between the bottom of the conduction band and the top of the valence band in many types of insulators and semiconductors. This results in a lower leakage current at higher temperatures. Because of the above reasons, the industry also refers to SiC devices as wide bandgap devices.

In general terms, SiC-based devices can handle voltages that are ten times higher than Si-only devices can. They can also switch about ten times faster, besides offering an on-time drain-to-source resistance of half or lower at 25 °C, even when using the same die area as a Si-only device. Moreover, the switching-related loss at turn-off periods for SiC devices is significantly lower than those for Si-based devices. Additionally, it is easier to handle thermal design and management issues with SiC-based devices, as they can operate at much higher temperatures, such as up to 200 °C, as compared to 125 °C for Si-based devices.

What is Capacitance to Digital Converter Technology?

The healthcare industry has witnessed many advancements, innovations, and improvements in electronic technology in recent years. Healthcare equipment faced challenges like developing new treatment methods and diagnoses, home healthcare, remote monitoring, enhancing flexibility, improving quality and reliability, and improving ease of use.

A comprehensive portfolio of these technologies includes digital signal processing, MEMS, mixed-signal, and linear technologies that have helped to make a difference in healthcare instrumentation in areas such as patient monitoring and imaging. Another is the capacitance to digital converter technology that offers the use of highly sensitive capacitance sensing in healthcare applications. For instance, a capacitive touch sensor is a novel user input method that can be in the form of a slider bar, a push button, a scroll wheel, or other similar forms.

In a typical touch sensor layout, a printed circuit board may have a geometric area representing a sensor electrode. This area forms one plate of a virtual capacitor, while the user’s finger forms the other plate. For this system to work, the user must essentially be grounded with respect to the sensor electrode.

Analog Devices has designed their CapTouch controller family of ICs, the AD7147/ AD7148, to activate and interface with capacitance touch sensors. The controller ICs measure capacitance changes from single-electrode sensors by generating excitation signals to charge the plate of the capacitor. When another object, like the user’s finger, approaches the sensor, it creates a virtual capacitance, with the user acting as the second plate of the capacitor. A CDC or capacitance to digital converter in the ICs measures the change in capacitance.

The CDC can measure changes in the capacitance of the external sensors and uses this information to activate a sensor. The AD7147 has 13 capacitance sensor inputs, while the AD7148 has eight. Both have on-chip calibration logic for compensating for measurement changes due to temperature and humidity variations in the ambient environment, thereby ensuring no false alarms from such changes.

Both CDCs offer many operational modes, very flexible control features, and user-programmable conversion sequences. With these features, the CDCs are highly suitable for touch sensors of high resolution, acting as scroll wheels or slider bars, requiring minimum software support. Likewise, no software support is necessary for implementing button-sensor applications with on-chip digital logic.

The CDCs function by applying an excitation signal to one plate of the virtual capacitor, while measuring the charge stored in it. They also make the digital result available to the external host. The CDCs can differentiate four types of capacitance sensors by changing the way they apply the excitation.

By varying the values of these parameters, and/or observing the variations in their values, the CDC technology directly measures the capacitance values. The distance between the two electrodes affects the output of the CDCs in inverse proportions.

The family of Analog Device CDCs, the AD714x, AD715x, and AD774x, are suitable for applications involving a wide range of functions. These involve various input sensor types, input ranges, resolutions, and sample rates. Applications involve liquid level monitoring, sweat detection, respiratory rate measurement, blood pressure measurement, and more.

Double-Sided Cooling for MOSFETs

Emission regulations for the automotive industry are increasingly tightening. To meet these demands, the industry is moving rapidly towards the electrification of vehicles. Primarily, they are making use of batteries and electric motors for the purpose. However, they also must use power electronics for controlling the performance of hybrid and electric vehicles.

In this context, European companies are leading the way with their innovative technologies. This is especially so in the development of power components and modules, and specifically in the compound semiconductor materials field.

ICs used for handling electrical power are now increasingly using gallium nitride (GaN) and silicon carbide (SiC). Most of these devices are wide-bandwidth devices, and work at high temperatures and voltages, but with the high efficiency that is typically demanded of them in automotive applications.

Silicon Carbide is particularly appealing to the automotive industry because of its physical properties. While silicon can withstand an electrical field of 0.3 MV/cm before it breaks down, SiC can withstand 2.8 MV/cm. Additionally, SiC offers an internal resistance 100 times lower than that of silicon. These parameters imply that a smaller chip of SiC can handle the same level of current while operating at a higher voltage level. This allows smaller systems if made of SiC.

