Entries by admin

PCIe Gen 5 timing chips deliver power advantage for data centers

Comprehensive portfolio of timing solutions provides lowest-power PCIe clocks and buffers
By Carolyn Mathas, contributing writer
Silicon Labs claims the industry’s first comprehensive and compliant portfolio of timing solutions that delivers best-in-class jitter performance for the PCI Express (PCIe) 5.0 specification. The new portfolio includes the Si5332 any-frequency clock family, the Si522xx PCIe clock generators, and the Si532xx PCIe buffers.
Powered from 1.5-V to 1.8-V supply rails, the Si522xx and Si532xx devices are the industry’s lowest-power PCIe clocks and buffers. The Si522xx and Si532xx output drivers with Silicon Labs’ push-pull high-speed current steering logic (HCSL) eliminates the need for and cost of external termination resistors, required by conventional PCIe clocks using constant-current output driver technology.
Data center designers implementing PCIe Gen 5 tap into increased interconnect speeds between the CPU and workload accelerators, including GPUs, FPGAs, and dedicated accelerator solutions, on the way to 400G Ethernet.
The Si5332 any-frequency clock family generates PCIe Gen 5 reference clocks with jitter performance of 140 fs RMS and optimizes PCIe SerDes performance. These clocks generate any combination of PCIe and general-purpose frequencies. The Si522xx PCIe clock generators and Si532xx PCIe buffers are capable of two, four, eight, or twelve PCIe Gen 1-/2-/3-/4-/5-compliant outputs for use in PCIe data center application endpoints.
Si5332 clocks generate any combination of PCIe and general-purpose frequencies, providing clock tree consolidation for diverse applications.
Features include full compliance with PCIe Gen 5 Common Clock, Separate Reference No Spread (SRNS), and Separate Reference Independent Spread (SRIS) architectures. The devices do not require discrete power supply filtering components for easier PCB layout without board-level noise to degrade clock jitter performance. The devices are drop-in−compatible with PCIe Gen 1/2/3/4 designs for a seamless migration.
The Silicon Labs PCI Express clock jitter tool is updated to include the filters to accurately measure PCIe Gen 5 reference clock jitter. The utility is free and can be found at silabs.com/pcie-learningcenter.
Lead times for samples and production quantities of the Si5332 any-frequency clock and Si522xx PCIe clocks and Si532xx PCIe buffers are two weeks and four weeks, respectively. Si5332 pricing ranges from $4.25 for the six-output device to $4.90 for the 12-output device. Price ranges for the Si522xx are $1.27 for the two-output device to $2.76 for the 12-output device, and prices for the Si532xx range from $1.40 for the four-output device to $2.10 for the 12-output device, all in quantities of 10,000.
Three development kits and their respective costs include the Si5332 any-frequency clocks (Si5332-6EX-EVB at $149), Si522xx PCIe clocks (Si52204-EVB at $140), and Si532xx PCIe buffers (Si53208-EVB at $175).

How to maximize the wireless range of short-range devices with sub-GHz RF transmitters in your home

