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Industrial digital input chips provide serialized data by default. However, in systems that require real time, low latency, or higher speed, it may be preferable to provide level-translated, real-time logic signals for each industrial digital input channel.

So, some industrial digital inputs sample and serialize the state of eight 24-V current sinking inputs under SPI or pin-based (LATCH) timing control, allowing for readout of the eight states via SPI. A serial interface is used to minimize the number of logic signals requiring isolation, which is particularly beneficial in high channel count digital input modules.

Serialization of logic signals uses simultaneous sampling of the signals so that the signals become time quantized. This means that real-time information content is lost, which can be of concern in certain systems. Examples are applications where timing differences between switching signals are of concern, such as incremental encoders or counters.

These applications either necessitate the use of high-speed sampling with high-speed serial readout or the use of non-serialized parallel data, as provided by the MAX22195, an industrial digital input with parallel output. Using the MAX22190/MAX22199 industrial digital input devices with parallel operation provides the benefit of diagnostics and configurability.

This article delves into the characteristics, limitations, and design considerations regarding techniques for generating parallel logic outputs with industrial digital inputs.

Design details

The technique is based on repurposing the eight LED outputs to function as logic signals. LEDs serve to provide a visual indication of the digital input’s state—useful for installation, maintenance, and in service. The characteristics and specifications of industrial inputs are clearly defined in the IEC 61131-2 standard, with the output state being binary in nature: either on or off.

The MAX22190/MAX22199 chips feature energyless LED drivers that power the LEDs from the sensor/switch in the field, not drawing current/power from a power supply in the digital input module. These devices limit the input current to a level settable by the REFDI resistor. This is done to achieve the lowest power dissipation in the module.

For the common Type 1/Type 3 digital inputs, the input current is typically set to a level of ~2.3 mA (typ) to be larger than the 2.0 mA minimum required by the IEC standard. The ICs channel most of the ~2.3 mA field input (IN) current to the LED output pins, and only ~160 µA are consumed by the chip.

With the LED drivers being current outputs, not voltage, the current needs to be converted to voltage for interfacing with other logic devices like digital isolators and microcontrollers. Resistors are the simplest trans-resistance element for this purpose, as shown in Figure 1.

Figure 1 LED pins are used as voltage-based logic outputs. Source: Analog Devices Inc.

Using the LED output pins in this manner is not documented in the product datasheets. This article investigates the characteristics and possible limitations.

LED pin characteristics

When using ground-connected resistors on the LED pins to create voltage outputs, the following needs to be considered:

• What is the maximum voltage allowed on the LED pins?
• Is there interaction/feedback from the LED_ pin to the IN_ pin?
• Specifically, does voltage on the LED pins result in a change of the input current, as minimum current levels are mandated by the IEC standards?
• Do the LED output currents show undesired transient behavior, such as overshoots or slow rise/fall times?
• Are the LED outputs suitable for use as high-speed logic signals when the inputs switch at high rates?
• Are the LED outputs filtered (as programmable by SPI)?

The MAX22190/MAX22199 datasheets’ absolute maximum ratings specify the maximum allowed LED pin voltages as +6 V. This indicates that the LED pins are suitable for use as 5 V (and 3.3 V) logic outputs, with the caveat that the voltage may not be higher than 6 V.

The impact of the LED pin voltage on other critical characteristics needs to be evaluated. Of particular concern is the change of the input current with the presence of high LED pin voltages, as the current is specified by the standards. The critical case is with the field voltage close to the 11 V on-state threshold voltage, as defined for Type 3 digital inputs.

Figure 2 shows the measured field input current dependence on the LED pin voltage for three field input voltages close to the 11-V level: 9 V, 10 V, and 11 V. The 10-V and 9-V levels were chosen as these are within the transition region for Type 3 inputs, and their input currents have no defined minimum, while the minimum for the 11 V input case is 2 mA.

