Benchmarks for the IoT

Input Voltage

–Jeff Child, Editor-in-Chief

JeffHeadShot

I remember quite vividly back in 1997 when Marcus Levy founded the Embedded Microprocessor Benchmark Consortium, better known as EEMBC. It was big deal at the time because, while benchmarks where common in the consumer computing world of desktop/laptop processors, no one had ever crafted any serious benchmarks for embedded processors. I was an editor covering embedded systems technology at the time, and Marcus, as an editor with EDN Magazine back then, traveled in the same circles as I did. On both the editorial side and on the processor vendor side, he had enormous respect in the industry—making him an ideal person to spin up an effort like EEMBC.

Creating benchmarks for embedded processors was more complicated than for general purpose processors, but EEMBC was up the challenge. Fast forward to today, and EEEBC now boasts a rich list of performance benchmarks for the hardware and software used in a variety of applications including autonomous driving, mobile imaging, mobile devices and many others. In recent years, the group has taken on the complex challenge of developing benchmarks for the Internet-of-Things (IoT).

I recently had the chance to talk with EEMBC’s current president, Peter Torelli, about the consortium’s latest effort: its IoTMark-BLE benchmark. It’s part of the EEMBC’s IoTMark benchmarking suite for measuring the combined energy consumption of an edge node’s sensor interface, processor and radio interface. IoTMark-BLE focuses on Bluetooth Low Energy (BLE) devices. In late September, EEMBC announced that the IoTMark-BLE benchmark is available for licensing.

The IoTMark-BLE benchmark profile models a real IoT edge node consisting of an I²C sensor and a BLE radio through sleep, advertise and connected-mode operation. The benchmark measures the energy required to power the edge node platform and to run the tests fed by the benchmark. At the center of the benchmark is the IoTConnect framework, a low-cost benchmarking harness used by multiple EEMBC benchmarks. The framework provides an external sensor emulator (the I/O Manager), a BLE gateway (the radio manager) and an Energy Monitor.

Benchmark users interact with the DUT via an interface with which they can set a number of tightly defined parameters, such as connection interval, I²C speed, BLE transmission power and more. Default values are provided to enable direct comparisons between DUTs, or users can change them to analyze a design’s sensitivity to each parameter. IoTMark-BLE’s IoTConnect framework supports microcontrollers (MCUs) and radio modules from any vendor, and it is compatible with any embedded OS, software stack or OEM hardware.

It makes sense that IoT benchmarks focus on power and energy use. IoT edge devices need to work in remote locations near the sensors they’re linked with. With that in mind, Peter Torelli says that the benchmark measures everything inside an IoT system-on-chip (SoC)—including the peripheral I/O reading from the I2C sensor, the transmit and receive amplifiers in the BLE radio—everything except the sensor itself. Torelli says it was important to not use intelligent sensors for the benchmark, the idea being that its important that the MCU’s role performing communication be part of the measurement. Interestingly, in developing the benchmark, it was found that even the software stacks on IoT SoCs have a big impact on performance. “Some are very efficient when they’re in advertise mode or in active mode, and then go to sleep,” says Torelli, “And there are others that remain active for much longer times and burn a lot of power.”

Shifting gears, I want to take moment to praise long time columnist and member of the Circuit Cellar family, Ed Nisley. Over 30 years ago, Steve Ciarcia asked Ed to write a regular column for the brand-new Circuit Cellar INK magazine. After an even 200 articles, Ed decided to make his September column his last. Thank you, Ed, for your many years of insightful, quality work in the pages of this magazine. You’ll be missed. Readers can follow Ed’s continuing series of shop notes, projects and curiosities on his blog at softsolder.com.

Let me welcome Brian Millier as our newest Circuit Cellar columnist—his column Pickup Up Mixed Signals begins this issue. Brian is no stranger to the magazine, penning over 50 guest features in the magazine since the mid-90s on a variety of topics including guitar amplifier electronics, IoT system design, LCDs and many others. I’m thrilled to have Brian joining our team. With his help, we promise to continue fulfilling Circuit Cellar’s role as the leading media platform aimed at inspiring the evolution of embedded system design.

This appears in the November 340 issue of Circuit Cellar magazine

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EEMBC Releases SecureMark-TLS Benchmark for IoT Devices

EEMBC, an industry consortium that develops benchmarks for embedded hardware and software, today announced that its SecureMark-TLS benchmark is now available for licensing. Part of the SecureMark benchmarking suite for measuring the efficiency of cryptographic processing solutions, SecureMark-TLS focuses on the Transport Layer Security (TLS) protocol for internet of things (IoT) edge nodes.

