Recently, it was brought to my attention that Silicon Labs’ Isolators were part of a study at Aalto University in Finland. The study was conducted by Mikael Lumio as part of his Master’s program. The results are interesting and one of the most comprehensive, independent studies of isolation performance I have seen.
The full thesis is available here.
Mr. Lumio approaches some of the concerns surrounding CMOS-based isolation straight on. In his thesis, he compares different types of CMOS isolation against each other and against the legacy optocoupler solutions. Capacitive-based isolators (the preferred technology from Silicon Labs), inductive (transformer)-based isolators, and magnetoresistive-based isolators are all included in the analysis. For many specs, the capacitive-based solutions outperform other technologies. Compared to optocouplers, Mr. Lumio’s analysis clearly shows advantages of CMOS-based isolation in common-mode transient immunity (CMTI), current consumption per channel, data rate, skew, and other timing specifications.
In addition to comparing datasheet specifications, Mr. Lumio also compares isolation performance. Mr. Lumio’s thesis does an excellent job of describing the different isolation parameters that are commonly specified by international certifying agencies. Then, the thesis uses those descriptions to aide in the comparison of different CMOS isolation technologies. For all technologies, the isolation capability is on par with legacy optocoupler devices. The only lagging parameter is in surge immunity, but CMOS-based isolators are catching up fast.
Mr. Lumio’s thesis is particularly focused on the application of isolation technology to variable frequency drive (VFD) systems. VFDs are increasingly used in all types of motor drive applications. Motor drive efficiency standards worldwide encourages the use of variable frequency drives wherever it is applicable to a motion application. The thesis lists, “blowers, compressors, conveyor belts, cooling and recirculating pumps, cranes, factory robotics, fans, elevators, hoists, mixers, paper mills, and printing presses,” as relevant applications where VFDs are prescribed for efficiency improvement.
VFDs are usually powered from rectified AC line inputs and are used to provide a three-phase, AC output to a motor. The supply provides a high DC voltage for the rest of the system. Isolation is necessary in several parts of the typical system. The VFD is converting the DC supply into an AC signal through a multi-phase inverter stage. The inverter has switches connected to the high voltage power rail and isolation must be utilized to protect the control circuit. The output of the drive is connected to the windings of the motor. Often each winding has an isolated sensor connected for current and voltage measurement. Both safety isolation, for protection of operators and people interfacing with the system, and functional isolation, for circuit protection, are necessary in the system.
Besides specific isolation requirements, Mr. Lumio looked at additional features of CMOS-based isolation to evaluate its suitability for use in VFDs. Electromagnetic compatibility (EMC) was of particular concern. ESD performance was also evaluated. Finally, the relative cost of the various CMOS isolators was considered.
On the subject of cost, the thesis found that at mass production volumes CMOS-based isolators are less expensive. In his analysis, Mr. Lumio included not only the device cost but also indirect costs including the reduction in PCB area and component count. For the typical fieldbus serial communication application, Mr. Lumio’s research indicates a close to 1/5 cost reduction in moving from a legacy optocoupler solution to a modern isolation solution. For a more specific IGBT drive function, the cost reduction wasn’t as large. It was still significant, though, at approximately 1/10.
EMC was a focus for Mr. Lumio’s thesis because of the environments in which VFDs operate. High voltage switching associated with motor drive means that the components used must be immune to a large amount of electromagnetic noise. Mr. Lumio found that modern CMOS-based isolators performed as expected even in the presence of large amounts of electromagnetic interference. Silicon Labs’ isolators showed great robustness in all test. For example, in the RF immunity evaluation, Silicon Labs’ isolator was free of errors even in the presence of 20 V/m RF energy.
In his own words, Mr. Lumio writes, “Digital isolators from Silicon Laboratories were in the top group of manufacturers in all of the tests.” His thesis is additional evidence for the suitability of CMOS isolators in demanding applications that require high reliability, like motor drives. We’re proud that Silicon Labs’ capacitive based isolation fared well in all of Mr. Lumio’s analysis and it’s our goal to deliver higher performance, more reliable isolated circuits than competing solutions. For more information, visit our Isolations Solutions page.