Apart from functioning more efficiently at elevated temperatures, a full SiC MOSFET module can reduce switching losses by 64%, when operating at a chip temperature of 125 °C. Power control units for controlling traction motors in hybrid electric vehicles must operate from engine compartments, and this places additional thermal loads on them.

Manufacturers are now exploring various solutions for improving the efficiency, durability, and reliability of SiC MOSFETs under the above operating conditions. One of these is to reduce the amount of wire bonding by using double-sided cooling structures. This cools the power semiconductor chips more effectively. Therefore, overmolded modules with double side cooling are rapidly becoming more popular, especially for mid-power and low-cost applications.

As a result of the research at the North Carolina State University, researchers have developed a prototype inverter using SiC MOSFETs that can transfer 99% of the input energy to the motor. This is about 2% higher than silicon-based inverters under regular conditions.

While an electric vehicle could achieve only 4.1 kW/L in the year 2010, new SiC-based inverters can deliver about 12.1 kW/L of power. This is very close to the goal of 13.4 kW/L that the US Department of Energy has set for inverters to be achieved by 2020.

With the new power component using double-sided cooling, it is capable of dissipating more heat effectively in comparison to earlier versions. These double-sided air-cooled inverters can operate up to 35 kW, easily eliminating the need for heavy and bulky liquid cooling systems.

The power modules use FREEDM Power Chip on Bus MOSFET devices to reduce parasitic inductance. The integrated power interconnect structure helps achieve this. With the power chips attached directly to the busbar, their thermal performance improves further. Air, as dielectric fluid, provides the necessary electrical isolation, while the busbar also doubles as an integrated heatsink. Thermal resistance for the power module can reach about 0.5 °C/w.

TI Driver for BLDC Motors

When simple motors were more frequently used, it was relatively easy to design products with them. Controlling such motors was simple, whether it was a brushed DC motor or a single-phase AC motor. There was no need for sophisticated hardware or software for designing a product with a motor.

However, sophisticated BLDC or brush-less DC motors are replacing most of the above motors because of several advantages like quiet operation and high efficiency. But these advantages come at the cost of design knowledge and effort, requiring both hardware and software development. Texas Instruments has developed a new integrated circuit that allows designers to achieve all the benefits easily from these motors.

The biggest benefit offered by BLDC motors over older designs is their improved power efficiency. Most government regulators today demand that electrical products meet strict efficiency standards. In most cases, meeting these requirements is possible only through the use of BLDC motors.

Motors are mechanical devices and therefore, they make noise when operating. Although the quiet operation is not usually a design goal for most products, using a BLDC motor offers a way to achieve low noise operation.

There are further advantages to using BLDC motors. One of them is low voltage operation, and the other is a longer life. Manufacturers of BLDC motors are now offering them in larger sizes for use in bigger products.

As stated earlier, BLDC motors are now replacing brushed DC motors and in some cases, AC motors as well. Some practical examples are robotic vacuum cleaners, pumps, fans, washing machines, humidifiers, and air purifiers. They are useful for multiple automotive devices as well.

Functionally, a BLDC motor works under the same principles that govern the operation of all motors—rotation is from the interaction of two magnetic fields, one fixed and the other movable. Frequently, the BLDC motor will have multiple stator coils embedded in the periphery of the motor assembly. With the stator coil wired into three groups, it performs as a three-phase motor does. The rotor on the BLDC motor consists of several permanent magnets rotating in the circle formed by the stator coils. The user only has to apply a sequence of pulses to the stator coils.

The timing of the pulses must match their interaction with the permanent magnets. The control circuitry that drives the stator coils gets the correct timing from multiple sensors indicating the orientation of the rotor. These sensors are mostly Hall-effect devices that produce signals that the controller requires for moving the magnetic fields on the stator coil.

There are numerous variations of the approach to control the BLDC motor. One of them is a sensor-less method using the back electromotive force the rotating rotor magnets induce into the stator coils. The sensor-less method typically reads the feedback voltages in the motor stator winding and processes them into control signals.

Many motor controllers are pre-programmed and packaged BLDC motor control modules. This is usually satisfactory for common applications. Others, however, require a custom design. The MCF8316A from TI is a single chip BLDC motor controller chip that only requires inputs for speed, direction, and torque. The IC takes care of the rest.