SecureMark-TLS measures the performance and energy consumption of processors when implementing the TLS protocol on an edge device. The benchmark uses a common IoT cypher suite comprised of elliptic curve cryptography for key exchange and digital signing, and standard primitives such as SHA256 and AES128, in both CCM and ECB modes. The energy measurements are aggregated into a single final score that is representative of the TLS operations for the IoT edge node device.

“While security has become a paramount concern, implementing security comes at a price. SecureMark-TLS is intended to help system and silicon designers evaluate the performance and energy costs of implementing security,” said Jim McGregor, principal analyst at TIRIAS Research. “By using the most common encryption protocol for IoT edge nodes, SecureMark-TLS provides a new metric for comparing processors and SoCs.”

Other differentiators between products, such as cryptographic certifications (e.g., NIST or Common Criteria), countermeasures (xPA, fault injection), and hardware implementation specifics, can be described in a disclosure report. The disclosure report also includes a description of all relevant implementation details, such as the hardware device tested, the software library version used, compiler options and flags, and hardware crypto engine details if applicable.

“EEMBC’s SecureMark suite is designed to provide an industry-created and standardized tool that allows applications developers to analyze security implementations,” said Peter Torelli, EEMBC president and CTO. “Within the suite, we plan to support the testing and analysis of various security profiles for different application domains. For secure IoT communication, we are proud to introduce SecureMark-TLS as the first of these available for licensing.”

To request a SecureMark-TLS license, visit
https://eembc.org/memberinfo/requestinfo.php?reg=LIC&suite=securemark

EEMBC | www.eembc.org

Wide Range Power Monitor Embeds ADCs

Analog Devices, acquired earlier this year by Linear Technology, has announced the LTC2992, a wide range I²C system monitor that monitors the current, voltage and power of two 0 V to 100 V rails without additional circuitry. The LTC2992 has flexible power supply options, deriving power from a 3 V to 100 V  monitored supply, a 2.7 V to 100 V secondary supply, or from the on-board shunt regulator. These supply options eliminate the need for a separate buck regulator, shunt regulator or inefficient resistive divider while monitoring any 0 V to 100 V rail. The LTC2992 is a simple, single-IC solution that uses three delta-sigma ADCs and a multiplier to provide 8- or 12-bit current and voltage measurements and 24-bit power readings.

LTC2992The LTC2992’s wide operating range is ideal for many applications, especially 48V telecom equipment, advanced mezzanine cards (AMC) and blade servers. The onboard shunt regulator provides support for supplies greater than 100V and negative supply monitoring. The LTC2992 measures current and voltage either continuously or on-demand, calculates power and stores all of this information along with minimum and maximum values in I²C accessible registers. Four GPIOs can also be configured as ADC inputs to measure neighboring auxiliary voltages. Measurements are made with only ±0.3% of total unadjusted error (TUE) over the entire temperature range. If any parameter trips the user-programmable thresholds, the LTC2992 flags an alert register and pin per the SMBus alert response protocol. The 400 kHz I²C interface features nine device addresses, a stuck bus reset timer, and a split SDA pin that simplifies I²C opto-isolation.  The LTC2992-1 version offers an inverted data output I²C pin for use with inverting opto-isolator configurations.

The LTC2992 and LTC2992-1 are offered in commercial, industrial and automotive versions, supporting operating temperature ranges from 0°C to 70°C, –40°C to 85°C and –40°C to 125°C, respectively. Both versions are available today in RoHS-compliant, 16-lead 4mm x 3mm DFN and 16-lead MSOP packages. Pricing starts at $3.85 each in 1,000-piece quantities. Please visit www.linear.com/products/power_monitors for more product selection and information.

Summary of Features:

  • Rail-to-Rail Input Range: 0 V to 100 V
  • Wide Input Supply Range: 2.7 V to 100 V
  • Shunt Regulator for Supplies >100 V
  • Three Delta-Sigma ADCs with Less Than ±0.3% TUE
  • 12-Bit Resolution for Currents & Voltages
  • Four GPIOs Configurable as ADC Inputs
  • Shutdown Mode with IQ < 50 µA
  • I²C Interface
  • Split SDA Pin Eases Opto-Isolation
  • Available in 16-Lead 4mm x 3mm DFN & 16-Lead MSOP Packages

Analog Devices | www.analog.com

Linear Technology | www.linear.com

Dialog Semiconductor & Energous Announce Wireless Charging Partnership

Dialog Semicondcutor recently announced it will be the exclusive supplier of Energous Corp.’s WattUp RF-based wireless charging ICs. As part of the partnership, Dialog will make a $10 million investment in Energous and work to help drive broader adoption of wireless charging in products such as smartphones, IoT devices, wearables, and more.