Fossil-fueled electric power facilities have proven to be robust and reliable sources of energy for more than a century, but these tried-and-true facilities are large, complex and increasingly expensive to build. It's also challenging and costly to operate them cleanly with a minimal carbon footprint and environmental impact.
Photovoltaic (PV) power systems consist of multiple components, such as panels that convert sunlight into electricity modules, mechanical and electrical connections and mountings, and solar power inverters, which are essential for conveying solar-generated electricity to the grid.
What is a PV Solar Inverter?
PV panels convert sunlight into dc voltage, which must be converted to high-voltage ac to minimize line losses and enable longer power transmission distances. The PV solar inverter performs this dc-to-ac conversion and is the most critical component in any PV power generating system. However, this is just one key function that the PV inverter provides.
The PV inverter also offers a grid disconnect capability to prevent the PV system from powering a disconnected utility; that is, an inverter remaining on-line during grid disconnect or delivering power through an unreliable connection can cause the PV system to back-feed local utility transformers, creating thousands of volts at the utility pole and endangering utility workers. Safety standard specifications IEEE 1547 and UL 1741 state that all grid-tied inverters must disconnect when ac line voltage or frequency is not within specified limits or shut down if the grid is no longer present. Upon reconnect, the inverter cannot deliver power until the inverter detects rated utility voltage and frequency over a five minute period. But again, this is not the end of the inverter’s duties.
The inverter also compensates for environmental conditions that affect power output. For example, PV panel output voltage and current are highly susceptible to variations in temperature and light intensity per cell unit area (referred to as “irradiance”). The cell output voltage is inversely proportional to cell temperature, and cell current is directly proportional to irradiance. The wide variation of these and other key parameters causes the optimum inverter voltage/current operating point to move about significantly. The inverter addresses this issue by using closed-loop control to maintain operation at the so-called maximum power point (MPP), where the product of voltage and current is at its highest value.
In addition to these tasks, the inverter also supports manual and automatic input/output disconnect for service operations, EMI/RFI conducted and radiated suppression, ground fault interruption, PC-compatible communication interfaces and more. Encased in a ruggedized package, the inverter is capable of remaining in full-power outdoor operation for more than 25 years. No small feat.
Taking a Closer Look
The single-phase PV inverter example shown below uses a digital power controller and a pair of high-side/low-side gate drivers to drive a pulse-width modulated (PWM) full-bridge converter. Full bridge topology is typically used in inverter applications because it has the highest power carrying capability of any switch mode topology. Referring to the image below, the PWM voltage switching action synthesizes a discrete (albeit noisy) 60 Hz current waveform at the full bridge output. The high-frequency noise components are inductively filtered and produce the moderately low amplitude 60 Hz sine-wave. The filtered waveform is then passed through an output transformer that performs three functions: First, it further smoothes the ac waveform; second, it corrects the voltage amplitude to meet specified grid requirements, and third, it galvanically isolates the inverter’s dc input from the high-voltage ac grid.
PV inverter design is filled with design compromises that can cause designers much grief if the wrong trade-offs are made. For example, PV systems are expected to operate reliably and at full rated output for a minimum of 25 years, and yet they need to be competitively priced, forcing the designer to make tough cost/reliability trade-offs. PV systems need highly-efficient inverters because higher efficiency inverters run cooler and last longer than their less efficient counterparts, and they generate cash savings for both the PV system manufacturer and user.
The never-ending quest for high inverter efficiency creates more design trade-offs that can impact component selection (primarily gate drivers, power switches and magnetic components, such as transformers), PCB construction and inverter package thermal requirements. The PV panel’s output voltage also wanders badly as the exposure to sunlight changes; so, it is beneficial for the inverter’s input voltage range to match that of the PV panel’s output. This creates yet more design trade-offs that further impact system complexity, cost and efficiency, and this is just the hardware. Now let’s have a look at the control side of the problem.