Maxim Integrated provides tips and techniques to maximize the wireless power range of sub-GHz short-range devices with RF communications in your home electronics environment
By Bonnie Baker and Martin D. Stoehr, Maxim Integrated
We live our lives in a wireless world, from our short-range radio toys to our garage door openers, which become our own personal internet of things encircling our entire home. These radio tools and toys connect our lives through short-range wireless transmitters and receivers. Each of these applications presents challenges for radio designers to overcome, from maximizing connection distances to grappling with the Wi-Fi or Bluetooth regulatory jungle (Fig. 1).
Fig. 1: A wireless home or building system becomes a radio jungle when communicating with all functions.
The license-free ultra-high frequency (UHF) sub-GHz short-range device (SRD) is a vital part of these wireless household links. To keep in step with the neighborhood, the number of SRDs within homes are quickly multiplying. However, SRD home systems encounter several challenges related to their communications range, such as proper accounting for the flat-ground/multi-path transmission phenomena, transmitter power, and receiver sensitivity.
This article focuses on the SRD transmission block by providing useful environmental transmission insights and techniques to increase transmission power, along with tips to reduce supply current.
UHF sub-GHz SRD networksShort-range radio devices can be unidirectional or bidirectional radio transmitters. The frequency band of SRD transmitters and receivers are commonly in the sub-GHz range, below those for competing wireless regulated technologies, such as Wi-Fi (900 MHz, 2.4 GHz, 5.9 GHz, and others) and Bluetooth (2.4 GHz to 2.4835 GHz).
The term SRD applies to low-power, sub-GHz radio devices designed to operate across reasonable distances of 100 m. A simple SRD system, such as a garage door opener, consists of a transmit-to-receive single channel with intelligence and power supplies on both sides (Fig. 2).
Fig. 2: An SRD block diagram contains an RF transmitter and receiver.
In Fig. 2, the communication between the transmitter and the receiver carries information from a simple button or switch. The bottom portion of Fig. 2 shows an SRD transmitter block that has a radio frequency (RF) transmitter, microcontroller, pushbuttons or switches, and a coin-cell battery. The top portion of Fig. 2 shows the SRD’s receiver block that has an RF receiver, microcontroller with a command module, and a power-supply block.
In the system shown in Fig. 2, the transmitter block (bottom portion) is battery-powered, requiring low-power components to support the longevity of the coin-cell battery, while still allowing the RF transmitter to send a signal strong enough to maintain a link over the required distance.
SRD communication linkThe SRD transmission channel resides at the ground level, as opposed to long-range, open-space transmissions. Consequently, there are two signal paths to consider in a typical SRD transmission (Fig. 3).
Fig. 3: Flat-ground multi-path graphic transmission dynamics.
In Fig. 3, the transmitter sends the signal to the receiver starting from the transmitter antenna (TX). The primary path to the receiver antenna (RX) is the direct path along which the signal travels a distance equal to d2 (blue line) or R.
Equations 1 and 2, the Friis calculation, assist in determining the direct-path transmission margin.   
Equation 1 calculates the signal transmission power. Notice that the power at the receiver drops by a factor of 1/d22.
Using a 434-MHz signal over a 100-m transmission path, the transmitter-to-receiver path attenuation is –62 dB.
A secondary signal path is generated through the flat-ground multi-path or ground-reflected route. This distance is equal to d3 + d4 and, in addition to the small change in phase from the extra distance, the ground reflection causes a 180° phase reversal. Losses from the multi-path signal further degrade the overall transmission power of the signal seen by the receiver.
The link budget spreadsheet (download) highlighted in the application note “Radio Link-Budget Calculations for ISM-RF Products” provides a reliable calculation of this multi-path signal loss.
Transmission lossesImprovements in the SRD communication range can be realized by making changes to the transmitter and receiver as well as making refinements to the antenna design. Signal attenuation occurs through faulty hardware connections, ill-designed antennas, a direct-path channel, or obstructions from physical structures. Fig. 4 illustrates a complete 433.92-MHz link budget for a 100-m transmission channel.
Fig. 4. Typical SRD 433.92-MHz link budget at 100 m, providing –110 dBm effective sensitivity.
In Fig. 4, the industrial, scientific, and medical radio band (ISM) signal power for a 434-MHz frequency transmission over a 100-m distance of a home SRD application has a direct-path attenuation of –65 dB. The RF environmental SRD variables included in a link budget calculation are transmitter power (TX), transmitter antenna gain (TX_Ant), direct-path attenuation (DP), multi-path attenuation (MP), attenuation from obstructions (OB), receiver antenna gain (RX_Ant), and the receiver margin (RX_SNR).
Starting with the transmitter in Fig. 4, the transmitter’s power amplifier has an output of 10 dBm. The signal then travels through an antenna (TX_Ant) that causes a signal attenuation of –17 dBi. The signal travels across the channel with two routes, the direct-path (DP) signal that accounts for 65 dB of attenuation and the multi-path (MP) route, which causes an additional 18 dB of attenuation. Physical obstructions take another 13 dB of power from the signal. Upon arrival at the receiver block, the RX antenna (RX_Ant) causes a 6-dB loss, which results in a total received signal strength of –109 dBm.
When using a receiver with a specified sensitivity level of –110 dBm, this system configuration provides only 1 dB of margin (RX_SNR) when attempting to decode the transmitted signal. In this example, the TX_Ant and RX_Ant values include connection filtering, losses, and impedance-matching errors.
The received signal strength (RSS) can be calculated by subtracting the loss due to each element from the original transmitted power (Equation 3).
The difference between the calculated RSS and the effective sensitivity of the receiver is the margin, or RX_SNR.