The partnership combines Energous’s uncoupled wireless charging technology and Dialog’s power-saving technologies. WattUp technology uses Dialog’s SmartBond Bluetooth low energy solution as the out-of-band communications channel between the wireless transmitter and receiver. Dialog’s power management technology then distributes power from the WattUp receiver IC to the rest of the device. Dialog’s AC/DC Rapid Charge power conversion technology delivers power to the wireless transmitter.

Sources: Dialog Semiconductor and Energous

RMS Power Detector Offers High Accuracy Measurement

Linear Technology recently introduced the LTC5596, which is a high-frequency, wideband RMS power detector that provides accurate power measurement of RF and microwave signals independent of modulation and waveforms. It responds in an easy-to-use log-linear 29 mV/dB scale to signal levels from –37 to –2 dBm with accuracy better than ±1 dB error over the full operating temperature range and RF frequency range from 200 MHz to an unprecedented 30 GHz.Linear LTC5596

The LTC5596’s features and specs:

  • An extraordinarily wide bandwidth enables the detector to work seamlessly across multiple frequency bands using a common design with minimum calibration.
  • Operates from a single 3.3-V supply, drawing a nominal supply current of 30 mA.
  • Built-in improved ESD protection.
  • Two temperature grades: an I grade is designed for operation from –40° to 105°C case. A high-temperature H-grade has rated temperature from –40° to 125°C case.
  • Both temperature versions are available in a 2 mm × 2 mm plastic eight-lead DFN package.

The LTC5596 I-grade starts at $12.50 each in 1,000-piece quantities. The H-grade starts at $16.95 each. Both versions are available in production quantities.

Source: Linear Technology

Dialog Semiconductor Enters Gallium Nitride (GaN) Market

Dialog Semiconductor recently announced the upcoming availability of the DA8801, which is its first gallium nitride (GaN) power IC device, using Taiwan Semiconductor Manufacturing Corporation’s (TSMC) 650-V GaN-on-Silicon process technology. The DA8801 should initially find traction in the the fast-charging smartphone and computing adapter segment.

Along with Dialog’s digital Rapid Charge power conversion controllers, the DA8801 will enable more efficient, smaller, and higher power density adapters compared to FET-based options. The DA8801’s half-bridge integrates building blocks (e.g., gate drives and level shifting circuits) with 650-V power switches. Allows an up to 50% size reduction in power electronics

The DA8801 will be available in sample quantities in Q4 2016.

Source: Dialog Semiconductor

Multiport USB Type-C Docking System

Texas Instruments recently introduced a multiport USB Type-C and Power Delivery (PD) minidock reference design, which you can power it via a traditional power adapter, USB Type-C adapter, or notebook computer. The reference design—which that provides audio, USB data, power, and video support—offers a fully tested plan for a compact 2” × 4” dock.TI usb type c

A TPS65982 USB Type-C and PD controller sits at the core of the USB Type-C and Power Delivery Minidock. It enables dual-role port USB Type-C functionality, and thus it’s capable of delivering 60 W of power and supporting DisplayPort Alternate Mode and USB data transmission. In addition, the design features the TPS65986 USB Type-C and PD controller, an HD3SS3212 SuperSpeed multiplexer, a TUSB321 dual-role port controller, and an HD3SS460 Alternate Mode multiplexer, which work together to provide dual-role port capability for power, data, and video transfer.

Features, specs, and benefits:

  • Bidirectional power and data transfer
  • Smallest solution size enables you to develop up to 50% percent smaller docking stations compared to similar systems.
  • DisplayPort and High-Definition Multimedia Interface (HDMI) design flexibility
  • Fast development time: All integrated circuits (ICs) within the design are compliant with the current USB Type-C and PD standards, simplifying and speeding engineers’ design cycles.
    Simple implementation

The minidock TI Designs reference design (TIDA-01243) is now available for download. Additionally, an evaluation module allows designers to quickly evaluate and implement their minidock designs. The USB-CTM-MINIDK-EVM costs $499.

