September 2014

Interview with Umesh Mishra CTO of Transphorm

Unidirectional Voltage Translation

Designing Applications for Ultralow Power

Transphorm Redefines

POWER CONVERSION

Interview with Umesh Mishra Chairman and CTO of Transphorm

4

12

20

26

Not all portable systems are as simple as those shown previously in this series of articles. Here,

figure 1 shows a typical block diagram for a wearable electronic device. The complexity of the design is magnified by presence of a multitude of functional blocks and subsystems.

A logical approach is to divide the whole system into various subsystems and analyze their power consumption individually. This can also help simplify design of the power supply domain in such a way as to enable low-power functionality.

The power in the display and touch controller section is dominated by the backlight drive and the display itself. Most designs utilize a timer-based time-out and power-down mode for the display. Typically, after some fixed time (T1) the backlight drops to a 50 percent duty cycle and is turned off after additional time (T2) when the display itself is turned off. At this point, even the touch controller could be turned off or put in a power-down mode based on the usage scenario. This would let the designer draw a current profile for this block and subsequently a typical current.

Antenna

Sensor Actuators

Touch Screen

Touch Screen Module Display Module

Display

Controller

Main Processor

LED Drive

Battery

BatteryCharger

PowerSupply withRegulators

WirelessController

SensorExcitation

Touch ScreenController

BackLightLEDs

Wireless controllers like those for Bluetooth are generally designed for low power. They have a way of duty cycling between high- and low-power modes. The typical numbers in the wireless controller’s datasheet are the best assumption we can make about power consumption without actually profiling a system. However, remember to take into account the duty cycling nature of these devices between the different power modes.

Sensor currents are dominated by the excitation current and the power consumed by the analog front end (AFE). Devices like Cypress’s PSoC 4 have built-in analog capability like analog-to-digital converters (ADCs) and other AFE components. This allows designers to dynamically power down these blocks through firmware commands. This level of control and granularity can further improve efficiency in low-power designs.

For complex designs involving multiple controllers and multiple modes of operation, it might make sense to also design the power-supply circuits to accommodate different controllable power domains. This allows a single controller on a standby power domain to actively control the other domains. This type of architecture could be expensive to design but very low in power consumption.

Once the various subsections have been identified, there are several ways to optimize the power in each subsection:

• Shut down the complete subsection by switching off its regulator.

• Power down those peripherals that are not in use.

• Use the low-power modes of the microcontroller to reduce average power.

The most effective way to achieve low power is to switch off the regulator that is used to supply the power to the given subsection. If a particular subsection does not need to be available for a long period of time and the function it performs is not time critical, the regulator itself can be controlled using the host controller. A sensor is a good example of a subsystem that can be powered down when the system is not running. The only leakage current that will be consumed is the leakage in the regulator.

If the complete subsection can’t be powered down, then individual peripherals and components of the subsection should be looked into. For example, in the sensor section, there may be some sensors that need not be measured while others are being measured. Consider having a thermistor

Figure 1. High-level block diagram of a watch.

“Devices like Cypress’s

PSoC 4 have built-in analog

capability like analog-

to-digital converters.”

This protects the inputs of the receiver from

over- and undervoltage conditions, and from

overcurrent conditions. The output impedance

of the driver should be matched to the

impedance of the cable-trace so that there are

no reflections from the receiver side. Integrated

electrostatic discharge (ESD) protection also

helps to suppress the unwanted transients due

to overvoltage on the trace.On some logic devices, the inputs have input-

clamping diodes to VCC and to ground (GND)

(figure 5). The input-clamping diodes serve as

the overvoltage and ESD protection. When

using CMOS devices that have current-limiting

resistors at the inputs, the input voltage can

exceed maximum specified values as long as the

maximum current rating is observed.In some cases, especially in industrial and

automotive applications, the logic device may

need to interface with voltages far above the

normal 5V limit. In these cases, choose logic

devices with input-clamping diodes and use

3.6V, making them suitable for designs that use a

mix of 1.8 and 3.3V devices.When systems need unidirectional voltage

translation, shifting the voltage level from low to

high or from high to low, standard logic devices

are often a good choice for the function. Many

standard logic devices—equipped with features

like low-threshold inputs, open-drain outputs,

TTL inputs, input-clamping diodes, current-

limiting resistors, and overvoltage-tolerant

inputs—support one-way level shifting. As a

result, a mixed-voltage system can operate

without producing damaging current flow or

signal loss, and that can help increase efficiency

and save power.