The often-overlooked variables in this calculation are the flat-ground multi-path and physical obstructions such as brick walls and interior walls. In the previous discussion, there is accommodation for both the flat-ground multi-path and physical obstructions. Looking at Fig. 4, what remains of the transmitted signal is a very small amount of RSS, which is prone to noise interference.
From a theoretical perspective, the link budget spreadsheet and its related application note, “Radio Link-Budget Calculations for ISM-RF Products,” are good starting points for learning about and calculating the SRD channel evaluation. As a radio system designer will find, this SRD system budget calculator helps determine several useful trade-offs such as receiver sensitivity versus estimated range.
Tricks of the tradeEnhancements to the wireless range offered by this system are possible with a higher power transmitter (TX) output, better antennas (TX_Ant, RX_Ant), and better receiver (RX) sensitivity.
Higher power transmitter: Higher power transmitters can effectively translate into more decibels at the receiver. Commonly, this increase in TX power translates into a requirement for more current from the transmitter power supply or battery. In turn, the increased current shortens the battery life or increases the remote package size with a larger battery. The MAX41460-MAX41464 family of transmitters, as examples, can provide an additional 6 dB of output power over conventional transmitters without compromising the device’s power-supply requirements.
The MAX4146x family of devices includes high-output-power, low-current transmitters with up to 16 dBm of transmitted power that run on a 3-V coin-cell battery. This is achieved while keeping the supply current below 12 mA in ASK modulation (434 MHz, 3.0 V) and below 12 mA for FSK modulation (434 MHz, 3.0 V), which has little to no impact on the power budget. The devices provide over 16-dBm output power with a high power match or by using “boost mode” with current typically below 45 mA.
These transmitters allow more than 30 m of extra range without any penalty for battery-powered systems. By using optimized high power matching and/or boost-mode operation, as much as 60 m of additional range can be realized.
Better antennas: A better antenna design typically involves a larger antenna size. Common SRD operating frequencies are 315 MHz, 434 MHz, or 868 MHz/915 MHz. For these frequencies, the ideal length of the antenna should be a ¼-wavelength antenna equating to 23.8 cm, 17.9 cm, or 8.6 cm/8.2 cm, inclusive. For small-form-factor, battery-powered transmitters, none of these lengths are visually appealing or practical, so the design ends up with a transmitter antenna that is smaller than ideal yet “good enough.”
On the receiver side, it is possible to find room for the larger antenna size. Again, for an omnidirectional, ¼-wavelength monopole antenna (PCB trace loop or bent-monopole), there is potential for signal gain rather than attenuation. Changes to the receiver antenna can improve the signal power in Fig. 4 from –6 dbi to 1 dBi or more.
Better RX sensitivity: Improvements to receiver sensitivity act as a direct improvement to the SNR or link margin of the system. A change in the RX sensitivity from –110 dBm to –115 dBm directly provides an additional 5 dB of SNR. The trade-off for this improved sensitivity typically comes at the expense of increased power-supply current. More sensitive SRD receivers usually impact the cost of the solution as well.
Overall, the sweet spot to increase the SRD system range hinges on design time, bill of material (BOM) cost, and power budgets. These considerations point to utilizing a higher-output power transmitter.
Fig. 5 shows an improved 433.92-MHz SRD system with better link margin (SNR) obtained by implementing all of these suggested improvements.
Fig. 5. Typical SRD 433.92-MHz link budget at 100 m provides a –116-dBm effective sensitivity.
The difference betweenFig. 4 and Fig. 5 is the use of a 16-dBm versus a 10-dBm transmitter, which not only provides an improvement in TX_Ant attenuation from –17 dBi to –15 dBi but an improvement in RX_Ant from –6 dBi to –5 dBi and an improved receiver sensitivity from –110 dBm to –116 dBm. All of these improvements increase the SNR from 1 dB to 16 dB.
ConclusionSRDs appear in a large variety of applications that need short-distance and low-power data transmission channels. In many instances, existing standards such as Wi-Fi or Zigbee are not appropriate primarily because of supply current requirements. These design constraints open the way for the use of SRDs. This article showed how to maximize transmission ranges using a high-gain, low-power RF transmitter.
Learn more:MAX41460 300MHz–960MHz ASK and (G)FSK Transmitter with SPI InterfaceMAX41461 300MHz–960MHz ASK Transmitter with I2C InterfaceMAX41462 300MHz–960MHz ASK Transmitter with I2C InterfaceMAX41463 300MHz–960MHz (G)FSK Transmitter with I2C InterfaceMAX41464 300MHz–960MHz (G)FSK Transmitter with I2C Interface
About the authors:Bonnie Baker is an electrical engineer who has written three analog design books, starting with “A Baker’s Dozen: Real Analog Solutions for Digital Engineering” (2005). In past roles, Burr-Brown, Microchip, Texas Instruments, and Maxim Integrated facilitated her involvement in analog design and analog systems for the last 30+ years. Bonnie holds a master’s degree in electrical engineering from the University of Arizona (Tucson, Arizona) and a bachelor’s degree in music education from Northern Arizona University (Flagstaff, Arizona). In addition to her analog design fascination, Bonnie has a drive to share her knowledge and experience through the authorship of over 500 articles, design notes, and application notes.
Martin D. Stoehr has been working in the analog and mixed-signal IC industry since graduating from the University of Colorado in 1994 with a BSEE in communication systems and control theory. For the past 18 years, he has been designing various board-level systems at Maxim Integrated, from fully automated bench test systems to characterization boards, evaluation kits, reference designs, and demonstrators. He is currently the manager, applications engineering, at Maxim Integrated. In 2014, Martin was awarded “Article of the Year” for 2013 from Elektronik Magazine for his article “Kurzstrecken-Funksysteme professionell entwickeln” (“Getting Started with a Radio Design”)[1]
1. Elektronik Magazine article “Kurzstrecken-Funksysteme professionell entwickeln” (English title: “Getting Started with a Radio Design”), “Article of the Year” for 2013, http://www.elektroniknet.de/elektronik/halbleiter/die-elektronik-autoren-des-jahres-2013-107374-Seite-4.html