Source: Texas Instruments

Qi-Certified, 15-W Wireless Power Transmitter

Texas Instruments now offers the industry’s first WPC v1.2 Qi-certified, 15-W wireless power transmitter. Intended to deliver high-power wireless charging to industrial systems (e.g., hand-held medical devices), the bq501210 enables 84% system efficiency with significantly less thermal dissipation.TI bq501210

The bq501210’s features, benefits, and specs:

  • Fixed-frequency operation enables 15-W efficiency and reduces electromagnetic interference (EMI).
  • Fast-charging capability enables the transfer of up to 10 W to compatible receivers, including currently available fast-charging devices.
  • The High-Voltage Dedicated Charging Port (HVDCP) protocol negotiates with capable AC/DC wall adapters to adjust the input voltage.

The bq501210 transmitter is shipping in volume production. It comes in a 9 mm × 9 mm VQFN package and costs $3.75 in 1,000-unit quantities. An evaluation module (bq501210EVM-756) is available for $149.

Source: Texas Instruments

All-in-One Comprehensive Power Delivery Compliance Tester

Saelig Company recently announced the MQP Packet-Master USB-PDT all-in-one comprehensive Power Delivery Compliance Tester. Intended for testing protocol, measuring transmitter signal quality, receiver quality and interference rejection, and power load testing, the USB-PDT s a complete compliance tester and development tool for USB power delivery, incorporating analyzer, exerciser, compliance tester, PD VBUS generator, PD VBUS load, VBUS voltage, and current monitor functions. The unit performs comprehensive PHY, protocol and power compliance tests on PD devices, and PHY and protocol tests on PD cable marker chips.Saelig usb pdt

The base unit, which incorporates a plug-in module design, comes with GraphicUSB, an easy-use graphical Windows application for driving and reporting on the compliance tests and capturing and displaying every detail of power delivery interactions. “Power Delivery” is a specification allowing USB ports to provide power in a more flexible and adaptable way. The industry standard BMC version uses two-way signaling on the CC wire of a USB C-cable. The Packet-Master USB-PDT behaves as one end of a power delivery link. It can emulate the behavior of an initial Downstream Facing Port (DFP) or Upstream Facing Port (UFP) in controlled ways, and can confirm the responses of the connected Unit Under Test (UUT). It is also designed to perform all the required protocol and PHY Compliance Tests on Electronic Cable Markers.

The Packet-Master USB-PDT’s plug-in module design concept has the following advantages for connecting test devices:

  • USB-PD connectors can be damaged by handling. If a connector becomes damaged, you can simply replace the plug-in module.
  • The Type-C receptacle on the plug-in is itself a user-replaceable item.
  • Different connector styles are available for USB-PD use. Swapping plug-in modules provides the flexibility required.

Designed USB experts MQP Electronics, the USB-PDT will be available from Saelig in Q1 2016.

Source: Saelig Company

New Power Supply Chip Attacks “Vampire Power”

STMicroelectronics recently announced a new power supply chip intended to minimize “vampire power.” Meeting the international specification for zero standby power, the new chip offers an intelligent way of of managing the wake-up function in appliances, industrial, and lighting equipment.

STmicro’s new VIPer0P IC helps reduce wasted power and CO2 emissions by enabling effective zero-power standby in appliances. With its patented smart-management capability, the VIPer0P enables an appliance to be woken up from standby via a touchscreen or remote control. In addition, the IC consumes less than 5 mW in idle mode (at 230-VAC supply).

An off-line power-converter IC, VIPer0P—which can be configured as a flyback, buck, or buck-boost switched-mode power supply (SMPS)—is the latest member of STMicro’s VIPerPlus series. Additional features include integrated high-voltage startup circuitry, error amplifier with 1.2-V reference and separate ground for direct feedback connection, and a sense-FET for energy-efficient current sensing. These simplify design and minimize external components thereby saving bill-of-materials costs and board space. In addition, VIPer0P’s self-supply design simplifies transformer selection by eliminating any need for an auxiliary winding.

Source: STMicroelectronics

Power Over Ethernet Solutions

Powering devices over Ethernet cabling seems easy, but there’s more to it
than meets the eye. In this article, Eddie Insam explains how it all works.

So you’ve designed a brand new Ethernet-based device. Perhaps it’s a clock, a weather sensor, or an industrial controller device. You plan to hang it proudly on your wall and connect it to a RJ-45 wall socket. But how are you going to power it? Where will the system get its juice? Surely, you aren’t going to disgrace your design with a brick wart. There must be a better way!

Why not feed power over the CAT-5 cable? Well, you’re not the first person to consider this technique.