V

RR

V=15V

Device A

15 V - (5.07 = 0.7 V)=

ESD protection

Clamping diodeInput buffer

I is found in the limiting values table of the datasheet.

I

Overvoltage-tolerant CMOS input

Input buffer

ESD protection

V =3V

Figure 5. Using current-limiting resistors to enable high-to-low level translation.

Figure 6. Diode-free ESD protection with an overvoltage-tolerant input.

current-limiting resistors. NXP’s LV, HC, and HEF

families have input-clamping diodes to VCC and

can be used with current-limiting resistors for

high-to-low level translation.DEVICES WITH OVERVOLTAGE-TOLERANT INPUTS

Newer ESD structures eliminate the diode to

VCC and use a grounded N-type metal-oxide-

semiconductor (NMOS) (figure 6). Without

the diode, any voltage within the limits of the

manufacturing process can be applied to the

input without opening a current path to VCC. As

a result, logic levels that exceed the device’s

power supply can be applied to the inputs

without impacting the application.Since devices with overvoltage-tolerant inputs

can tolerate a VIN higher than V

CC, and outputs

swing to VCC only, they make good choices for

high-to-low level translation. The NXP LVC, LVT,

ALVT, and AHC(T) families have inputs that are

overvoltage-tolerant to 5.5V, as long as input

and output current ratings are observed. The

inputs of AUP and AVC devices are tolerant to

AXP’s new, 30-page guide presents a number of techniques for managing mixed-voltage designs and gives detailed product recommendations. Click

here to download a copy of the guide. A complete listing

of all NXP’s voltage-level translators is available at

“When systems need unidirectional voltage translation, standard logic devices are often a good choice for the function.” FREE DOWNLOAD

www.nxp.com/logic.

September 2014

Interview with Umesh Mishra CTO of Transphorm

Unidirectional Voltage Translation

Designing Applications for Ultralow Power

Transphorm Redefines

POWER CONVERSION

Interview with Umesh Mishra Chairman and CTO of Transphorm

Given the emphasis on green initiatives, in which anything and everything is touted

as “energy efficient,” there’s been lots of chatter about low-power design. Naturally,

much attention is focused on switched-mode power supplies, power devices, and

power-conversion circuitry of all kinds. This is where a lot of power efficiency is

either lost or gained, depending on how carefully you approach the design task: a

milliohm here, a milliohm there, and pretty soon you’re talking about real voltage

drops that are going to affect the performance of a power-distribution system.

By David Maliniak

Technical Marketing Communication Specialist

Teledyne LeCroy

A Greener Test Bench with

Oscilloscope Software

POWERZero in on

ANALYSIS

TECH ARTICLEUsing Standard Logic Unidirectional Voltage Translation

TECH SERIESDesigning Embedded Apps for Ultralow PowerComplex Designs in Portable Devices

INDUSTRY INTERVIEWTransphorm Redefines Power Conversion Umesh Mishra, Chairman and CTO of Transphorm

TECH SERIESZero In on Power Analysis A Greener Test Bench with Oscilloscope Software

CONTENTS

3

High Current Power Line FilterThe RPC1299-30 is a dual stage DC power line filter designed to be used on high current applications, reaching up to 30 ADC. The device is suitable to be integrated on PCB circuitry and mounting due to its miniature size and space saving quality. The line filter operates at 75 VDC level and can withstand up to 2500 VDC hipot rating without compromising the state of its system. The RPC1299-30 functions well at a wide temperature range of -40ºC to +100ºC...Read More

3-Phase PWM Controller for VR12.5 CPUsThe ISL95821 is a three-phase PWM controller IC ideally designed for Intel VR12.5™ compliant microprocessor core power supplies. This device offers control and protection for a voltage regulator (VRs). The voltage regulator has integrated gate drivers and can be configured in 3, 2, or 1-phase. The voltage regulator utilizes a serial control bus to communicate with the CPU and attain lower cost and smaller board area.