10 popular LoRa add-on boards for SBCs

The LoRa boards allow makers to deploy their creations in genuinely remote areas without the need for constant servicing or battery replacement/recharging
By Cabe Atwell, contributing writer
Long range (LoRa) is fast becoming the communication protocol of choice for IoT projects, as it provides the flexibility of low power and great range — perfect for applications such as wildlife tracking and environmental monitoring. According to the LoRa Alliance, there are more than 100 IoT LoRa-based networks operating around the globe, and the number continues to rise.
Those numbers are due in part by the maker communities and the affordability of project platforms, such as single-board computers (SBCs) and LoRa add-on boards. The LoRa boards allow makers to deploy their creations in genuinely remote areas without the need for constant servicing or battery replacement/recharging. As you can imagine, there is an equal amount of different LoRa add-on boards as there are SBCs — each with the same functionality in the communication protocol but with various features. In this roundup, we will take a look at the more popular LoRa boards that are used to increase the functionality of different single-board computers.
Why not get your Dragino LoRa GPS HAT? (Image: Dragino)
Dragino’s LoRa GPS HAT for the Raspberry Pi is based on Semtech’s SX1276/SX1278 transceiver, which can handle 868-MHz/433-MHz/915-MHz frequencies with a 168-dB maximum link budget. The list of features for this board is extensive and includes 20-dBm −100-mW constant RF output vs. 14-dBm high-efficiency PA, a programmable bit rate of up to 300 kbps, and a low RX current of 10.3-mA (200-nA) register retention.
On the GPS side, the board offers a power acquisition of 25 mA, power tracking of 20 mA, a programmable bit rate up to 300 kbps, and an update rate of up to 10 MHz. It also features a timing accuracy of 1 PPS (out 10 ns), a velocity accuracy without aid @