The D-Link DWL-P50 is a ready-togo module. Ethernet in, Ethernet out, and a choice between 12- and 5-VDC outputs.

Photo 1: The D-Link DWL-P50 is a ready-togo module. Ethernet in, Ethernet out, and a choice between 12- and 5-VDC outputs.

Standard CAT-5 cable has four pairs, and only two are used for data in a typical 10- or 100-Mbps installation (see Figure 1a). So, it sounds obvious to stick a few DC volts down the spare pairs. Oh, yes. But hang on, life is never so simple. This is technology, remember? There has to be a catch somewhere. So, sit down and relax, I have the story.

Standard 10- and 100-Mbps Ethernet devices use just two of the four available pairs. The spare wires can be used to transmit power to the remote. Two possible methods are shown (b and c). But watch out! The power source must be smart enough to detect shorts and overloads and to avoid damaging components at the far end.

Figure 1: Standard 10- and 100-Mbps Ethernet devices use just two of the four available pairs. The spare wires can be used to transmit power to the remote. Two possible methods are shown (b and c). But watch out! The power source must be smart enough to detect shorts and overloads and to avoid damaging components at the far end.

It may not come as a surprise that the wise men at the IEEE thought about this for a while and came up with a standard (IEEE 802.3af). This standard has been around since 1999, but progress has been relatively slow. It started to take off only recently, mainly because of the availability of inexpensive specialist components. Tom Cantrell and Jeff Bachiochi have covered some of the available components and modules (Circuit Cellar 165 and 187). A wide range of parts are now available, including dedicated switching transistors, isolation transformers, and high-quality nonsaturating magnetics, making power over Ethernet (PoE) a practical proposition.

TECHNICALITIES
The IEEE document covers two main methods for sending power down the CAT-5 wire. One involves using the spare pairs. The other involves sharing with the existing data lines using center-tapped transformers (see Figures 1b and 1c). The latter method is beneficial when spare cable capacity isn’t available.

The method involving spare pins allows a decent amount of current to be drawn because the two spare pairs are paralleled together to increase capacity by reducing the total DC resistance. The present IEEE specifications allow up to 13 W of power to be transferred this way. This may not be enough for some heavy-duty devices, but it’s quite acceptable for medium-size and small items such as TV cameras and VoIP phones. An updated PoePlus standard is currently being considered. This will allow for up to 30-W capacity, while still remaining backwards compatible.

Transmitting power with center-tapped transformers is more limited. Pulse transformers and other magnetics in the Ethernet controller must be designed to take the full DC power load current without saturating. That isn’t an easy task for miniature surface-mounted components. The advantage of this alternative is that it leaves the extra pairs alone, an essential consideration in higher-speed gigabit Ethernet, which requires all four pairs to carry data.

POWER SUPPLY
Why can’t you just stick any old power supply across the spare wires? Because you don’t know what’s at the remote end, and you may run the risk of blowing up sensitive equipment. If you don’t believe me, take a look at Figure 2, which is a typical Ethernet terminator. This kind of circuitry is sometimes contained within a single metal enclosure called a MagJack.

This is a typical Ethernet termination. The resistors strapped to the spare data pins and center taps are there to balance the line and to reduce noise. They can quickly flash to smithereens in true Harry Potter style if any unmanaged DC power is placed on the cable.

Figure 2: This is a typical Ethernet termination. The resistors strapped to the spare data pins and center taps are there to balance the line and to reduce noise. They can quickly flash to smithereens in true Harry Potter style if any unmanaged DC power is placed on the cable.

Note the two 50-W resistors R3 and R4 across the center taps of transformers T3 and T4. They are branched in series to form an effective 150-W DC load across the input lines. Also note the two 50-W resistors R1 and R2 right across pins 7 and 8 and 4 and 5. These present a controlled impedance load to the otherwise non-terminated wires. They are there for robustness and noise reduction. This hookup is sometimes known as a Bob Smith termination.

If you connect a 48-VDC raw supply into such a socket, you will be driving a good third of an amp through these tiny resistors. This is guaranteed to vaporize them to kingdom come. Tiny SMD resistors are not built for such treatment.

Download the entire article.

Quad Bench Power Supply

The need for a bevy of equipment for building and testing presents a problem: how to deliver an adequate power supply while keeping workbench clutter to a minimum. Brian decided to tackle this classic engineering conundrum with a small, low-capacity quad bench power supply.

To the right of the output Johnson posts are the switches that set the polarity of the floating supplies—as well as the switch that disconnects all power supply outputs—while leaving the unit still powered up.