The VR utilizes Intersil’s Robust Ripple Regulator R3 Technology™. The R3™ modulator has many advantages compared to traditional modulators, including faster transient response, variable switching frequency in response to load transients, and improved light load efficiency due to diode emulation mode with load-dependent low switching frequency...Read More

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Power efficiency is either lost or gained: a milliohm here, a milliohm there, and soon your talking about real voltage drops...Pg. 26

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TECH ARTICLE

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Power Developer

Many of today’s portable systems combine devices that work at different operating voltages.

Unidirectional voltage translators, which shift the voltage level up or down, can help these various devices work together more efficiently. Several families of standard logic include features that support level translation from low to high or from high to low.By Ali Zeeshan, NXP Semiconductors

USING STANDARD LOGICfor Unidirectional

Voltage Translation

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TECH ARTICLE

76

Power Developer

Today’s designers often have to work with devices that use different operating voltages. This is particularly true in portable applications, where the processor, the memories, and the peripherals are likely to require different supply voltages. In these situations, the output voltage level of a driver device needs to be shifted up or down so that the receiver device can interpret it correctly, or vice versa (figure 1).

Devices that translate voltages from low-to-high level or from high-to-low levels also transfer data. The data transfer can work in one direction (unidirectional) or in two directions (bidirectional). For our purposes, we’re going to look at unidirectional translation.

LOW-TO-HIGH LEVEL TRANSLATIONLogic devices equipped with low-threshold inputs or open-drain outputs can be used for low-to-high level translation.

Several standard logic families can be used for this purpose. For example, the NXP AHC(T) and HCT series operate in the 5V range and can be used to interface with 3.3V outputs. The NXP AUP1T and NX3 series operate in the 3.6V range and can be used to interface with 1.8V outputs.

In devices equipped with an open-drain output, the output can be pulled up to a voltage level matching the input requirements of the device it is driving. A pull-up resistor is used on the output for level translation (figure 3).

As an example, the NXP 74AUP1G07, a low-power buffer with an open-drain output, can be used to translate from 1.8 to 3.6V. Using an input and supply level of 1.8V, the open-drain output can be pulled up to 3.6V to drive the next stage with a VIH of 3.5V. Similarly, the NXP 74LVC1G07, a 3V buffer with an open-drain output can be used to translate from 3 to 5V. Using an input and supply voltage of 3V, the open-drain output can be pulled up to 5V.

One thing to keep in mind, though, is that using pull-up resistors with open-drain outputs causes the device to consume more quiescent current, as the external pull-up resistor consumes more power. Also, output rise and fall times depend on the value of the pull-up resistor used.

HIGH-TO-LOW LEVEL TRANSLATIONThis category includes devices with input-clamping diodes and current-limiting resistors, and devices with overvoltage-tolerant inputs.

When a driver is operating at a supply voltage higher than that of the receiver, the output voltage level of the driver must be lowered to match the input switching thresholds of the receiver (figure 4).

Driver T

1.8 V

1.8 V

1.8 V

3.3 V

3.3 V

3.3 V

Receiver

Receiver

Driver

ESD Protection

To Logic Circuit

GND

N1

P1

D1

VCC

P2

Figure 1. Shifting the output voltage level up or down.

Figure 2. Simplified CMOS input with lower-than-typical threshold values.

Input

GND

Pull-upResistor

(R)

V

Level shifterwith open-drain

output

Overvoltage-tolerant CMOS input

ESD protection

Input bufferOutput buffer

V =5V V =3V

Connector Cable

Figure 3. Open-drain output andpull-up resistor for level translation.

Figure 4. High-to-low level translation.

“NXP’s LV, HC, and HEF families have input-

clamping diodes that can be used for high-to-low

level translation.”

Complementary metal-oxide-semiconductor (CMOS) devices with input switching thresholds lower than the typical values can be used for low-to-high translation (figure 2).

The combination of N1 sizing and the drop across diode D1 determines the input threshold. Also, the P2 PMSO reduces crossbar current through the inverter.

98

TECH ARTICLE

98

Power Developer

This protects the inputs of the receiver from over- and undervoltage conditions, and from overcurrent conditions. The output impedance of the driver should be matched to the impedance of the cable-trace so that there are no reflections from the receiver side. Integrated electrostatic discharge (ESD) protection also helps to suppress the unwanted transients due to overvoltage on the trace.