Figure 2 Field input current is dependent on the LED pin voltage. Source: Analog Devices Inc.

With the field voltage at the 11-V threshold, the blue curve shows that the input current starts decreasing when the LED voltage is higher than ~5.8 V. The current decrease is only 0.6% at 6 V. For cases of 9 V and 10 V, which are in the transition where the currents are not defined, the measurements show that the input current is still above 2 mA for up to 5.5-V inputs.

In conclusion, this shows that the MAX22190/MAX22199 will produce 5-V LED logic outputs (as well as lower voltage logic like 3.3 V) and still be compatible with Type 3 digital inputs. For Type 1 digital inputs, the case is trivial since the on-threshold is much higher at 15 V, meaning that the LED pins will also provide 5-V logic levels without any impact on the field input current.

Parallel operation example

Figure 3 shows a 10-kHz field input (yellow curve) with the resulting LED output voltage in blue. A 1.5-kΩ resistor was used on the LED output, which provides a 3.3 V logic signal. Glitch filtering was disabled (default bypass mode).

Figure 3 In 10-kHz switching, Channel 1 has field input and Channel 2 has LED output. Source: Analog Devices Inc.

Regarding the transient behavior of the LED output current under switching conditions, Figure 3 shows a case of 10-kHz switching. A 1.5-kΩ resistor was used to convert current to voltage. The scope shot illustrates that the LED outputs do not produce transient overshoots or undershoots that could damage logic input devices. The rise and fall times are fast and do not lead to signal distortion.

Using the SPI interface

The MAX22190/MAX22199 devices feature SPI-programmable filters to enable per-channel glitch/noise filtering. Eight filter time constants up to the 20-ms level are available as well as a filter bypass for high-speed applications. The selected noise filtering also applies to the LED outputs to make the visual representation consistent with the electrical signals.

Diagnostics are provided via SPI, like low power supply voltage alarms, overtemperature warnings, short-circuit detection on the REFDI and REFWB pins, and as wire-break detection of the field inputs.

The power-up default state of the register bits is:

• All eight inputs are enabled
• All input filters are bypassed
• Wire-break detection is disabled
• Short-circuit detection of the REFDI and REFWB (only MAX22199) pins is disabled

Hence, the SPI interface does not need to be used in applications that do not require glitch filtering (for example, for high-speed signals) and diagnostics. In cases where the per-channel selectable glitch/noise filtering is needed or diagnostic detection is wanted, SPI can be used.

The LED output waveform does not show overshoots or other undesired irregularities such as varying voltage in the on-state. This illustrates that the LED outputs can be used as voltage outputs. Its characteristics and limitations are investigated.

Glitch filtering

The MAX22190 and MAX22199 devices provide per-channel selectable glitch filtering. The following content demonstrates the effect of the glitch filters on the LED outputs by example of a 200-Hz switching signal with filter time set to 800 µs. Defined glitch widths were emulated by changing the duty cycle. Both positive and negative glitches were investigated.

Figure 4 shows an example of 750-µs positive pulses being filtered out by the 800-µs glitch filter. So, positive glitch filtering works both for the LED outputs as well as the SPI data.

Figure 4 Here is an example of positive glitch filtering. Source: Analog Devices Inc.

Negative glitches are, however, not filtered out at the LED outputs, as shown in Figure 5, where a 750-µs falling pulse propagates to the LED output. This differs from using the SPI readout, for which both positive and negative glitches are successfully filtered.

Figure 5 This image shows negative glitch filtering. Source: Analog Devices Inc.

Figure 6 shows the LED output signal with an 800-µs glitch filter enabled and input switching with a 50% duty cycle. The rising edges are delayed by ~770 µs while the falling edges show no delay. This illustrates that the filters do not work properly with the LED outputs.

Figure 6 This image highlights the filtering effect on LED output. Source: Analog Devices Inc.