To the right of the output Johnson posts are the switches that set the polarity of the floating supplies—as well as the switch that disconnects all power supply outputs—while leaving the unit still powered up.

In “Quad Bench Power Supply,” Millier writes:

I hate to admit it, but my electronics bench is not a pretty sight, at least in the midst of a project anyway. Of course, I’m always in the middle of some project that, more often than not, contains two or three different projects in various stages of completion. To make matters worse, most of my projects involve microchips, which have to be programmed. Because I use ISP flash memory MCUs exclusively, it makes sense to locate a computer on my construction bench to facilitate programming and testing. To save space, I initially used my laptop’s parallel port for MCU programming. It was only a matter of time before I popped the laptop’s printer port by connecting it to a prototype circuit with errors on it.

Fixing my laptop’s printer port would have involved replacing its main board, which is an expensive proposition. Therefore, I switched over to a desktop computer (with a $20 ISA printer port board) for programming and testing purposes. The desktop, however, took up much more room on my bench.

You can’t do without lots of testing equipment, all of which takes up more bench space. Amongst my test equipment, I have several bench power supplies, which are unfortunately large because I built them with surplus power supply assemblies taken from older, unused equipment. This seemed like a good candidate for miniaturization.

At about the same time, I read a fine article by Robert Lacoste describing a high-power tracking lab power supply (“A Tracking Lab Power Supply,” Circuit Cellar 139). Although I liked many of Robert’s clever design ideas, most of my recent projects seemed to need only modest amounts of power. Therefore, I decided to design my own low-capacity bench supply that would be compact enough to fit in a small case. In this article, I’ll describe that power supply.

MY WISH LIST

Even though I mentioned that my recent project’s power demands were fairly modest, I frequently needed three or more discrete voltage levels. This meant lugging out a couple of different bench supplies and wiring all of them to the circuit I was building. If the circuit required all of the power supplies to cycle on and off simultaneously, the above arrangement was extremely inconvenient. In any event, it took up too much space on my bench.

I decided that I wanted to have four discrete voltage sources available. One power supply would be ground referenced. Two additional power supplies would be floating power supplies. Each of these would have the provision to switch either the positive or negative terminal to the negative (ground) terminal of the ground-referenced supply, allowing for positive or negative output voltage. Alternately, these supplies could be left floating with respect to ground by leaving the aforementioned switch in the center position.

This arrangement allows for one positive and two positive, negative or floating voltage outputs. To round off the complement, I added Condor’s commercial 5-V, 3-A linear power supply module, which I had on hand in my junk box. Table 1 shows the capabilities of the four power supplies.

I wanted to provide the metering of voltage and current for the three variable power supplies. The simultaneous voltage and current measurement of three completely independent power supplies seemed to indicate the need for six digital panel meters. Indeed, this is the path that Robert Lacoste used in his tracking lab supply.

As you can see, there are four power supplies. I’ve included all of the information you need to understand their capabilities.

As you can see, there are four power supplies. I’ve included all of the information you need to understand their capabilities.

I had used many of these DPM modules before, so I was aware of the fact that the modules require their negative measurement terminal to float with respect to the DPM’s own power supply. I solved this problem in the past by providing the DPM module with its own independent power source. Robert solved it by designing a differential drive circuit for the DPM. Either solution, when multiplied by six, is not trivial. Add to this the fact that high-quality DPMs cost about $40 in Canada, and you’ll see why I started to consider a different solution.

I decided to incorporate an MCU into the design to replace the six DPMs as well as six 10-turn potentiometers, which are also becoming expensive. In place of $240 worth of DPMs, I used three inexpensive dual 12-bit ADCs, an MCU, and an inexpensive LCD panel. The $100 worth of 10-turn potentiometers was replaced with three dual digital potentiometers and two inexpensive rotary encoders.

Using a microcontroller-based circuit basically allows you to control the bench supply with a computer for free. I have to admit that I decided to add the commercial 5-V supply module at the last minute; therefore, I didn’t allow for the voltage or current monitoring of this particular supply.

THE ANALOG CORE

Although there certainly is a digital component to this project, the basic power supply core is a standard analog series-pass regulator design. I borrowed a bit of this design from Robert’s lab supply circuit.

Basically, all three power supplies share the same design. The ground-referenced power supply provides less voltage and more current than the floating supplies. Thus, it uses a different transformer than the two floating supplies. The ground-referenced supply’s digital circuitry (for control of the digital potentiometer and ADC) can be connected directly to the MCU port lines. The two floating supplies, in addition to the different power transformer, also need isolation circuitry to connect to the MCU.