The “brains” behind the inverter is its controller, usually a digital power controller (DPC) or digital signal processor (DSP). Typically, the controller’s firmware is implemented in a state machine format for the most efficient execution using non-blocking (fall-through) code, which prevents execution from inadvertently entering an endless loop. Firmware execution is hierarchal, typically servicing the highest priority functions more frequently than lower order functions. In the PV inverter case, isolated feedback loop compensation and power switch modulation are usually the highest priorities, followed by critical protection functions to support UL 1741 and IEEE 1547 safety standards, and finally followed by efficiency control (MPP). The remaining firmware tasks pertain mostly to optimizing operation at the present operating point, monitoring system operation and supporting system communication.
The PV inverter’s exposure to blazing heat and/or freezing cold temperatures for 25 years causes one to take pause when considering the components used in the inverter. Clearly, components, such as electrolytic capacitors that filter out ripple and optocouplers that provide galvanic isolation, have no chance of “going the distance.” Electrolytic capacitors dry out and die, and the optocoupler’s LED brightness gradually fades to a dim glow, halting operation. Workarounds for these delicate components consist of replacing electrolytic capacitors with high-value film capacitors (higher reliability but obviously higher cost).The optimal long-term solution is to dismiss the optocoupler in favor of modern CMOS isolation components.
CMOS process technology offers the advantages of high reliability, cost effectiveness, high-speed operation, small feature size, low operating power and operating stability over voltage and temperature extremes as well as many other desirable attributes. Moreover, unlike the Gallium Arsenide (GaAs) process technology used in optocouplers, devices fabricated in CMOS have no intrinsic wear-out mechanisms. The underlying CMOS isolation cell is capacitive, fully differential and highly-optimized for tight timing performance, low-power operation, and high immunity to data errors caused by external fields and fast common-mode transients. In fact, the advantages brought by CMOS process technology combined with proprietary silicon product design are making possible robust, “near ideal” isolation devices for the first time. These devices offer greater across-the-board functional integration, substantially higher reliability (60+ year isolation barrier lifetime), 40°C to +125°C continuous operation at maximum VDD, and substantial improvements in performance, power consumption, board space savings and ease-of-use.
21st Century Component Solutions for PV Inverters
PV inverter architecture does not end with the single-phase, transformer-based inverter shown in above. Other common types include high-frequency, bipolar, 3-phase, transformerless and battery-powered inverters. While these topologies differ from one another, they often share the need for the same component solutions. The block diagram below shows several CMOS isolation devices used in a transformer-based, three-phase inverter.
This is a classic closed loop architecture in which the digital controller modulates the power switch duty cycle to force the PV system output voltage amplitude and phase to exactly match that of the grid. These isolated gate drivers integrate safety-certified galvanic isolation (rated at 1 kV, 2.5 kV or 5 kV) and high-side level shifting functions in a single package, eliminating the need for external isolation devices. Each driver output is isolated from the next, enabling a mix of negative and positive voltage rail voltages to be used without latch-up.
Current feedback to the controller is provided by a single 4 mm x 4 mm x 1 mm CMOS isolated ac current sensor (its 1 kV isolation rating is limited by package size – larger packaged versions are rated up to 5 kVrms). These monolithic sensors have a wider temperature range, higher accuracy and higher reliability compared to current sense transformers. The sensor is reset on a cycle-by-cycle basis using the inverter gate control signals generated by the digital controller, eliminating the need for external reset circuitry. The grid feedback is a critical part of the system feedback control mechanism. A resistive attenuator is used to reduce the grid voltage to a range that is compatible with the PWM modulator, which converts the sine wave input to a discrete PWM waveform, and is safety isolated by the CMOS digital isolator.
PV systems are relative newcomers to the energy production field. Like other emerging technologies, PV systems will be subject to rapid changes as the technology matures. As a result, PV systems will undoubtedly continue to evolve to meet market demands for higher capacity, lower cost and higher reliability. As this happens, PV inverters will expand in functionality, and designers will demand more integrated, application-specific, component-level devices to further leverage and drive innovation in CMOS isolation. As these events unfold, PV power systems will become more widespread and ultimately represent a viable segment of the utility mainstream that significantly reduces our dependence on fossil fuels.
Learn more about our solutions for solar inverters here.
Green standards are challenging power designers to deliver more energy-efficient, cost-effective, smaller, and more reliable power delivery systems. A critical building block within ac-dc and isolated dc-dc power supplies is the isolated gate driver. These trends push the need for greater power efficiency and increased isolation-device integration.