High frequency switching

For applications with high switching frequencies, low propagation, or low skew requirements, glitch filtering would be disabled. In bypass mode (glitch filters) and 100-kHz input, the LED output results in the waveforms shown in Figure 7.

Figure 7 The 100-kHz input switching is shown with filter bypass. Source: Analog Devices Inc.

While the falling edges show low propagation delay of ~60 ns, the rising edges have significant propagation delay as well as jitter. The rising edge jitter is in the range of ±0.5 µs with an average propagation delay of ~1 µs. The rising delay and jitter are due to the ~1 MHz sampling documented in the datasheet. Sampling does not occur on the falling edges, hence the fast response.

This illustrates that the LED outputs have rise time/fall time skews of up to ~1.5 µs with jitter. Channel-to-channel skew is low on the falling edges but much higher on the rising edges. This could limit the use of the LED outputs in some applications.

Design considerations

This section discusses some considerations required when using the LED output pins as voltage outputs.

Ensure that the MAX22190/MAX22199 current-drive LED outputs are voltage limited to not exceed the safe levels of the logic inputs that they drive. While the REFDI resistor sets the field input current to a typical current level, the actual input current has a tolerance of ±10.6%, as specified in the datasheets. Thus, the voltage across the resistor will be in the ±10.6% range.

Logic inputs typically have tightly specified absolute maximum ratings, like VL + 0.3 V, where VL is the logic supply voltage. When interfacing two logic signals, a common VL supply is often used to ensure matching as standard logic outputs have push-pull or open-drain outputs whose maximum output voltage is defined/limited by a logic supply, VL.

One can make the typical LED pin’s output voltage lower to ensure that absolute maximum ratings are not exceeded for the input. Alternatively, one can consider that the LED pin’s ~2.3 mA output current will not damage a logic input, as these are commonly specified for tolerating much higher latch-up currents, in the 50 mA to 100 mA range. This needs to be verified for the device under consideration. The third, less attractive, option is to limit the voltage by clamping.

Standard logic outputs are push-pull and thus low impedance, providing high flexibility in driving logic inputs. In contrast, the LED outputs are open-drain outputs where the pull-down resistor with parasitic capacitance determines the switching speeds.

Without additional capacitors, switching rates of 100 kHz and higher are feasible.

The MAX22190/MAX22199 industrial digital inputs can be used as an octal input having eight parallel outputs, despite being documented for serialized data operation. To this purpose, the LED drivers, originally intended for visual state indication, are repurposed as voltage-based or current-based logic outputs. When using parallel operation in this manner, the use of the SPI interface is optional and provides all the diagnostics as well as device configurability with some limitations.

Wei Shi is an applications engineer manager in the Industrial Automation business unit of Analog Devices based in San Jose, California. She joined Maxim Integrated (now part of Analog Devices) in 2012 as an applications engineer.

Reinhardt Wagner was a distinguished engineer with Analog Devices in Munich, Germany. His 21-year tenure primarily involved the product definition of new industrial chips in the areas of communication and input/output devices.

Editor’s Note

This article was written in cooperation with Chin Chia Leong, senior staff engineer for hardware at Rockwell Automation.

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The post Design digital input modules with parallel interface using industrial digital inputs appeared first on EDN.

New Devices from MCU Leader Meet Demands for Performance and Compact Size; Offer Peripheral Set Targeted for Motor Control

Renesas Electronics Corporation introduced the RA2T1 microcontroller (MCU) group based on the Arm Cortex -M23 processor optimized for motor control systems. RA2T1 devices are specifically designed for single-motor applications such as fans, power tools, vacuum cleaners, refrigerators, printers, hair dryers and many more.

Feature Set Optimized for Motor Control

The new RA2T1 devices include a number of features designed to enhance motor control function, specifically in single-motor systems. One of the notable features is a 3-channel S&H function that simultaneously detects the 3-phase current values of Brushless DC (BLDC) motors. This method provides superior control accuracy as opposed to sequential measurement methods. The RA2T1 MCUs also offer complementary Pulse Width Modulation (PWM) function of the timer, which enables automatic insertion of dead time and generation of an asymmetric PWM. This function is optimized for inverter drive, which facilitates control algorithm implementation.