Figure 1 is the schematic for the ground-referenced supply. As you can see, a 24VCT PCB-mounted transformer provides all four necessary voltage sources. A full wave rectifier comprised of D4, D5, and C5 provides the 16 V that’s regulated down to the actual power supply output. Diodes D6, R10, C8, and Zener diode D7 provide the negative power supply needed by the op-amps. …

The ground-referenced power supply includes an independent 5-V supply to run the microcontroller module.

The ground-referenced power supply includes an independent 5-V supply to run the microcontroller module.

MCU AND USER INTERFACE

As with every other project I’ve worked on in the last two years, I chose the Atmel AVR family for the MCU. In this case, I went with the AT90S8535 for a couple of reasons. I needed 23 I/O lines to handle the three SPI channels, LCD, rotary encoders, and RS-232. This ruled out the use of smaller AVR devices. I could’ve used the slightly less expensive AT90LS8515, but I wanted to allow for the possibility of adding a temperature-sensing meter/alarm option to the circuit. The ’8535 has a 10-bit ADC function that’s suitable for this purpose; the ’8515 does not.

The ’8535 MCU has 8 KB of ISP flash memory, which is just about right for the necessary firmware. It also contains 512 bytes of EEPROM. I used a small amount of the EEPROM to store default values for the three programmable power supplies. That is to say, the power supply will power up with the same settings that existed at the time its Save Configuration push button was last pressed.

To simplify construction, I decided to use a SIMM100 SimmStick module made by Lawicel. The SIMM100 is a 3.5″ × 2.0″ PCB containing the ’8535, power supply regulator, reset function, RS-232 interface, ADC, ISP programming headers, and a 30-pin SimmStick-style bus. I’ve used this module for prototypes several times in the past, but this is the first time I’ve actually incorporated one into a finished project. …

eded to operate the three SPI channels and interface the two rotary encoders come out through the 30-pin bus. As you now know, I designed the ground-referenced power supply PCB to include space to mount the SIMM100 module, as well as the IsoLoop isolators. The SIMM100 mounts at right angles to this PCB; it’s hard-wired in place using 90° header pins. The floating power supplies share a virtually identical PCB layout apart from being smaller because of the lack of traces and circuitry associated with the SIMM100 bus and IsoLoop isolators.

The SIMM100 module has headers for the ISP programming cable and RS-232 port. I used its ADC header to run the LCD by reassigning six of the ADC port pins to general I/O pins.

When I buy in bulk, it’s inevitable that by the time I use the last item in my stock, something better has taken its place. After contacting Lawicel to request a .jpg image of the SIMM100 for this article, I was introduced to the new line of AVR modules that the company is developing.

Rather than a SimmStick-based module, the new modules are 24- and 40-pin DIP modules that are meant to replace Basic Stamps. Instead of using PIC chips/serial EEPROM and a Basic Interpreter, they implement the most powerful members of Atmel’s AVR family—the Mega chips.

Mega chips execute compiled code from fast internal flash memory and contain much more RAM and EEPROM than Stamps. Even though flash programming AVR-family chips is easy through SPI, using inexpensive printer port programming cables, these modules go one step further by incorporating RS-232 flash memory programming. This makes field updates a snap. …

The user interface I settled on consisted of a common 4 × 20 LCD panel along with two rotary encoders. One encoder is used to scroll through the various power supply parameters, and the other adjusts the selected parameter. The cost of LCDs and rotary encoders is reasonable these days. Being able to eliminate the substantial cost of six DPMs and six 10-turn potentiometers was the main reason for choosing an MCU-based design in the first place.

Brian Millier’s article first appeared in Circuit Cellar 149.

OptiMOS Product Family Exceeds 95% Efficiency

Infineon Technologies recently launched the OptiMOS 5 25- and 30-V product family, the next generation of Power MOSFETs in standard discrete packages, a new class of power stages named Power Block, and in an integrated power stage, DrMOS 5×5. Together with Infineon’s driver and digital controller products the company delivers full system solutions for applications such as server, client, datacom or telecom.Infineon-OptiMOS

The newly introduced OptiMOS family offers benchmark solutions with efficiency improvements of around 1% across the whole load range compared to its previous generation, exceeding 95% peak efficiency in a typical server voltage regulator design. This improved performance is based for example on the reduction of switching losses (Q switch) by 50% compared to the previous OptiMOS technology. Thus, implementing the new OptiMOS 25 V would lead to energy savings of 26.3 kWh per year for a single 130-W server CPU working 365 days.