Driver-monitoring systems need a new breed of IR-LED drivers

Automotive IR camera systems need to be small and efficient and capable of withstanding harsh environmental conditions
By Nazzareno (Reno) Rossetti and Yin Wu, Maxim Integrated
Driver-monitoring systems (DMS) are becoming common in modern automobiles. Infrared (IR) cameras, utilizing an IR-LED in combination with a photo sensor, help recognize the hazardous microsleep that can affect motorists. DMS is also an enabling technology for the advancement of autonomous vehicle (AV) driving. In situations in which the driver needs to take back control from the car, the monitoring system will give the driver adequate time to react.
All of these functions and their associated electronics must fit seamlessly inside the car, which creates the need for flexible, small, and efficient solutions. They must also be able to cope with harsh automobile electrical environments.
In this design solution, we review an IR camera system and discuss the shortcomings of a typical solution. Subsequently, we present an IR-LED driver IC that is flexible, compact, and efficient while interfacing directly to the car battery.
Fig. 1: Driver-monitoring system in action.
The infrared advantageSome key advantages of infrared light are its invisibility to the human eye and its ability to work day and night. In addition to DMS, IR cameras can also detect and classify pedestrians in darkness, through most fog conditions, and are unaffected by sun glare, delivering improved situational awareness that results in more robust, reliable, and safe advanced driver-assistance systems (ADAS) and AV solutions. Other ADAS applications include seat-occupancy recognition, night-vision systems, short-range detection of surroundings, and monitoring drivers’ blind spots.
Infrared cameraFig. 2 shows the main elements of an infrared camera. The IR-LED illuminates the target. The reflected light is collected by the image sensor (CCD or CMOS photodiode) and processed by the vision processor to determine the response to the situation at hand. 
Fig. 2: IR-LED camera for DMS.
Buck LED driver for DMSThe LED driver controls the IR light intensity and strobes it at the right frequency and duty cycle. Ideally, it must work directly off of the 12-V battery and withstand the harsh automotive environment.
Vehicles that employ start/stop technology experience large battery voltage dips when the engine starts, causing the battery voltage to drop well below the typical 12 V. Starting from cold conditions (cold-crank), the battery can dip as low as 4.5 V. Disconnecting the battery from the alternator during operation results in large voltage transients (dump) up to 60 V.
The automotive environment is also subject to electromagnetic interference (EMI) due to both external and internal sources. The “arc and spark” noise that comes from ignition components, motors, and similar pulse-type systems affects the supply voltage rails by producing disruptive undervoltages or overvoltages. The IR-LED buck converter, with its fast switching waveforms, should be able to mitigate any contribution to this noisy environment.
Given the typical forward voltage for an IR-LED diode of 2.4 V and a forward current of 1 A, a well-designed buck LED driver has enough headroom to be directly connected to the battery without the need for voltage boosting. It must also withstand dump voltage and introduce minimum electromagnetic noise.
Typical high-power buck IR-LED driver solutionA typical buck IR-LED driver solution is shown in Fig. 3. It utilizes an n-channel transistor (typical RDS(ON) = 0.3 Ω) and a non-synchronous architecture that relies on the Schottky diode (D) for current recirculation. The latter is a sure sign of an inefficient implementation.  
Fig. 3: Typical non-synchronous buck IR-LED driver.
Consider the typical automotive case in which the input voltage is the car’s 12-V battery and the output is the forward voltage of an IR-LED diode (2.4 V at 1 A). Here, the buck converter duty cycle is only 20%. This means that the MOSFET in Fig. 3 conducts for only 20% of the time (0.3 Ω at 1 A = 0.3 W), while the Schottky (0.5 V at 1 A = 0.5 W) conducts for 80% of the time. The total power dissipated in the power train is 0.46 W, mostly due to the Schottky diode. After accounting for switching and other losses, this solution barely reaches an efficiency of 80%.
Integrated synchronous rectification solutionAs an example, the MAX20050 synchronous buck LED driver is an ideal solution (Fig. 4). The device includes a unique spread-spectrum mode that reduces EMI at the switching frequency and its harmonics. With its 4.5-V to 65-V input supply range, the IC can easily operate under start/stop conditions and cold-crank. It can withstand battery load dump, making it ideal as the front-end buck converter connecting the IR-LED driver directly to the car battery. 
Fig. 4: IR-LED driver integrated, synchronous solution.
High efficiencyThe fully synchronous, 2-A step-down converter integrates two low-RDS(ON) 0.14-Ω (typ) n-channel MOSFETs, ensuring minimum ohmic losses. Here, 0.14-Ω RDS(ON) resistances will produce losses of only 140 mW, one-third of the previous case. This solution can easily achieve high efficiency. In Fig. 5, the synchronous solution achieves peak efficiency of 86% at 2.1 MHz and 92% at 400 kHz! Increasing the frequency to 2.1 MHz reduces the bill-of-materials (BOM) size at the expense of a few percentage points of efficiency while avoiding interference within the AM band.  
Fig. 5: Efficiency vs. LED current.
Small sizeThe high level of integration of this solution yields minimal PCB area occupation. Fig. 6 shows a non-synchronous buck converter IC requiring an external Schottky diode that occupies a PCB area almost double (78%) that of the single-chip solution.  
Fig. 6: Size comparison of non-synchronous vs. synchronous buck ICs.
FlexibilityFor maximum flexibility, a family of IR-LED drivers (Table 1) offers two operational frequencies to address efficiency-versus-size trade-offs and to provide internal-versus-external loop compensation for dynamic response optimization.
Table 1: IR-LED driver family.
The devices are specified for operation over the full –40°C to 125°C temperature range and are available in thermally enhanced 12-pin (3 × 3-mm) TDFN and 14-pin (5 × 4.4-mm) TSSOP packages with an exposed pad. 
ConclusionDriver-monitoring systems are appearing more frequently in modern automobiles. They must fit seamlessly within the automotive electronic system, creating the need for flexible, small, and efficient solutions. They must also cope with harsh automobile environments.
About the Authors:Nazzareno (Reno) Rossetti is an Analog and Power Management expert at Maxim Integrated. He is a published author who holds several patents in this field. He has a doctorate in electrical engineering from Politecnico di Torino, Italy.
Yin Wu, MBA, MSEE at Maxim Integrated, is a semiconductor business professional. He holds a master’s in business administration from Santa Clara University and a master’s degree in electrical engineering from San Jose State University.