On some logic devices, the inputs have input-clamping diodes to VCC and to ground (GND) (figure 5). The input-clamping diodes serve as the overvoltage and ESD protection. When using CMOS devices that have current-limiting resistors at the inputs, the input voltage can exceed maximum specified values as long as the maximum current rating is observed.

In some cases, especially in industrial and automotive applications, the logic device may need to interface with voltages far above the normal 5V limit. In these cases, choose logic devices with input-clamping diodes and use

3.6V, making them suitable for designs that use a mix of 1.8 and 3.3V devices.

When systems need unidirectional voltage translation, shifting the voltage level from low to high or from high to low, standard logic devices are often a good choice for the function. Many standard logic devices—equipped with features like low-threshold inputs, open-drain outputs, TTL inputs, input-clamping diodes, current-limiting resistors, and overvoltage-tolerant inputs—support one-way level shifting. As a result, a mixed-voltage system can operate without producing damaging current flow or signal loss, and that can help increase efficiency and save power.

V

R

R

V

=15V

Device A

15 V - (5.07 = 0.7 V)=

ESD protection

Clamping diode

Input buffer

I is found in the limiting values table of the datasheet.

I

Overvoltage-tolerant CMOS input

Input buffer

ESD protection

V =3V

Figure 5. Using current-limiting resistors to enable high-to-low level translation. Figure 6. Diode-free ESD protection with an overvoltage-tolerant input.

current-limiting resistors. NXP’s LV, HC, and HEF families have input-clamping diodes to VCC and can be used with current-limiting resistors for high-to-low level translation.

DEVICES WITH OVERVOLTAGE-TOLERANT INPUTSNewer ESD structures eliminate the diode to VCC and use a grounded N-type metal-oxide-semiconductor (NMOS) (figure 6). Without the diode, any voltage within the limits of the manufacturing process can be applied to the input without opening a current path to VCC. As a result, logic levels that exceed the device’s power supply can be applied to the inputs without impacting the application.

Since devices with overvoltage-tolerant inputs can tolerate a VIN higher than VCC, and outputs swing to VCC only, they make good choices for high-to-low level translation. The NXP LVC, LVT, ALVT, and AHC(T) families have inputs that are overvoltage-tolerant to 5.5V, as long as input and output current ratings are observed. The inputs of AUP and AVC devices are tolerant to

AXP’s new, 30-page guide presents a number of

techniques for managing mixed-voltage designs

and gives detailed product recommendations. Click

here to download a copy of the guide. A complete listing

of all NXP’s voltage-level translators is available at

“When systems need unidirectional voltage

translation, standard logic devices are often a good choice for the function.”

FREE DOWNLOAD

www.nxp.com/logic.

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1312

TECH SERIES

1312

Power Developer

Some portable systems can be fairly simple, and designing for ultralow-power use in one of

these system is not necessarily a great challenge. Larger systems, however, can be complex and a bit trickier. In this final installment of Designing

Embedded Applications for the Ultralow-Power, we will examine a larger system and explore

how to reduce average power consumption in light of design complexity.

By Sachin Gupta, Kannan Sadasivam Cypress Semiconductor

Part 3

Designing

ULTRALOW-forEmbedded Applications

POWER

To read the previous article in this series, click on the image above.

By Sachin Gupta, Kannan Sadasivam Cypress Semiconductor

Part 2

Designing

ULTRALOW-forEmbedded Applications

POWER

Generally, a system on a chip (SoC) supports more low-power modes compared to a traditional microcontroller unit (MCU). The reason for this is that due to the high level of integration, they have more

on-chip components, and multiple power profiles are needed to support different operating needs. The number of power modes and the resources available during each mode vary from device to device. For example, in a particular low-power mode, one device may power down everything and just retain register and RAM content while another may just power-down the central processing unit (CPU) while keeping other resources up and running. Different manufacturers may name these modes differently as well. For this article, we’ll cite the example of PSoC 4 devices from Cypress Semiconductor to explore power modes in detail.

To read the previous article in this series, click on the image above.

By Sachin Gupta, Kannan Sadasivam, Cypress

Part 1

Designing

ULTRALOW-forEmbedded Applications

POWER

Considering the importance of conservation, the portability of embedded systems is a key design consideration. Portable systems are generally battery-powered with

battery life dependent upon the systems’ power consumption. These days, as part of “Go Green” initiatives, power consumption is a selection criterion even for wall-powered applications.