The RA2T1 devices offer safety features that are critical in motor control applications. They provide a Port Output Enable function and a high-speed comparator that work together to quickly shut off the PWM output when an overcurrent is detected. The shutdown state can be selected according to the inverter specifications.

Renesas Leadership in Embedded Processing for Motor Control

Renesas has shipped motor-control specific MCUs for over 20 years. The company ships over 230 million motor control embedded processors per year to thousands of customers worldwide. In addition to multiple RA MCU groups, Renesas offers motor-control specific devices in its 32-bit RX Family, its 16-bit RL78 MCUs and its 64-bit RZ MPUs.

“Customers have trusted Renesas motor control solutions for many years across thousands of systems,” said Daryl Khoo, Vice President of Embedded Processing Marketing Division at Renesas. “The RA2T1 MCUs enhance our leadership in this area with market-leading technology, low-power operation, and legendary Renesas quality and safety standards for single-motor systems.”

Key Features of the RA2T1 Group MCUs

• Core: 64 MHz Arm Cortex-M23

• Memory: 64KB Flash, 8KB SRAM, 2KB Data Flash
• Analog Peripherals: 12-bit ADC with 3-channel Sample and Hold, temperature sensor, internal reference voltage, 2-channel high-speed comparators
• System: High-, mid- and low-speed On-chip Oscillators; clock output; power-on reset; voltage detection; data transfer, event link and interrupt controllers; low-power modes
• Safety: PWM forced shutdown, SRAM parity error check, ADC self-diagnosis, clock frequency accuracy measurement, illegal memory access detection
• Operating Temperature Range: Ta = -40°C to 125°C

• Operating Voltage: 1.6V to 5.5V

• Packages: 48LQFP, 32-LQFP, 48-QFN, 32-QFN, 24-QFN (4mm x 4mm)

The new RA2T1 Group MCUs are supported by Renesas’ Flexible Software Package (FSP). The FSP enables faster application development by providing all the infrastructure software needed, including multiple RTOS, BSP, peripheral drivers, middleware, connectivity, networking, and security stacks as well as reference software to build complex AI, motor control and cloud solutions.

The post Renesas Debuts Best-in-Class MCUs Optimized for Single-Motor Applications Including Power Tools, Home Appliances and More appeared first on ELE Times.

The IoT Platform specifically designed for industrial applications, integrating Ethernet, RS485, CAN, and SD interfaces into a single system, and fully compatible with Arduino.

Nuvoton Technology introduced the NuMaker-UNO-M4 development board, an IoT platform based on the NuMicro M467 Ethernet / Crypto microcontroller series. It continues the classic design with industrial-grade standards, offering both ease of use and professional performance. The development board is fully compatible with Arduino pinout and additionally integrates essential industrial communication interfaces: Ethernet, RS485, CAN bus, and an SD card interface. It’s suitable for diverse application scenarios such as smart transportation, smart healthcare, smart industry, and smart homes.

The NuMaker-UNO-M4 features robust network connectivity, supporting wired connections and extendable wireless communication. It is equipped with an SD card interface for convenient long-term data logging and local storage, eliminating the need for additional data recording devices. This is particularly useful for applications requiring extensive data collection, such as smart agriculture, smart transportation, and health monitoring.

Powered by an Arm Cortex-M4 processor, it boasts hardware floating-point operations and DSP acceleration capabilities, supporting audio processing, vibration analysis, and small-scale AI applications, enhancing system performance and intelligence.