AVX expands tantalum capacitor line with lowest profile of 0.5 mm

Enables small and thin designs for applications such as hearing aids, smart cards, wearables, and audio and power amplifier modules
By Carolyn Mathas, contributing writer
Adding to its line of low-profile TACmicrochip capacitors, AVX Corporation claims that its newest 3216-05 capacitor offers the lowest profile in the marketplace. At 0.5 mm high, the capacitor can be embedded in 0.8-mm-thick PCBs or in ultra-thin handheld devices. The most compelling benefit of the 3216-05 is that embedding the tiny capacitor frees up space, allowing designers to create small and thin designs for applications such as hearing aids, audio and power amplifier modules, near-field communication (NFC) systems, smart cards, wearable electronics, and industrial handheld devices.
Designing ultra-small and lighter electronic devices is simplified by embedding the AVX 3216-05, saving PCB space and weight.
The “I” case capacitor (EIA Metric 3216-05) features a capacitance value of 10 F and a voltage rating of 6.3 V. It enables designers to take advantage of capacitor space and weight reduction, as well as immunity to piezoelectric noise and higher stability, reliability, and temperature performance, all features of tantalum capacitors.
TACmicrochip capacitors feature an internal construction that is designed to eliminate the space consumption and thicker walls common to conventional molded tantalum capacitors. Tin-over-nickel terminations are standard in the series; however, gold-over-nickel options are also available. The operating temperature range is −55°C to 125°C.
The TACmicrochip capacitor family is now currently available in 11 case sizes (1005 to 3528), with heights ranging from 0.5 mm to 1.5 mm. Capacitance values range from 0.10 μF to 150 μF, and voltage ratings span from 2 V to 25 V.
For more information about the 3216-05 tantalum capacitor, including datasheets, technical information, and catalog, visit TACmicrochip.
To access the datasheet for standard and low-profile TACmicrochip capacitors, click here. The capacitors are currently available from Digi-Key Electronics, Mouser Electronics, and TTI, Inc.

LoRa dev kit for passive components simplifies IoT design

Raltron claims the industry’s first passive component LoRa development kit, packed with 60 components, including crystals, filters, and antennas
By Gina Roos, editor-in-chiefRaltron Electronics Corp. has claimed the industry’s first passive component LoRa Development Kit to make it easier to design IoT projects. The development kit consists of five different product families with a total of 60 passive components, including crystals, filters, and antennas. All of these devices are commonly used in product development based on the LoRa protocol and meet LoRa protocol requirements in Asia, Europe, and North America, said Raltron.
The passive components are designed to work with LoRa ICs from Semtech, Microchip, and STMicro. They were specifically selected to speed design for use in multiple markets based on available license-free radio bands.
The LoRa Development Kit includes three different-sized 32.000-MHz crystals that meet the frequency, thermal, and performance requirements of the LoRa protocol. The kit also supplies 32-MHz and 52-MHz temperature compensated crystal oscillators (TCXOs). The crystals offer low-G sensitivity and can be used in harsh environmental conditions such as acceleration forces.
To meet different regional LoRa frequency bands in Asia, Europe, and North America, the kit also includes 433-MHz, 868-MHz, and 915-MHz SAW filters as well as three different-sized stub antennas in the same frequencies. Also in the kit are 868-MHz and 915-MHz ceramic filters. The kit includes a memory stick with product specifications for each component.
The LoRa development kit is available for $99 each at authorized distributors including Dove Electronics and Arrow Electronics.