Optocoupler-based solutions and gate-drive transformers have been the mainstay for switch-mode power supply (SMPS) systems for many years, but fully integrated isolated gate driver products based on RF technology and mainstream CMOS provide more reliable, smaller, and power-efficient solutions.
Anatomy of an Isolated Power Converter
Isolated power converters require power stage and signal isolation to comply with safety standards. The example below shows a typical ac-dc converter for 500 W to 5 kW power systems, such as those used in high- efficiency data center power supplies.
From a high-level perspective, this two-stage system has a power factor correction (PFC) circuit that forces power system ac line current draw to be sinusoidal and in-phase with the ac line voltage; thus, it appears to the line as a purely resistive load for greater input power efficiency.
The high-side switch driver inputs above are referenced to the primary-side ground, and its outputs are referenced to the high-side MOSFET source pins. The high-side drivers must be able to withstand the 400 VDC common-mode voltage present at the source pin during high-side drive, a need traditionally served by high- voltage drivers (HVIC).
The corresponding low-side drivers operate from a low voltage supply (e.g., 18 V) and are referenced to the primary-side ground. The two ac current sensors in the low-side legs of the bridge monitor the current in each leg to facilitate flux balancing when voltage mode control is used. The isolation barrier is provided to ensure that there is no current flow between the primary- and secondary-side grounds; consequently, the drivers for synchronous MOSFETs Q5 and Q6 must be isolated.
The secondary-side feedback path must also be isolated for the same reason.
Gate Driver Solutions
Although optocouplers are commonly used for feedback isolation, their propagation delay performance is not fast enough to achieve the full benefit of the synchronous MOSFET gate-drive isolation circuit.
Optocouplers with faster delay-time specifications are available, but they tend to be expensive while still exhibiting some of the same performance and reliability issues found in lower-cost optocouplers. This includes unstable operating characteristics over temperature, device aging, and marginal common mode transient current (CMTI) resulting from a single-ended architecture with high internal coupling capacitance. In addition, Gallium Arsenide- based process technologies common in optocouplers create an intrinsic wear-out mechanism (“Light Output” or LOP) that causes the LED to lose brightness over time.
Gate Drive Transformers
Given the above considerations, gate drive transformers have become a more popular method of providing isolated gate drive. Gate drive transformers are miniature toroidal transformers that are preferred over optocouplers because of their shorter delay times. They are faster than optocouplers, but cannot propagate a dc level or low-frequency ac signal. They can pass only a finite voltage-time product across the isolation boundary, thereby restricting ON time (tON) and duty cycle ranges.
These transformers must also be reset after each ON cycle to prevent core saturation, necessitating external circuitry. Finally, transformer-based designs are inefficient, have high EMI, and occupy excessive board space.
CMOS-based Isolated Gate Drivers
Fortunately, better alternatives to gate drive transformers and optocouplers are now available. Advancements in CMOS-based isolation technology have enabled isolated gate drive solutions that offer exceptional performance, power efficiency, integration, and reliability. Isolated gate drivers, such as Silicon Labs’ Si823x ISOdriver family, combine isolation technology with gate driver circuits, providing integrated, low-latency isolated driver solutions for MOSFET and insulated-gate bipolar transistor (IGBT) applications.
The Si823x ISOdriver products are available in three basic configurations (see Figure 2), including:
The Si823x ISOdriver family supports 0.5 A and 4.0 A peak output drive options and is available in 1 kV, 2.5 kV, and 5 kV isolation ratings. The high-side/low-side versions have built-in overlap protection and an adjustable dead time generator (dual ISOdriver versions contain no overlap protection or dead time generator). As such, the dual ISOdriver can be used as a dual low-side, dual high-side or high-side/low-side isolated driver.
These devices have a three-die architecture that causes each drive channel to be isolated from the others as well as from the input side. This allows the polarity of the high-side and low-side channel to reverse without latch-up or other damage.
Read the Whitepaper
To learn more about how isolated gate drivers can significantly increase the efficiency, performance, and reliability of switch-mode power supplies compared to legacy solutions, check out this whitepaper.