Complex Designs in Portable Devices

1514

TECH SERIES

1514

Power Developer

Not all portable systems are as simple as those shown previously in this series of articles. Here,

figure 1 shows a typical block diagram for a wearable electronic device. The complexity of the design is magnified by presence of a multitude of functional blocks and subsystems.

A logical approach is to divide the whole system into various subsystems and analyze their power consumption individually. This can also help simplify design of the power supply domain in such a way as to enable low-power functionality.

The power in the display and touch controller section is dominated by the backlight drive and the display itself. Most designs utilize a timer-based time-out and power-down mode for the display. Typically, after some fixed time (T1) the backlight drops to a 50 percent duty cycle and is turned off after additional time (T2) when the display itself is turned off. At this point, even the touch controller could be turned off or put in a power-down mode based on the usage scenario. This would let the designer draw a current profile for this block and subsequently a typical current.

Antenna

Sensor Actuators

Touch Screen

Touch Screen Module Display Module

Display

Controller

Main Processor

LED Drive

Battery

BatteryCharger

PowerSupply withRegulators

WirelessController

SensorExcitation

Touch ScreenController

BackLightLEDs

Wireless controllers like those for Bluetooth are generally designed for low power. They have a way of duty cycling between high- and low-power modes. The typical numbers in the wireless controller’s datasheet are the best assumption we can make about power consumption without actually profiling a system. However, remember to take into account the duty cycling nature of these devices between the different power modes.

Sensor currents are dominated by the excitation current and the power consumed by the analog front end (AFE). Devices like Cypress’s PSoC 4 have built-in analog capability like analog-to-digital converters (ADCs) and other AFE components. This allows designers to dynamically power down these blocks through firmware commands. This level of control and granularity can further improve efficiency in low-power designs.

For complex designs involving multiple controllers and multiple modes of operation, it might make sense to also design the power-supply circuits to accommodate different controllable power domains. This allows a single controller on a standby power domain to actively control the other domains. This type of architecture could be expensive to design but very low in power consumption.

Once the various subsections have been identified, there are several ways to optimize the power in each subsection:

• Shut down the complete subsection by switching off its regulator.

• Power down those peripherals that are not in use.

• Use the low-power modes of the microcontroller to reduce average power.

The most effective way to achieve low power is to switch off the regulator that is used to supply the power to the given subsection. If a particular subsection does not need to be available for a long period of time and the function it performs is not time critical, the regulator itself can be controlled using the host controller. A sensor is a good example of a subsystem that can be powered down when the system is not running. The only leakage current that will be consumed is the leakage in the regulator.

If the complete subsection can’t be powered down, then individual peripherals and components of the subsection should be looked into. For example, in the sensor section, there may be some sensors that need not be measured while others are being measured. Consider having a thermistor

Figure 1. High-level block diagram of a watch.

“Devices like Cypress’s

PSoC 4 have built-in analog

capability like analog-

to-digital converters.”

1716

TECH SERIES

1716

Power Developer

Sachin Gupta has several years of experience in embedded solution development. He holds a bachelor’s degree in electronics and communications from Guru Gobind Singh Indraprastha University, Delhi. He can be reached at sachin@embeddedroots.com.

“Based on amount of radiation

allowed from the system, the pin can be set for a higher slew

rate or lower.”

“Consider having a

thermistor for temperature

measurement, one

accelerometer, and one

IR sensor.”

for temperature measurement, one accelerometer, and one IR sensor. The accelerometer may need to be checked quite often if there is movement and rest of the system needs to wake-up based on this. In contrast, the temperature sensor and IR sensor won’t be required most of the time. Now, let us consider the excitation for a thermistor (see figure 2). In this case, regardless of whether a measurement is being taken or not, there is current flowing through the thermistor and reference resistance.

Now, if the thermistor circuit is changed as shown in figure 3, this current can be avoided when the sensor is not being sampled. In this case, the pin is configured in strong output mode (CMOS inverter). Drive the pin low when the sensor output needs to be measured. This connects the themistor to Vss through a NMOS transistor. The only additional resistance that needs to be accounted for is the on resistance of the NMOS

Similarly, if the sensor subsection is implemented using a low-power mode that shuts down everything, the MCU can be woken up on a comparator interrupt when there is movement. The accelerometer output can be connected to the comparator, enabling the device to wake as soon as there is movement, triggering an event for the host processor.