The NuMaker-UNO-M4 seamlessly integrates with the Arduino integrated development environment (IDE) and Nuvoton’s exclusive libraries, lowering development barriers. It also supports USB direct programming, streamlining the development process. Through Nuvoton’s comprehensive software development tools, combined with Nuvoton NuForum resources and a rich collection of example codes, even novice programmers can quickly generate code with the assistance of generative AI, accelerating development efficiency. This affordable and powerful industrial-grade development board offers developers an ideal choice that combines ease of use with professional capabilities.

Key Features of the NuMaker-UNO-M4 Development Board:

• Integrated Industrial Communication Interfaces: Ethernet, RS485, CAN bus, and SD card interface.
• Designed for Industrial-Grade Applications: Supports Modbus RTU/Modbus TCP, CAN, and MQTT applications.
• Suitable for Data Collection and Processing: Up to 1024 KB Flash Memory and 512 KB SRAM, with SD card support for long-term data logging.
• Compatible with Arduino Development Interface: Provides a high-quality and user-friendly development experience.
• Supports Network Functionality: Wired network support with optional WiFi / Sub-GHz connectivity for real-time monitoring and remote transmission.

The post NuMaker-UNO-M4: Industrial Intelligence Within Inches appeared first on ELE Times.

Leveraging its expertise in magnetic position sensors, Infineon Technologies AG has launched the third generation of the XENSIV 3D magnetic Hall-effect sensor family, comprising three product series: TLE493D-W3B6-Bx, TLE493D-P3B6, and TLE493D-P3I8. Developed in accordance with ISO26262, the sensor family provides integrated diagnostic functions to support functional safety applications up to ASIL-B. Due to their high flexibility, the devices are ideal for a wide range of industrial, consumer, and automotive applications, such as long-stroke linear position measurement, angular position measurement, automotive controls, and pedal or valve position sensing. In automotive applications, they enable control in the interior and under the hood, leveraging three-dimensional measurement functions and high-temperature resistance.

The new sensor family measures the magnetic field in three orthogonal dimensions and operates as an I²C or SPI bus slave. The devices offer enhanced magnetic performance and accuracy, with very low deviation over their lifetime (X/Y < 1.7% X-Y/Z = 6.75%). The 3D magnetic measurement principle and platform adaptability enabled by the device’s configurability allow for a reduction in the number of required components. Additionally, the system’s power consumption is very low due to its wake-up mode. The TLE493D-X3XX supports a supply voltage of 3.3 V and 5 V and offers 3D magnetic field measurement ranges of ±50 mT, ±100 mT, and ±160 mT. With these linear magnetic range options, the sensors are well-suited for controlling elements in infotainment and navigation systems and multifunction steering wheels. Furthermore, the devices operate reliably in a temperature range of -40°C to 150°C.

The post XENSIV magnetic 3D sensor enables high-precision position detection in automotive, industrial, and consumer applications appeared first on ELE Times.

Aeluma Inc of Goleta, CA, USA — which develops compound semiconductor materials on large-diameter substrates — has won new contracts with NASA and the US Navy that could accelerate development and commercialization for next-generation quantum and sensing systems...

Інститут кібернетики НАН України ім. В. М. Глушкова відзначений почесною відзнакою КПІ ім. Ігоря Сікорського kpi чт, 07/10/2025 - 22:32

NUBURU Inc of Centennial, CO, USA — which was founded in 2015 and develops and manufactures high-power industrial blue lasers — says that its stockholders have overwhelmingly approved key proposals in support of its financing strategy, a pivotal milestone in its strategic transformation for defense-tech and operational resilience through its Defense & Security Hub initiative...

Воркшоп з обчислювальних методів в системній інженерії на ФЕА Інформація КП чт, 07/10/2025 - 16:30

There are multiple means of generating analog sawtooth waveforms. Here’s a method that employs a single supply voltage rail and is not finnicky about passive component values. Figure 1 shows a pair of circuits that use a single 3.3-V supply rail, one producing a ground-referenced sawtooth and the other a supply voltage-referenced one.

Figure 1 The circuitry to the left of the 3.3 V supply implements a ground-referenced sawtooth labeled “LO”, while that to the right forms a 3.3V-referenced one labeled “HI”.