We just released the Si838x Isolator Family, the industry’s first high-speed, multi-channel PLC input isolators. We built them to meet the special demands of programmable logic controller (PLC) applications so they’re a compact, multi-channel, high-speed digital isolation solution for designers.
We wanted to address the many headaches designers face with PLC applications, such as high-noise environments causing optos to glitch and traditional solutions using optos that are high power, unstable, and low immunity. The Si838x Isolator Family addresses these concerns and more with an exciting new combination of high-speed channels, exceptional channel integration, bipolar input flexibility, high noise immunity, and 2.5k VRMS safety isolation previously unavailable.
Purpose-built solution for many PLC applications, the Si838x family is ideal for industrial I/O modules, computer numerical control (CNC) machines, and servo motor control as well as process automation controllers (PACs) used in distributed process control systems.
And PLC developers can now easily migrate their optocoupler-based designs to state-of-the-art digital isolation technology and take advantage of higher performance, greater design flexibility, higher channel density, and long-term reliability due to an incredible list of features:
Si838x PLC Field Input Isolator Family Highlights
To give designers a taste of the technology, we offer the Si838xISO-KIT evaluation kit for experimentation that includes:
Learn more here.
About eight years ago while attending NAB Show, the massive industry event hosted by the National Association of Broadcasters, I noticed a considerable amount of floor space dedicated to showing off the latest camera-equipped drones. Marketed then as a more cost-effective way for cinematographers to capture aerial footage, these quadcopters were still priced significantly out of reach for casual users.
But like any new technology, as it developed it became more accessible. Over the last few years in particular, drones have gained popularity in large part because of the quality of the cameras they are being outfitted with and the lengths manufacturers are going to in order to make them easier to fly (I bought a mini quadcopter last winter and promptly flew it into a tree).
This week Xiaomi announced its Mi Drone, an exciting development for potential drone customers given the company’s reputation for balancing sophisticated design and affordability.
Two important design considerations when developing unmanned aerial vehicles (UAVs) are precise motor control and small form factor and Xiaomi is using our C8051 F85x 8-bit microcontroller, joining a growing number of drone manufacturers that like its combination of fast PWM modulation and small footprint.
In addition to the highly-integrated, AEC-Q100 qualified MCUs, we offer a reference design that has everything you need to start a motor spinning in five minutes or less.
The C8051F850 Motor Control Reference Design includes a 12-bit ADC, precision internal reference voltage, two with programmable hysteresis, and built-in hardware shutdown capability independent PWM channels.
The C8051F850 Motor Control Reference Design includes:
We also have a Development Kit for the C8051 F85x family that provides everything needed to evaluate hardware and develop code, including a C8051F850 MCU board, wall-mounted power supply, USB cable and quick-start guide.
Today we announced an expansion to our EFM8 Busy Bee 8-Bit MCUs, our cost-effective and high-performance MCUs for embedded applications. When performance in demanding environments matters, the new EFM8BB3 devices deliver. And they do it in a package as small as 3x3 mm2without compromising performance.
The BB3 family includes new industrial grade (I-grade) devices as well as more memory (64 kB) and additional peripherals including four DACs, four configurable logic units, higher speed ADC, and higher pin count options. An extended temperature range of -40 to +125 °C (ambient) expands the utility of these devices into industrial applications including motor control, lighting, and others.
The BB3 MCUs includes configurable logic module that can be used for a variety of digital functions, such as replacing system glue logic, aiding in the generation of special waveforms, or synchronizing system event triggers. Since the function of the logic is completely programmable, it reduces the challenge of interfacing other chips in the system. It also reduces the cost and board space required for glue logics. This reduces the PCB space and also allows for faster time-to-market.
For applications operating at a wide temperature range, maintaining high performance throughout is important. This eliminates the need for external thermistors to measure temperature and adjust analog trimming coefficient accordingly. There’s also no need for costly and time consuming calibration and trimming based on operating temperature.
As modern designs require smaller packages and wider temperature ranges, the EFM8BB I-grade MCUs offers 2-64 kbyte flash, 0.5-4 kbyte RAM, along with high-resolution 12-bit ADC, high-speed 12-bit DACs, low power comparators, voltage reference, enhanced throughput communication peripherals, and internal oscillators in packages as small as 3x3 mm2. This saves both cost and board space for applications that needs to operate at wide temperature range.