Low-Power Circuit Timing using SPXOs

A wide range of electronic devices relies on circuit timing as a critical function. These include microcontrollers, Bluetooth, Ethernet, Wi-Fi, USB, and other interfaces. In addition, circuit timing is essential for consumer electronics, wearables, the Internet of Things (IoT), industrial control and automation, test and measuring equipment, medical devices, computing devices and peripherals, and more. Although designing crystal-controlled oscillators seems an easy process for providing system timing, there are numerous design requirements and parameters that designers must consider when matching a quartz crystal to an oscillator chip.

Among the several considerations are the negative resistance of the oscillator, its drive level, resonant mode, and the motional impedance of the crystal. When the designer is making the circuit layout, they must consider the parasitic capacitance of the PC board. They must also consider the on-chip integrated capacitance, and include a guard band around the crystal. Finally, the design must not only be compact, with a minimum number of components, and reliable. While the circuit must be capable of operating with a wide range of input voltages, consuming minimal power, it must also have a small root-mean-square jitter.

An optimal solution to the above is to use simply packaged crystal oscillators or SPXOs. Manufacturers optimize SPXOs for low RMS jitter and minimal power consumption. These devices can operate with any supply voltage ranging from 1.6 VDC to 3.6 VDC. With these continuous-voltage oscillators, designers can implement solutions requiring minimal effort while integrating them into digital systems.

In small, battery-powered, wireless devices, power consumption is always a very important consideration. That is why designers prefer to base such devices on the system on a chip or SoC processor that consumes very low power to support battery lives of several years. Moreover, device cost depends on the battery size, as the battery is easily the most expensive component in the device—minimizing the battery size is, therefore, an important factor in small wireless devices. For battery life consideration, one of the important parameters is the standby current, apart from the self-discharge current of the battery. Minimizing the current drawn by the clock oscillator is important, as this is greater than the standby current.

Designing low-power oscillators can be challenging. Designers are tempted to save energy by allowing the circuit to enter a disabled state for minimizing the standby current while starting the oscillator when needed. However, this is not an easy task as starting crystal oscillators quickly is not a simple and reliable task. Reliable start-up conditions require careful design efforts when designers attempt it across all environmental and operating conditions.

Most low-power wireless SoCs favor the Pierce oscillator configuration. The circuit has crystal and tow load capacitors. It uses an inverting amplifier that has an internal feedback resistor. With the amplifier feeding back its output to its input, the right conditions cause a negative resistance to start the oscillations going.

Quartz crystal oscillators can have jitters caused by power supply noise, improper load, improper termination conditions, the presence of integer harmonics of the signal frequency, circuit configurations, and amplifier noise. The designer must use several methods to minimize jitter.

Small LED Driver IC

Although Switch-mode and PWM or Pulse Width Modulation methods make very efficient drivers for LEDs, they are also a good source of electromagnetic noise. Many applications require low noise conditions for proper operations, especially those related to medical. These low-noise applications benefit from linear circuits that introduce far lower noise in the system as compared to the Switch-mode or PWM topologies.

For driving LEDs linearly, Infineon Technologies AG offers a small LED driver IC, the BCR431U. Available in a tiny SMT package SOT23-6, the BCR431U can regulate the operating current to the LED in a standalone operation without requiring the help of an external power transistor.

Operating between a voltage range of 6 to 42 VDC, the BCR431U can drive LED currents up to 37 mA. A high-value resistor connected between the pins Rset and RS of the IC allows setting the desired LED current level.

The major advantage of the BCR431U LED driver is its low-drop feature. At a full load of 37 mA, the IC drops only 200 mVDC across from the supply to the output. At 15 mA load, this voltage drop is only 105 mVDC. This feature has two benefits—one, the power dissipation in the driver IC at full load is only 7.4 mW, and two, the user can drive a string of LEDs in series connection mode by adjusting the input voltage. Over the entire current range, the driver IC maintains precision of ±10% of the set value of the LED current.

The low voltage drop across the BCR431U LED driver improves the system efficiency substantially while allowing extra voltage headroom to compensate for the tolerances of forward voltages of LEDs. Therefore, even if some LEDs in the string have different forward voltages, the driver IC can accommodate them with an increase or decrease in the driving voltage. Likewise, it can accommodate tolerances in supply voltage sources when used in multiple applications.

Internal circuit configurations ensure the BCR431U LED driver IC can keep the LED current under control, even when the temperature changes. If the junction temperature of the driver IC rises, a temperature controlling circuit within the IC reduces the LED current, thereby helping to bring down the junction temperature. Therefore, the BCR431U can protect itself from thermal runaway.