Wow the engineering world with your unique design: Design Ideas Submission Guide

For the LO signal, R1 supplies adequate current to operate U1. This IC enforces a constant voltage Vref between its V+ and FB pins. Q1 is a high beta NPN transistor which passes virtually all of R2’s current (Vref/R2) through its collector to charge C1 with a constant current, producing the linear ramp portion of this ground-referenced sawtooth. (U1’s FB current is typically less than 100 nA over temperature.) M1 is a MOSFET that is activated for 100 ns every T seconds to rapidly discharge C1 to ground. Its “on” resistance is less than 1 Ω and so yields a discharge that lasts more than 10 time constants.

The sawtooth’s peak amplitude A is Vref × T / (R2 × C1) volts, where Vref for U1 is 1.225 V. For a 3.3-V rail, the amplitude (A) should be less than an Amax of 2.1 V, which requires T to be less than a Tmax of  R2 × C1 × 2.1V / Vref. With the availability of a U1 Vref tolerance of 0.2% and a 0.1% tolerance for R2, the circuit’s overall amplitude tolerance is mostly limited by an at best 1% C1 combined with the parasitic capacitance of M1.

M2, C2, Q2, R3, R4 and U2 work much like the circuit just described, except that they produce an “upside-down” 3.3-V supply-referenced sawtooth. Both waveforms can be seen in Figure 2. With the exception of U2, the tolerance contributions of these components are those previously mentioned for the “right side-up” design respectively. U2’s reference current is typically less than 250 nA over temperature, but its Vref of 1.24 V has at best a 1% tolerance. Figure 2 depicts both sawtooth waveforms.

Figure 2 The waveforms shown have peak values which are slightly less than the largest recommended. The period T is 34 µs.

These circuits do not require any precision or matched-value passive components. And there is no need to coordinate these component values with any active component’s parametric values or with the switching period T, as long as T is kept less than Tmax. The only effect that the non-zero tolerances of the passive components and of certain active parameters has been on the peak-to-peak amplitude of the sawtooth waveforms.

Christopher Paul has worked in various engineering positions in the communications industry for over 40 years.

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The post Converting pulses to a sawtooth waveform appeared first on EDN.

Taking place from October 28 to 30, 2025 at the Shenzhen World Exhibition & Convention Center (Bao’an), NEPCON ASIA is the premier platform to discover the latest technologies and market trends, connect with new suppliers and products, and explore potential partnerships and distribution opportunities.

Featuring an ever-expanding showcase of automation equipment and technologies, the show empowers you to optimize your supply chain, reduce costs, and ensure quality and yield — all driving sustained growth in the electronics manufacturing industry.

Hundreds of New Product Launches

NEPCON ASIA 2025 will showcase hundreds of new products and solutions across SMT, testing and measurement, soldering, dispensing, semiconductor packaging, and automation. The show will feature over 600 leading exhibitors, including Yamaha, Hanwha, Fuji, Kurtz Ersa, Rehm, Tamura, Koh Young, TRI, ALEADER, Unicomp, Anda, and Axxon, connecting them with millions of buyers from high-growth sectors such as automotive electronics, semiconductors, and new energy.

The event aims to engage more than 2,000 buyers from emerging fields like low-altitude flight, embodied robotics, and AI, offering exhibitors invaluable exposure to new sectors.

Breakthrough Areas Driving Innovation

Several standout themed areas will debut, integrating industry resources and cutting-edge technologies, while showcasing packaging, testing, flexible manufacturing, assembly, and key components.

Key themed areas include:

• AI Smart Glasses Disassembly Area
• Flexible Manufacturing and Intelligent Transport System Area
• Low-Altitude Flight Components Disassembly Area
• Embodied Intelligence Robot Core Parts Disassembly Area
• Electronic Finished Products Automated Packaging Demonstration Area
• IGBT & SiC Packaging and Testing Demo Line

Conferences Empowering Industry Growth

NEPCON ASIA 2025 will host 40 high-level conferences covering advanced manufacturing, semiconductors, power electronics, robotics, and AI, empowering businesses to explore future technologies and seize new growth opportunities.