With the systems that are built on SoCs, other techniques can be employed to reduce average power consumption. For example, all peripherals can be clocked using the slowest possible clock frequency, resulting in power savings since dynamic power consumption is directly proportional to the switching frequency. For example, ADCs in SoCs need to be clocked at a frequency that is generally proportional to the required sample rate. Setting up the ADC for a sample rate that is more than what is actually needed to meet system’s requirements will result in an unnecessary load on the batteries.

There can be other system level techniques that can be used to reduce

overall power consumption. For example, the output of the device can support a slower slew rate to reduce radiation. However, a slower slew rate causes FETs in the pin’s driver stage to draw more current as both PMOS and NMOS are on for a longer period of time. Based on amount of radiation allowed from the system, the pin can be set for a higher slew rate or lower.

Selecting a device that offers various power modes with significant integration and control over the SoC’s power state can simplify implementing a low-power system. Depending upon the application, various power modes can be used effectively to ensure low, average current. Though higher clock frequency results in high power consumption, running the CPU at a higher frequency and then putting the device into sleep sooner can yield a lower average power. Developers need to consider the whole system to ensure current leakage paths are avoided as much as possible.

Figure 2. Typical thermistor excitation circuit. Figure 3. Thermistor excitation for low-power consumption.

transistor, which tends to be very low. When the sensor output does not need to be measured, drive the pin high. This connects the thermistor to Vdd, resulting in zero current flow across the sensor circuit.

As the accelerometer does not need to be sampled all the time either, the ADC and other analog components like op amps or the reference generator used in the analog signal chain can be powered down when the signal does not need to be measured.

When this circuit is implemented using an SoC, there are various other ways to lower power consumption that will be discussed. If we consider the system shown in figure 1, the LCD controller can be put in hibernate mode and the host processor can wake it up by sensing an I2C command. When implemented using a PSoC 4, the power consumption can be as low as 20 nA.

Kannan Sadasivam is a Staff Applications Engineer with Cypress Semiconductor Corp. He has spent a considerable amount of his past career designing and integrating satellite subsystems. He loves working on different types of analog circuits and applications. He can be reached at qvs@cypress.com.

INDUSTRY INTERVIEW

2120

Power Developer

RedefinesEvery electron comes with a hidden cost. As power is switched and balanced to meet the demands of modern electrical systems and devices, countless terawatt hours are lost as heat. In fact, inefficient power conversion wastes tens of billions of dollars every year. As the need to reduce waste escalates, Transphorm, in Goleta, California, is working to meet the challenge and redefining power conversion. Leveraging modern materials and a talented research team, Transphorm’s ultraefficient power modules eliminate up to 50 percent of all electric conversion losses. From HVACs to hybrids, to servers, to solar panels, Transphorm enables significant energy savings across the grid.

EEWeb spoke with Umesh Mishra, Chairman and CTO of Transphorm, about today’s problems in power conversion, why gallium nitride (GaN) technology provides highly efficient solutions, and the challenges of working with GaN. Mishra also discussed the importance of research and development.

CONVERSIONPOWER

Transphorm

Interview with Umesh Mishra, Chairman and CTO of Transphorm

INDUSTRY INTERVIEW

2322

Power Developer

What led you to start Transphorm?

I cofounded Transphorm in 2007 with Primit Parikh with the purpose of applying gallium nitride (GaN) technology to the urgent and important problem of power conversion. We were lucky to have been funded by a series of exceptional financial institutions like, Kleiner Perkins, Lux Capital, Foundation Capital, Google Ventures, Soros Funds, INCJ, and more.

What differentiates Transphorm from its competitors that also use gallium nitride?

Our technical team, in my opinion, is the best in the industry. The team has incredible expertise with gallium nitride. We have over 17 PhDs at Transphorm, which reinforces our deep domain knowledge of the material. However, deep domain knowledge of GaN is simply not enough—we need production expertise and processes in place as well. Transphorm was recently ISO qualified, which is a huge achievement. We have processes in place for full data collection down to the growth of the gallium nitride material so that if there is any problem with the device, we have full traceability and can solve the problem.