The linear low-drop LED current driver IC BCR431U is eminently suitable for driving long strips of low-power and low-voltage LEDs. Highly flexible in adjusting to 12, 24, or 36 VDC power supplies, the driver IC offers high precision and efficiency when driving LEDs. Internal thermal protection built into the driver IC ensures long-life operations, preventing accidental damages and protections against surge events. Infineon has designed the IC BCR431U to be robust enough to withstand high ESD conditions.

Applications for BCR431U are almost endless including driving LED strips, LED channel letters and displays, architectural LED lights and displays, emergency lights, retail lights for decoration, shop window LED lights, and many more. The driver IC is especially helpful in shops for driving LED lights in shops showcasing items in different colors.

High-Speed Ceramic Digital Isolator

Isolated systems can communicate digitally among themselves without conducting ground loops or presenting hazardous voltages—simply by using digital isolators. A capacitive isolation barrier exists between the isolated systems. The transmitter side modulates its digital data with a high-frequency signal that allows it to transmit across the capacitive isolation. Receivers on the other side detect the signal, demodulate it to extract the digital data, and use it.

Digital isolators offer thick insulation distances of greater than 0.5 mm, with reliable high-voltage insulation. ON Semiconductor has patented an off-chip galvanic capacitor isolation technology and offer a full-duplex, high-speed, bi-directional, dual-channel digital isolator—the NCID9211.

NCID9211 supports isolated communications. Therefore, isolated systems do not need conducting ground loops to communicate with digital signals, and it is possible for them to avoid hazardous voltages. The optimized IC design and the off-chip galvanic capacitor isolation technology that ON Semiconductors has developed ensures high noise immunity and high insulation. The power supply rejection and common-mode rejection ratio specifications of the NCID9211 support this. Compared to coreless transformers and thin-film on-chip capacitors, the thick film substrates offer capacitors with 25 times the dielectric thickness.

The digital isolator offers a unique combination of an insulating barrier and an electrical performance along with safety and reliability that only optocouplers had offered so far. NCID9211 comes in a 16-pin small outline package with a wide body. The device has features with several advantages.

NCID9211 is the only digital isolator in the market today that includes insulation reliability matching that offered by optocouplers while offering the same level of safety. The device has a distance through insulation or DTI or over 0.5 mm and uses off-chip capacitive isolation for achieving maximum high-voltage insulation reaching 2000 Vpeak.

The off-chip capacitive isolation offers better long-term reliability and safety compared to other digital isolation methodologies available in the market. ON Semiconductors guarantees the specifications of the NCID9211 over a supply voltage range of 2.5-5.5 DVC and an extended temperature range of -40 °C to +125 °C. The device does not require overdesign as the device performance remains stable over voltage and temperature.

NCID9211 offers a high-speed communication of NRZ or non-return to zero data at rates of 50 Mbits per second. The maximum propagation delay is only 25 ns, while the maximum distortion of the pulse width is only 10 ns.

ON Semiconductor claims NCID9211 has better performance over optocouplers. Compared to optocouplers, NCID9211 does not exhibit insulation material wear out over time up to 1500 V, there is no LED to degrade over time, and the performance across devices is more consistent. Compared to optocouplers, NCID9211 has a longer lifetime expectancy.

With a minimum common-mode rejection of 100 KV/µs, the NCID9211 has a superior noise immunity and it meets stringent performance requirements of EMI/EMC. However, for meeting reliable high-voltage insulation requirements, there must be a minimum creepage and clearance distance of 8 mm between the input and the output.

With full-duplex and bi-directional communication, the NCID9211 has several applications such as isolated PWM control, SPI and I2C type micro-controller interfaces, voltage level translators, isolated data acquisition systems, and many more.

Using Integrated Power Switches

Power switches are most commonly in demand for their simplicity in turning on and off a voltage rail or for protecting a power path. Engineers find load switches easier to use compared to discrete power MOSFETs. For complete power protection of the system, eFuses offer an integrated approach. The combination of load switches and eFuses offers more than significant PCB space savings. Compared to discrete circuits, the combination of load switches and eFuses, also known as integrated switches, offers substantial improvements in performance, while resolving common power management challenges such as faster current limiting, detecting, and responding to mistakes in field wirings, and improving battery life and power density.

In fact, using the right integrated switch helps to reduce EMI and heat generation, while improving the power efficiencies to 90%. Bad power management leads to several side effects such as the generation of excess heat, electromagnetic interference, inaccurate voltage control, and these can lead not only to poor device performance but even to its outright failure. For the above reasons, designers are using integrated switches in electronic equipment such as desktop computers, LCD TVs, and plasma TVs.