The launch of the OptiMOS product family is accompanied by the introduction of a new packaging technology offering a further reduction in PCB area consumption. It is used in the Power Block product family and in the integrated powerstage DrMOS 5×5 and offers a source down low-side MOSFET for improved thermal performance, with a reduction by 50% of the thermal resistance in comparison to standard package solution, such as SuperSO8.

Infineon`s Power Block is a leadless SMD package comprising the low-side and high-side MOSFET of a synchronous DC/DC converter into a 5.0 × 6.0 mm 2 package outline. With Power Block, customers can shrink their designs up to 85 percent by replacing two separate discrete packages, such as SuperSO8 or SO-8. Both, the small package outline and the interconnection of the two MOSFETs within the package minimize the loop inductance for best system performance.

OptiMOS 5 25V is also used in an integrated power stage, combining DrMOS 5×5, driver and two MOSFETs, for a total area consumption on the PCB equal to 25mm². The integrated driver plus MOSFETs solution results in a shorter design time and is easy to design-in. Additionally, the dovetailed power stage includes a high accurate temperature sense of +/-5°C (compared to +/-10°C of an external one) which enables higher system reliability and performance.

Samples of the new OptiMOS 25- and 30-V devices in SuperSO8, S3O8 and Power Block packages, with on-state resistances from 0.9 mΩ to 3.3 mΩ are available. Additional products with monolithic integrated Schottky-like diode and products in 30 V will be available from Q2 2015 onwards. DrMOS 5×5 will be released in Q2 2015. Samples are available.

Source: Infineon

Two Source/Measure Units for N6700 Modular Power Systems

Keysight Technologies recently added two source/measure units (SMUs) to its N6700 Series modular power systems. The N6785A two-quadrant SMU is for battery drain analysis. The N6786A two-quadrant SMU is for functional test. Both SMUs provide power output up to 80 W.

The two new SMUs expand the popular N6780A Series SMU family by offering up to 4× more power than the previous models. The new models offer superior sourcing, measurement, and analysis so engineers can deliver the best possible battery life in their devices. The N6785A and N6786A SMUs allow engineers to test devices that require current up to 8 A, such as tablets, large smartphones, police/military handheld radios, and components of these devices.keysight N6700

The N6780A Series SMUs eliminate the challenges of measuring dynamic currents with a feature called seamless measurement ranging. With seamless measurement ranging, engineers can precisely measure dynamic currents without any glitches or disruptions to the measurement. As the current drawn by the device under test (DUT) changes, the SMU automatically detects the change and switches to the current measurement range that will return the most precise measurement.

When combined with the SMU’s built-in 18-bit digitizer, seamless measurement ranging enables unprecedented effective vertical resolution of ~28-bits. This capability lets users visualize current drain from nA to A in one pass. All data needed is presented in a single picture, which helps users unlock insights to deliver exceptional battery life.

The new SMUs are a part of the N6700 modular power system, which consists of the N6700 low-profile mainframes for ATE applications and the N6705B DC power analyzer mainframe for R&D. The product family has four mainframes and more than 30 DC power modules, providing a complete spectrum of solutions, from R&D through design validation and manufacturing.

Source: Keysight Technologies 

Quad Channel DPWM Step-Down Controller

Exar Corp. has introduced the XR77128, a universal PMIC that drives up to four independently controlled external DrMOS power stages at currents greater than 40 A for the latest 64-bit ARM processors, FPGAs, DSPs and ASICs. DrMOS technology is quickly growing in popularity in telecom and networking applications. These same applications find value in Exar’s Programmable Power technology which allows low component count, rapid development, easy system integration, dynamic control and telemetry. Depending on output current requirements, each output can be independently configured to directly drive external MOSFETs or DrMOS power stages.EX045_XR77128

The XR77128 is quickly configured to power nearly any FPGA, SoC, or DSP system through the use of Exar’s design tool, PowerArchitect, and programmed through an I²C-based SMBus compliant serial interface. It can also monitor and dynamically control and configure the power system through the same I²C interface. Five configurable GPIOs allow for fast system integration for fault reporting and status or for sequencing control.  A new Arduino-based development platform allows software engineers to begin code development for telemetry and dynamic control long before their hardware is available.

The XR77128 is available in a RoHS-compliant, green/halogen free space-saving 7 mm × 7 mm TQFN. It costs $7.75 in 1000-piece quantities.

Source: Exar Corp.