Developing a disruptive new technology to serve as the new power conversion standard requires capital—and we are grateful to our investors for sticking with us and going through the growing pains of developing a robust technology. Transphorm’s culture is to be reliable and dependable, so we have always followed through on what we have said

we would do. We are not developing gallium nitride by rolling the dice—we have a methodology in place. We have full control over the supply chain. We understand the problems that can occur, so we solve them promptly. We are also ahead of the curve with GaN; other companies are saying that they are going to sample transistors now, but we sampled transistors over four years ago. There’s a big difference between sampling a transistor and it actually having the performance and reliability to survive in real-world applications. Transphorm is now the only company that has announced qualified products using 600V GaN technology, and our customers include marquee companies such as Yaskawa Electric and TATA Power. Lastly and very importantly, the breadth and depth of Transphorm’s technology has enabled it to have the strongest IP portfolio by far in GaN power, with over 450 independent patents and applications as well as more than 1,100 worldwide patents and applications overall. To develop any serious business involving a new technology, a strong IP portfolio is a must-have, and Transphorm has the dominant position.

What is the biggest problem in power conversion today?

Every time electricity is taken from the outlet, it is typically converted to another form of power for consumption. With every conversion there is loss, and when you add the total losses in the U.S. alone, it comes out to 300 terawatt hours. Part of that loss comes from larger applications like data centers, but it also occurs even in the laptop adapter we are all familiar with. To give you context on the significance of 300 terawatt hours, the entire western United States uses 230 terawatt hours annually. In particular, Las Vegas consumes 33 terawatt hours, and San Francisco uses 6 terawatt hours. Effectively, if you save 300 terawatt hours—which is what Transphorm aims to do—you can actually say that you are taking the western United States off the grid.

What is it about gallium nitride that makes it more fit for power conversion?

Gallium nitride is a very interesting material. It also happens to be the same material used in creating the LED light bulbs you can get from Home Depot. The reason that it produces blue light and that it can also be used for power conversion is its fundamental property: a very wide band-gap. Band gap is the property of the material that is measured in electron volts. Gallium nitride’s band gap is 3.4 electron volts, which indicates the amount of energy it takes to break the bond within the material. The larger the number, the more energy is needed to

We are not developing gallium nitride by rolling the dice; we have a methodology in place.Ga

N

INDUSTRY INTERVIEW

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GaN

The very wide band gap of gallium nitride allows it to be used for highly efficient power conversion.

Transphorm has the best gallium nitride team in the world.

break the bond. The more electron volts it has, the more volts it can hold, which is what power conversion requires—you have to be able to hold voltage in the “off” state and pass current in the “on” state.

At the heart of all power conversion is a switch. The properties of this switch are much like a mechanical switch. In the “on” state, it should not dissipate any power, and in the “off” state, you need to hold off voltage, which requires a large band gap. Gallium nitride easily meets these requirements. A mechanical switch is conductive because it has a metal-to-metal joint. In the case of gallium nitride, the electron mobility of the material is extremely high. In the high-mobility electron transistor from Transphorm, which is the manifestation of the gallium nitride material, the electron mobility is 2,200—an enormous amount compared to other competing power conversion materials like silicon or silicon carbide. In the “on” state, the high electron mobility leads to low resistance, and in the “off” state, the high breakdown field leads to its ability to drop voltage over a very small amount of material. The combination of these two makes GaN an exceptional switch for power conversion.

What are some of the challenges of working with gallium nitride?

We are a part of an industry that demands better performance at lower prices, which creates challenges at all levels. The first challenge is with the material. We had to figure out how to grow gallium nitride on a large substrate. Gallium nitride is grown on silicon so the standard economies of scale are applied to it. We had to learn how to grow GaN on silicon and do it well, which is a crucial part of our value proposition. Growing it well means you need to be able to do it over and over, while being stable and dependable in yielding device performance to prove that it is not a fluke and is scalable. In order to achieve this task, you need an exceptional materials science team. Transphorm has the best GaN team in the world, including materials.