Using integrated power switches offers several advantages over solutions of discrete controller and MOSFET. The loser component count leads to lower cost and higher reliability.

With electronic products shrinking in size, PCB space is almost always at a premium. The integrated power switch with its lower footprint has a better advantage over discrete components. Several manufacturers offer a variety of integrated power switches, and these include Fairchild Semiconductors, Power Integrations, ON Semiconductors, and ST.

Fairchild Semiconductor offers their new Green FPS e-Series of integrated switches as a replacement for conventional, flyback converters using hard switches. The new e-Series are a versatile set of devices for improving efficiency by reducing switching losses in the MOSFET with quasi-resonant operation.

It is also possible to use the e-Series in the continuous conduction mode or CCM in fixed frequency operations. The design offers simplicity and lowers the ripple current. Using an advanced burst mode technique, devices of the e-Series also conform to several governmental agency requirements for standby efficiency.

Fairchild uses a prefix of FSQ in the part number of these devices, and they are available for applications that can deliver up to 90 W. Depending on the requirement, it is possible to avail the series in seven different packages including DIP, TO-220F, LSOP, and others.

The devices use valley switching along with inherent frequency modulation for the quasi-resonant operation. The improves efficiency while reducing the EMI signature of the power supply. Valley switching uses the natural resonance of the primary inductance of the transformer and both circuit capacitance and parasitic capacitance for turning the MOSFET on only when the drain-to-source voltage is at its minimum. This reduces the amplitude of the current spike at turn-on typically found in hard-switched converters.

The increased efficiency from reducing the turn-on current spike also reduces the stress on the MOSFET.  However, with valley switching, the power supply can operate with a variable switching frequency, changing with changes in the line and load conditions, helping to reduce the EMI the power supply generates.

Isolated RS-485 Transceivers

A standard RS-485 transceiver sends and receives digital signals between digital equipment. They use positive and negative signals limited to 5 VDC levels. One can connect them as simple point-to-point configuration or as multi-point connections with two or more devices communicating. RS-485 transceivers allow high-speed communication in electrically noisy environments, as is usual within industrial plants.

Each of the two output lines on an RS-485 transceiver uses square waves to send serial data to another distant transceiver. A capacitive line offers high impedance to high-speed transmission, distorting the rise and fall of the signals. A capacitive line is one where the line carrying the signals is close to the signal ground.

Rather than use capacitive lines, RS-485 transceivers use a balanced line where the two output lines carry voltages of opposite polarity all the time. In balanced lines, the signal rise and fall times are much better, resulting in transmitting high-speed signals over longer distances.

Using +5 VDC and -5 VDC for each of the two output lines alternately an RS-485 transceiver can offer either non-inverting or inverting signals on its output lines. When the output is non-inverting, its polarity is the same as that at the input of the transceiver. For the inverting pin, the polarity is always opposite to that at the input.

In an industrial application, using isolated RS-485 transceivers is the normal practice, as the interconnecting cable often must pass through an environment with high voltages present. The isolation prevents any high-voltage spike inadvertently appearing on the interconnecting cable and passing on to the circuit driving the transceivers.

Analog Devices offers two types of isolate RS-485 transceivers. The ADM2867E is signal and power isolated up to 5.7 kV rms, while the ADM2561E has isolation levels up to 3 kV rms.

Both transceivers pass radiated emission testing, conforming to the requirements of EN55032 Class B standard. The tests use a double-layer PCB with two small 0402 size external ferrite beads on isolated ground and power pins.

Both devices feature integrated but isolated DC-DC converters generating low EMI. The isolation barrier offers immunity to system-level EMC standards. On the A, B, Y, and Z pins of the RS-485, a family of isolator devices offer ±15 kV air and ±12 kV contact ESD protection complying with the IEC6100-4-2 standard. Cable invert pins on the device allow users to reverse cable connections to quickly correct the connection while maintaining fail-safe performance on the receivers.

A double-layered PCB reduces the design time and material costs while providing Class B radiated Emissions. The cable invert feature reduces debug time during system install by allowing users to easily correct installation errors. With a greater than 8 mm creepage and clearance, and the IEC 6100-4-2 ESD and 5.7 kV digital isolation, the RS-485 transceivers from Analog Devices can maintain signal integrity even when the signals are passing through the harshest of environments.

Isolated RS-485 transceivers are useful for industrial automation, communication, building and infrastructure, and in aerospace and defense, mainly because of their cable invert feature, high isolation, low EMI/EMC capabilities, good surge protection, and improved ESD safeguards.