10 hot circuit protection devices

The chips safeguarding against overcurrent, overvoltage, and ESD are diversifying to better serve specialized use cases
By Majeed Ahmad, contributing writer
Circuit protection, an intrinsic part of electronics design, is continually incorporating advanced technologies while it serves specialized use cases with intelligent new features and compact footprints. Here is a selection of circuit protection devices — including fuses, circuit breakers, surge protection ICs, and electrostatic discharge (ESD) protection devices — that aid a broad array of designs ranging from automotive and industrial automation to home appliances and smartphones.
1. Supercapacitor auto-balancing
The supercapacitor auto-balancing (SAB) MOSFETs from Advanced Linear Devices (ALD) automatically balance the leakage current of each supercapacitor cell connected in a stack and thus balance voltage in each cell to prevent overvoltage damages in a variety of battery applications. It’s an active cell-balancing method that lowers the operating bias voltage of the leakier of two supercapacitors.
ALD also provides PCBs populated with SAB MOSFETs, and these boards can also be used for prototyping power designs. The SAB MOSFETs enable ultra-low-power operation and are highly suitable for applications that demand long battery life without maintenance or replacement. (See related article: Why MOSFETs are the best choice for automatically balancing supercapacitor leakage)
2. Battery protection IC for three- to five-serial-cell batteries
The protection IC for three- to five-serial-cell batteries from Japan’s ABLIC Inc. directly controls an external FET to protect batteries from being overcharged or over-discharged. The S-8245A/B/C/D Series also provides temperature protection while monitoring four temperature types.
Moreover, a power-saving function prevents dark current from causing loss of battery pack capacity during shipping. Next, the protection IC allows designers to configure protection circuits comprising six or more cells. The accuracy of the overcharge detection voltage is ±20 mV, while power consumption is 20 μA maximum.
3. PTC thermistor with highest voltage rating
Ametherm’s new series of ceramic PTC circuit protection thermistors claim to have combined the industry’s highest voltage rating of up to 1,200 Vdc with the lowest available resistance. The CL20 Series PTC thermistors provide stability and reliability in high-voltage applications and are optimized for inrush current limiting in pre-charge circuits and heater applications in addition to overcurrent protection.
These PTC thermistors also provide an alternative to fixed resistors. They offer five resistance values at 25°C from 7 W to 100 W while bringing tolerance down to 25% to accommodate a variety of pre-charge times. And the resistance values remain unchanged over the operating temperature range of –40°C to 110°C.
4. Protection thyristor for data lines
The new thyristor developed by Littelfuse Inc. provides safeguards for composite video blanking sync (CVBS) signal lines and ports from damaging overvoltage transients. The P0080S4BLRP protection thyristor facilitates data-line protection for a wide range of applications spanning from data and camera cables to set-top boxes and CAN bus systems.
The Littelfuse thyristor is designed for the protection of low-voltage signal-line applications. (Image: Littelfuse)
The P0080S4BLRP features minimum operating voltage of 6 V and 100-A 5/310-µS surge peak current capability. Moreover, the junction capacitance of less than 30 pF makes it highly suitable for 4.43-MHz CVBS signals, RS-484 and RS-323 data lines, and CAN Bus. The new thyristor offers higher power density in a smaller footprint, which also simplifies the board design with a compact and surface-mount solution.
5. Thermal cutoff for USB-C cables
Bourns Inc. has launched a new family of polymeric thermal cutoff (P-TCO) devices that protect USB-C cables from destructive and potentially dangerous thermal runaway events. The P-TCO-U series comes in a 1210 footprint, while the P-TCO-N series is available in a 1206 footprint.
The Bourns thermal cutoff device provides safeguards for a variety of temperature-current combinations. (Image: Bourns)
The ability of USB Type-C connector to facilitate power along with communication signals in extremely tight pin spacing heightens the potential risk of safety hazards from thermal runaway conditions triggered by dirt or liquid entering the connector. The P-TCO devices accommodate USB 3.2, 3.1, 3.0, and 2.0 protocols as well as other types of data and charging cables.
6. Surge protection for mobile devices
Kinetic Technologies has unveiled an overvoltage protection IC that it calls a “behind the port” solution for consumer products like smartphones and tablets. The KTS1656 is a single-input, dual-output overvoltage-protected load switch that dramatically raises the USB port’s VBUS protection by doubling the surge-voltage protection and protecting against reverse-voltage conditions.
The surge protection IC is rated for a DC input voltage of up to 28 V and is mainly targeted at smartphones, tablets, wearable devices, and industrial equipment. KTS1656 is IEC61000-4-5 surge-rated at more than ±200 V for protection against power-grid spikes.
7. PTC thermistor as a resettable fuse
Murata’s ceramic PTC thermistors are aiming to provide a resettable fuse function for a broad range of automotive and industrial automation equipment. The PRG series of devices have low and flat resistance curve so that acceptable levels of current can efficiently flow through them.
On the other hand, excessive current causes the thermistor element to heat up, so once a certain temperature point has been reached, there is a significant reduction in current flow. That’s how the thermistor operates as a resettable fuse and restores current flow once the device’s temperature has reduced.
8. Fuse varistor in smaller footprint
The EPCOS ThermoFuse family of fuse-protected varistors from TDK has added two new compact members: the NT14 and NT20 series. ThermoFuse varistors, uniquely designed disk varistors, are connected in series with a thermally coupled fuse and are, therefore, intrinsically safe. If the varistor overheats, the thermal fuse trips and isolates the varistor from the grid.
The NT14 series offers a maximum energy absorption of up to 220 J. (Image: TDK)
The NT14 series featuring a disk diameter of 14 mm is designed to absorb maximum surge currents with an 8/20-μs pulse of 6 kA at rated voltages between 130 VRMS and 680 VRMS. The NT20 series, featuring a disk diameter of 20 mm, has a surge-current capability with an 8/20-μs pulse of 10 kA at rated voltages between 130 VRMS and 750 VRMS.
9. Automotive TVS for higher voltages
The new transient voltage suppression (TVS) diodes from Littelfuse protect automotive circuitry from a higher level of voltage transients induced by lightning and other transient voltage events. The TPSMB Series expands the breakdown voltage range from 7.5 V to 550 V for unidirectional and 10 V to 650 V for bidirectional devices.
First, the advent of electric vehicles (EVs) and hybrid electric vehicles (HEVs) using higher voltages makes this AEC-Q101–qualified TVS diode highly suitable for automotive applications. Second, it circumvents the need to use multiple TVS diodes in series to provide adequate protection. And the use of a single component instead of multiple TVS diodes simplifies design and reduces board space.
10. TVS array for smartphones
ProTek Devices has released ultra-low-capacitance (0.6-pF) TVS arrays for overvoltage circuit protection in smartphones and other portable devices. The GBLCxxCIDFN series of TVS arrays is available in multiple voltages and is rated at 250-W peak pulse power per line for an 8/20-µs waveshape.
The new TVS arrays, available in a bidirectional configuration, are compatible with IEC requirements for the 61000-4-2 standard for ESD immunity and feature a low clamping voltage. The TVS device protects one power or I/O port and can be used as a replacement for an MLV varistor.