The second big challenge is the processing of gallium nitride. We are not just experts in one part of the value chain at Transphorm, we know all aspects of it so that the final solution we serve to the customer is one that is optimized at all levels. Device processing is important because one of the things people have been talking about with gallium nitride is “dispersion,” which occurs when the resistance under switching operation of the device is higher than the DC resistance. This is due to imperfections—in both processing and growth—that show up as performance differences between DC and switching performance. Transphorm solved this problem in 2009, and other companies have recently announced progress on this problem.

Oddly enough, one of the challenges of GaN is that it is extremely fast. While GaN is being used in other applications like X-band radar and LTE transmitters, we are using it in power conversion, so you have to know how to harness the power of a device that is inherently very fast. In order to do this, we need to be able to have the ability to do radio frequency (RF) power conversion. Our team’s strong background in RF power and applications has been the basis for our success in the task.

Finally, you have to actually look at gallium nitride within the application. This means that you have to examine your final solution to determine whether or not it performs better than silicon; this is the ultimate test. Transphorm benchmarks GaN technology against the best silicon. We believe that the solution set that gallium nitride provides is game-changing for every situation in which power conversion exists.

The ability to have an exceptional team in each of these aspects— materials, devices, fabrications, packaging, circuits, applications— working hand-in-hand together has been critical to our success.

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Given the emphasis on green initiatives, in which anything and everything is touted

as “energy efficient,” there’s been lots of chatter about low-power design. Naturally,

much attention is focused on switched-mode power supplies, power devices, and

power-conversion circuitry of all kinds. This is where a lot of power efficiency is

either lost or gained, depending on how carefully you approach the design task: a

milliohm here, a milliohm there, and pretty soon you’re talking about real voltage

drops that are going to affect the performance of a power-distribution system.

By David MaliniakTechnical Marketing Communication Specialist

Teledyne LeCroy

A Greener Test Bench with Oscilloscope Software

POWERZero in on

ANALYSIS

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Likewise, control-loop analysis of such a circuit digs into variations in the parameters of a power supply’s feedback loop. For example, you might want to explore how well a pulse-width modulation (PWM) control loop responds to load changes. You can easily display the dynamics of the width variation on a per-cycle basis, and, for that matter, duty cycle as well.

“Better you should spend more of your time

getting results than setting up measurements.”

Figure 1. Teledyne LeCroy’s Power Analyzer software in action.

Thus, in all corners of the design and development infrastructure, there are efforts aimed at low-power

design. For one, device manufacturers are just as aware as you are of the critical nature of their products in determining overall system efficiencies. That’s why Intel has spent a fortune developing  22-nm FinFET 3D transistor technology for its next-generation processors. There’s tons of interest in gallium nitride (GaN) transistors for microwave power amplifiers because of their robustness at high temperatures. They’ll also fit well in applications like high-voltage switching devices for the power grid. Indium phosphide (InP) is another promising material for high-energy lasers and other high-power optical applications. Then there are the tools that design teams and technicians have to work with when facing the challenges of designing and debugging power supplies and associated circuitry. No designer or technician would dive into such a task without his or her trusty scope at the ready. Out of the box, most modern scopes will accomplish the basic tasks associated with power supply or device analysis, such as measurement of power losses, saturation voltages, high-side gate drive, dynamic on-resistance, and safe operating area. But setting up all

these measurements is a time-consuming task. Better you should spend more of your time getting results than setting up measurements. 

One way to reduce the overhead of power analysis is to equip your oscilloscope with power-analysis software, which serves to automate those measurements and analyses for characterizing power devices and circuits. Figure 1 is a screen capture from Teledyne LeCroy’s Power Analyzer software. The image is an example of device analysis, including analysis of power losses and safe operating area for the switching FET in a switched-mode power supply. Such software automatically sets up and displays a wide range of waveforms and parameters. In the example shown, the upper trace shows the field-effect transistor’s (FET’s) drain-to-source voltage while the center trace shows the FET’s drain current waveform. The bottom trace shows the power dissipated by the FET. Me hile, at right in the figure is a safe operating area plot with the horizontal axis being voltage and the vertical axis being current. The upper-right corner of the plot represents maximum power. Safe operating area (SOA) plots help determine whether the device is exceeding its maximum voltage, current, or power rating.

Low-power design is here to stay, and as system designs evolve to encompass more and more functionality, power analysis will be at the forefront of the battle to keep power consumption under control. If your test bench is on the front lines, then you probably ought to look into equipping your oscilloscope with power analysis software.

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