Today we announced our Si534xH clock family, a high-frequency, flexible clocking solution designed to cut cost and complexity for system-level development. The Si5344H and Si5342H clocks will replace current timing tools that rely on large, expensive voltage-controlled VCSOs that only support single, fixed frequencies. This frequency flexibility is coupled with jitter performance of 50 fs RMS.
The ability for service providers to send more data over existing fiber while minimizing the need for network upgrades is made possible by coherent optics, and this new offering simplifies things by integrating more functions into a smaller footprint.
Other features include:
The Si5344H-EVB and Si5342H-EVB evaluation boards, priced at $199 each (USD MSRP), are available to simplify device evaluation and system-level timing design. To order clock samples and evaluation boards, visit www.silabs.com/timing.
Today, we released the Si5121x Tiny Clock family with ClockBuilder Pro, the industry’s smallest programmable LVCMOS clock generators. Ideally suited for designers requiring multiple crystals and oscillators up to 170MHz on a single board, the Si5121x family replaces up to three of these components to simplify design and save board space.
Additionally, the new family is supported by ClockBuilder Pro (CBPro), which has been specifically designed to simplify clock tree and device configuration. With CBPro, you can create a frequency plan, get a custom part number, or program a device into an evaluation board.
Other Benefits include:
Check out our Si5121x evaluation kits here.
In case you missed it, last week we launched a family of isolated gate drivers specifically for power supply designs. The new Si827x ISOdriver family builds on our reputation in digital isolation and offers the highest noise immunity on the market.
Power per volume is the primary metric for power supply designers and in order to maximize power density it’s sometimes necessary to choose faster switching frequencies for modulation schemes. Power delivery systems use high-power semiconductor switches, such as silicon-based MOSFETs and new gallium nitride (GaN) and silicon carbide (SiC)-based MOSFETs, requiring a high-current isolated driver to control the switch. This improves system efficiencies but also produces higher noise transients that can cause signal loss or permanent damage from latch-up. The Si827x gate drivers protect power systems by offering exceptional immunity to these noise transients caused by high-speed switching.
The new drivers feature an EN (active high enable) pin instead of the typical DIS (active low) pin, under-voltage lockout (UVLO) fault protection, a de-glitch feature for filtering noisy inputs and highly precise dead time (DT pin) programmability. Using this DT feature, developers can precisely control the “dead time” between two switching drivers to optimize power system efficiency and safety.
Si827x Highlights include:
There’s a problem with the way we measure current in high-voltage systems. While inverters and high-power systems need current information to maintain safe operating conditions, improve system efficiency, and respond quickly to load changes; measuring current on a high-voltage rail can be a real challenge. Sensors have to be electrically isolated from the system controller, sensors have long delays limiting response time, accuracy over temperature ranges is difficult to maintain, and systems are noisy.
How does the Si8920 isolated amplifier solve for these challenges? Let’s take a look:
Sensors have to be electrically isolated from the system controller
Robust galvanic isolation keeps the controller safe even with working voltages up to 1200 V
Sensors have long delays limiting response time
Low signal delay means the controller can respond quickly with bandwidth of up to 750kHZ and response times with an unprecedented 0.75 µs signal delay
Accuracy over temperature ranges is difficult to maintain
Tiny offset (1 µV/°C) and gain drift insures accuracy over an entire temperature range of -40 to 125°C
Systems are noisy
Excellent transient noise immunity, with more than 25 years of field operation expected
In contrast with traditional amplifiers, the Si8920 is the industry’s fastest isolated current sense amplifier. It provides precise current shunt measurement for power control systems, including motor drivers and inverters.
Ideal use cases for the Si8920 include industrial motor drivers, solar inverters, high-voltage power systems, uninterruptible power supplies (UPS) and electric/hybrid-electric (EV/HEV) vehicle systems.
Here’s an example of an AC Motor Drive that uses the Si8920 to measure current both on the high-voltage DC Link (+), as well as on the legs of the motor.
For more information on the Si8920, visit our website.