The SMTA South China High-Tech Workshop will feature global experts from China, the US, Japan, and Thailand, providing forward-looking insights for businesses.

The post NEPCON ASIA 2025: Innovating Smart Manufacturing Ecosystems and Bridging Global Opportunities appeared first on ELE Times.

👍🏰 Відкрито реєстрацію на молодіжні обміни «ВідНОВА:UA» – 2025! kpi чт, 07/10/2025 - 14:43

Discrete device designer and manufacturer Nexperia of Nijmegen, the Netherlands (which operates wafer fabs in Hamburg, Germany, and Hazel Grove Manchester, UK) has added two 1200V 20A silicon carbide (SiC) Schottky diodes to its portfolio of power electronics components...

Researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) laboratory in Germany have developed e-skin with magnetic-sensing capabilities, which they refer to as magnetoreception. They incorporated giant magnetoresistance effect and electrical resistance tomography technologies to achieve continuous sensing of magnetic fields across an area of 120 × 120 mm2 with a sensing resolution of better than 1 mm. Instead of focusing on sensor readings at specific points, the magnetoreceptor captures electrical resistance information across the entire measurement domain.

Read the full story at EDN’s sister publication, Planet Analog.

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The post How spiders and eels inspired a magnetoreceptive sensor appeared first on EDN.

КПІ ім. Ігоря Сікорського співпрацюватиме з Ю+МАГ kpi чт, 07/10/2025 - 10:25

For second-quarter 2025, AXT Inc of Fremont, CA, USA — which makes gallium arsenide (GaAs), indium phosphide (InP) and germanium (Ge) substrates and raw materials — expects preliminary revenue of $17.5–18m, below the guidance of $20–22m provided on 1 May and down from $27.9m a year ago. This is due primarily to slower-than-expected issuance of export control permits for its GaAs products in Q2 and a weaker demand environment in China...

submitted by /u/MrPicklePinosaur [link] [comments]

Студентка НН ІАТЕ Тетяна Гаврилюк про творчість, математику і страх kpi чт, 07/10/2025 - 01:35

Singapore’s Minister-in-charge of Energy and Science & Technology Dr Tan See Leng has officially opened the National Semiconductor Translation and Innovation Centre for Gallium Nitride (NSTIC (GaN)) as Singapore’s first national facility dedicated to gallium nitride...

Lively discussions have sprung up here in editor Aalyia Shaukat’s Design Ideas regarding the limitations and quirks of, and design tricks for, the current control topologies shown in Figure 1.

Figure 1 How to control amps of Iout with mA of Ic using legacy voltage regulators as current regulators where Iout  = (Vadj – IcRc)/Rs.

Wow the engineering world with your unique design: Design Ideas Submission Guide

Reader Ashutosh Sapre contributed a disturbing observation about the likely effect on regulator reference accuracy of temperature rise from self-heating, as illustrated in Figure 2.

Figure 2 LM317 reference variation with junction temperature as seen in page 5 of LM317 datasheet.

As shown in Figure 2, the temperature stability of these legacy devices is fairly good. Nevertheless, there are situations where the tempco can be problematic. 

For example, consider a scenario that begins with programming for 100% of full-scale output current (e.g., 1 A) so that regulator heat dissipation is high. Assume it’s maintained long enough for the regulator’s junction temperature to rise from 25oC to 125oC. Figure 2 predicts that this large temperature swing will cause Vref to drift from 1.25 V to 1.2375 V, causing the output current to decline by about 1% of full scale. 