Three steps to optimize SiC power devices

Layout optimization is the foundation of the design to avoid parasitic components that add noise or spikes to the applied voltages or currents
By Maurizio Di Paolo Emilio, contributing writer
As new power transistors such as SiC MOSFETs are being increasingly used in power electronics systems, it has become necessary to use special drivers. Isolated gate drivers are designed for the highest switching speeds and system size constraints required by technologies such as silicon carbide (SiC) and gallium nitride (GaN) by providing reliable control over IGBTs and MOSFETs. The evolution of the architectures meets the new levels of efficiency and the stability of the timing performances, thus reducing the distortion of the voltage. This article uses ROHM Semiconductor’s power devices based on SiC technology as a reference point.
Why use SiC MOSFETs?SiC technology can provide several types of benefits, as shown in Fig. 1:
Fig. 1: Benefits derived from the adoption of SiC technology.
First, we have a lower intrinsic resistance of the material, which allows for smaller dice and ultimately smaller packages. This is a critical factor for complex components such as power devices, which generally include several layers in a bridge configuration. Moreover, a smaller die helps to optimize the internal layout better and reduces the parasitic capacitance.
A second benefit is a higher operative frequency. Higher working frequency, achievable through a better dynamic of the material and higher switching rate, allows the size reduction of passive components (coil inductors, filters, and transformers), the ripple, and, in some cases, the input and output capacitance.
A third benefit is related to the higher operating temperature due to the higher working temperature of SiC material (that can reach up to 200°C) and its better conductivity. Based on this, we can downsize the heat sink or, in some cases, simplify the cooling system. Sometimes it is even possible to migrate from a liquid to forced-air cooling system.
Challenges and optimization of SiC MOSFET driving circuitsHigher voltage:The first point is related to the higher gate voltage. Fig. 2 shows a comparison among different power devices: a SiC MOSFET, a power MOSFET, and a silicon IGBT.
Fig. 2: Comparison of different power devices.
From the output characteristics (referred to different manufacturers), we can observe that there is high variability in the voltage level. ROHM SiC MOSFETs, now in their third generation, have a typical gate-source voltage (VGS) of 18 V. We are now interested in checking what happens if we drive a SiC MOSFET with an incorrect voltage level: We will start from 18 V, progressively reducing the voltage to 16 V, 14 V, and even below this. This aspect is essential because a voltage dropout can also happen in the field, caused by supply voltage variability or by other factors. A test was conducted in the lab using the setup shown in Fig. 3:
Fig. 3: Test setup.
The measuring circuit is based on a booster configuration with an output power of 5 kW. Starting from a VGS of 18 V, the voltage is reduced step by step below 14 V. At 13.4 V, the test is stopped. Test results are visible in Fig. 4. As expected, RDS(on) increases as the gate voltage decreases. At about 14 V (referring to the device under test), we can observe a dramatic increase of temperature, and the test must be stopped as soon as possible before a breakdown (due to thermal runaway) occurs.
Fig. 4: RDS(on) and gate voltage.
This phenomenon is known because the RDS(on) temperature coefficient inverts its sign at about 12 V to 14 V. At 18 V, the temperature coefficient is positive. This means that when the temperature increases, an increase of RDS(on) occurs. At a low gate voltage, however, the temperature coefficient is negative, and when the temperature decreases, the RDS(on) decreases. To avoid thermal runaway, a minimum gate voltage of 14 V is requested for some categories of SiC MOSFETs.
Another big question is how to drive a SiC MOSFET correctly and whether we can use a silicon MOSFET for this purpose. Consider, for example, the power supply schematics of Fig. 5. With an input voltage of 700−1,000 VDC, it is tough to apply a silicon MOSFET, and in any case, we should use two MOSFETs in series to satisfy the voltage level for this application. The maximum voltage that the MOSFET can withstand can easily reach 1,350 V or above (1,000-V maximum input voltage plus the reflected voltage plus the surge voltage resulting from stray inductances).
Fig. 5: Driving a SiC MOSFET with a silicon MOSFET. A QR Flyback converter with three-phase input.
Instead of using two silicon MOSFETs, we could use just one SiC MOSFET (a 1,700-V type, for instance), but how to drive it? The answer is that we need a specialized IC. ROHM BD7682FJ is the first IC on the market optimized for SiC MOSFETs. It features a gate clamp at 18 V (avoiding a dangerous voltage), undervoltage lockout (UVLO) at 14 V, soft start (which helps to reduce the gate pulses), and a wide protection feature list.
Faster commutations:Concerning IGBT transistors, SiC MOSFETs are known to have a better dynamic, which means faster commutations. SiC MOSFETs have some tens-of-nanoseconds commutation, compared to the IGBT with some hundreds-of-nanoseconds commutation. To achieve this fast commutation, we must provide the total gate charge in less time. That means that we need a higher peak current in the gate driver. How much higher? As shown in Fig. 6, at least the same current of the IGBT is needed, or something higher.
Fig. 6: A SiC MOSFET offers faster switching compared to an IGBT. Due to faster switching time, SiC MOSFETs require a gate driver with a higher peak current.
Faster commutation also implies a higher dV/dt. Both dV and dt can be experimentally measured, as in the example shown in Fig. 7, where the IGBT and SiC MOSFET switching times are compared. As indicated in Fig. 7, a gate driver with a common-mode transient immunity (CMTI) of at least equal to (or higher) 100 V per nanosecond is needed.
Fig. 7: A lower threshold involves a clean and low parasitic PCB layout.
Lower threshold:An IGBT MOSFET has a threshold of about +5 V or even higher, whereas with a SiC MOSFET, the technology allows a lower threshold, about +1 V or +2 V (see Fig. 8). Moreover, this threshold decreases with increasing temperature due to a negative temperature coefficient for the threshold voltage. Therefore, in the gate driver design, we need to take care of this aspect because the noise on the gate can be dangerous. How can we control the noise and eliminate the parasitic effect? The first step is related to the PCB design. A good PCB design will minimize the following parameters:
The impedance of tracks from OUT to gate to the capacitor
The impedance of tracks from GND to source to the capacitor
The area of the high current path (in Fig. 8, the turn on the path is shown in red, whereas the turn off the path is shown in green)
Fig. 8: Miller effect occurring in a MOSFET half bridge.
The second step is related to the Miller clamp. Let’s consider the typical half-bridge MOSFET gate driver. A voltage change, VDS, occurs across the lower switch when turning on the upper-side MOSFET of the half-bridge (M2: OFF → ON). This generates a current (I_Miller), which charges the parasitic capacitance C of the lower MOSFET (see Fig. 9). This current flows via the Miller capacitance, the gate resistor, and the CGS capacitance. The faster VDS switches from low to high. If the voltage drop across the gate resistor exceeds the threshold voltage of the lower MOSFET, a parasitic turn-on known as the “Miller effect” occurs (M1 turns ON).
Fig. 9: Active Miller clamping.
The Miller effect can be avoided in two ways. One is the negative power supply (VEE) used to keep the MOSFET off. The second one is active Miller clamping, shown in Fig. 10.
This solution consists of the addition of a third internal MOSFET (M3) connected to the lowest potential in the driver circuit. When the MOSFET is being turned off, the clamp switch is activated as the gate voltage falls below a certain level to ensure that the MOSFET remains off throughout any ground bounce events or dVDS/dt transients. As indicated in Fig. 10, active Miller clamping can reduce a VGS increase by clamping the gate directly to ground or the negative power supply.
The third step is related to gate voltage oscillation. As you can see in Fig. 10, oscillation can be both positive and negative, producing noise. A proven workaround, in this case, is to add a capacitor between gate and source to improve the CGD/CGS ratio.
Fig. 10: An additional capacitor can reduce the gate voltage oscillation.
Because capacitors have an impact on switching time, this solution must be carefully evaluated. Based on the above-mentioned considerations, one device that meets these requirements is ROHM’s dedicated gate driver for SiC MOSFETs. The BM61S40RFV gate driver has UVLO at 14.5 V, overvoltage protection (OVP) at 22 V, a CMTI of 100 V/ns, and an output current of 4 A (it will be increased in future devices already planned in the product roadmap).
ConclusionThe foundation of the design is layout optimization. This is the first step to avoid parasitic components that add noise or spikes to the applied voltages or currents. The second step is the voltage level and the gate signal noise that must be checked under all operating conditions. The third step is to use dedicated devices for driving the SiC MOSFET.
This article was originally published on Power Electronics News.