This 1% corresponds to 10 mA out of 1000 mA and is somewhat less than 3 LSB of an 8-bit setting. That’s perhaps not great, but it’s not horrible either. But what if the output is then reprogrammed for 10% of full scale (e.g., 100 mA) while the regulator is still hot?

Then that 1% of full-scale error would become 10% of setting is what. It will manifest as a very lengthy thermal settling tail lasting many seconds as junction temperature gradually cools from 125oC, allowing Vref to (slowly) return to its initial 1.25 V and output current to settle at the correct 100 mA. It will happen eventually, but the time required will be objectionable. It may be unacceptable.

Fortunately, Ashutosh also contributed a simple and practical solution to the problem in the form of an auxiliary current shunt transistor. The shunt would allow most of the output current and, consequently, most of the self-heating to bypass the regulator entirely. This would leave its junction unheated and its Vref undrifted. Problem solved!

Or is it? Ashutosh also pointed out that the bypass transistor, while handily solving the thermal problem, would unfortunately also bypass other things. Specifically, the nifty fault protection features (e.g., automatic current limiting and overheating shutdown) built into LM317 and LM337 chips would be lost. While these assets could potentially be added to the transistor shunt, that would lose much of the simplicity that made it attractive in the first place.

So, I wondered if Ashutosh’s shunt idea could be implemented in a way that would inherently retain the desirable 317/337 features while staying simple. The obvious thing (I like obvious!) might be to just make the shunt out of another LM3xx. Figure 3 shows just that: A design that cross-connects complementary regulators using U1’s 317 for control and U2’s 337 for shunt. Control and shunt currents are then summed back together before passing through Rs to provide feedback to U1 where Iout = (I2 + I3) = (Vadj_U1 – IcRc)/Rs and I3 >> I2. Notice how the shunt gets turned “upside down.”

Figure 3 Cross connection reduces self-heating error because shunt regulator U2 carries most of the current, getting relatively hot, while U1, whose Vref is in control, stays relatively cool and accurate.

Figure 3’s U1 is connected mostly per Figure 1, except for Rx. The signal developed by Rx * I2 feeds U2’s ADJ pin so that when U1 input current I2 rises above about 10 mA, U2’s ADJ pin will drop enough to make it start conducting. This causes the I3 current component to rise and ultimately comprise the majority of total current I1 = I2 + I3. Thus, U2 dissipates most of the self-heating Watts, ensuring that U1 remains relatively cool and its Vref remains accurate. 

The 1N4001 in parallel with Rx protects Rx and U2’s ADJ pin if U2’s over-temp or over-current shutdown feature kicks in. That would leave U1 trying to shoulder the whole load, dropping enough voltage across Rx to likely damage U2 and fry the resistor. The diode prevents that. 

Figure 4 shows the idea working as a negative current source.

Figure 4 If the 317 and 337 swap places and the diodes reverse, Figure 3’s circuit can work for negative current, too.

If more current capability is needed, more U2 shunts and higher capacity diodes can be added (Figure 5).

Figure 5 Boost current handling capacity with beefier diodes and more U2s.

Figure 6 integrates this idea into a complete PWM controlled negative current source as detailed in: “A negative current source with PWM input and LM337 output.”

Figure 6 Negative current source circuit incorporates means for compensating component tolerances, including those of U1 and Z1 references. Note Rs = 1.1 Ω and should be rated for more than 1 W.

The one-pass adjustment sequence is:

1. Set Df = 100%
2. Adjust CAL pot for 1 amp output current
3. Set Df = 0%
4. Adjust ZERO pot for zero output current.

Done. Iout = 1.1 Df /Rs, where Df = PWM duty factor.

In closing, thanks go (again) to savvy reader Ashutosh for his suggestions and (likewise again) to editor Aalyia for the fertile DI environment she created, which makes this kind of teamwork workable.

Stephen Woodward’s relationship with EDN’s DI column goes back quite a long way. Over 100 submissions have been accepted since his first contribution back in 1974.

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• A negative current source with PWM input and LM337 output
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