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KNOWLEDGE Chapter 3 By Steve Roberts Technical Director for RECOM
Understanding Datasheet Parameters RECOMÂ´s DC/DC Book of Knowledge is a detailed introduction to the various DC/DC converter topologies, feedback loops (analogue and digital), test and measurement, protection, filtering, safety, reliability, constant current drivers and DC/DC applications. The level is necessarily technical, but readable for engineers, designers and students.
Every respectable manufacturer supplies a technical datasheet with their product that details at the very least the basic operating parameters, overall dimensions and pin connections, but to compare one DC/DC converter with another just relying on the datasheet information often requires interpretation rather than just a simple comparison of numbers. The problem is that many of the specifications are inter-related so some parameter fixing is needed, i.e, that specific values such as the ambient temperature or input voltage are kept constant during the measurement of the performance specification of interest. For example, a load regulation figure will be made with nominal input voltage, 25°C ambient temperature and be valid over a specified load range. But there are no agreed standards between manufacturers over the parameter fixing, so some will specify a regulation value for the whole 0% – 100% load range, others for 10% - 100% and still others for 20% 80% load. This means a load regulation specification of ±5% for a load range of 10% – 100% is not necessarily worse than a rival converter with a load regulation specification of ±3% for a load range of 20% – 100%. Similarly a converter with a reliability specification of 1 million hours according to MIL-HDBK-217E is not necessarily more reliable than a
converter with a reliability specification of “only” 800 thousand hours according to MIL-HDBK-217F or another converter with “only” 400 thousand hours according to Bellcore/Telcordia. An unscrupulous manufacturer can use this lack of standardization to present their product in a better light. A classic example is the output ripple and noise specification, usually given in millivolts peak-to-peak (mVp-p). A converter with 50mVp-p is better than one with 100mVp-p, right? Well not if the fine print at the back of the datasheet states that the first converter measurement was made with a 47µF electrolytic in parallel with a 0.1µF MLCC across the output pins to additionally filter the output and the second converter specification was made without any external components. Additional filter components may be in some cases necessary in order to get a reliable, repeatable measurement, but the customer should be aware that the way the measurement is made affects the measured value and a comparison between two converter specifications can only be done if both are known. In many cases, it is necessary for the customer to measure the critical specifications of concern themselves using the actual or anticipated operating conditions of the application. For example, datasheets do not usually give efficiency versus operating temperature graphs (although RECOM can supply such detailed information on request).
TECH SERIES Measurement Methods: DC Characteristics
the validity of the datasheet, it is often worthwhile to use a measurement matrix where the various combinations of load and input voltage can be compared.
As already mentioned, the electrical behavior of a DC / DC converter is determined by many different parameters that are specified in the data sheet. To quickly and efficiently characterize a converter and check
Test Test VINVIN
Table 3.1 shows a typical a measurement matrix setup.
IOUT IOUT VOUT VOUT
1 1 VIN,NOM V I IOUT,NOM VO1VO1 VININ,NOM OUT,NOM IOUT VOUT 2 2 VIN,NOM VIN,NOM IOUT,MIN IOUT,MIN VO2VO2
VIN,MIN VV IN,MIN
VVO2 VO4 O4
OUT,NOM 3 3 VIN,NOM VIN,NOM IOUT,MAX IOUT,MAX VO3VO1 IN,NOM O3
24 4 35 5
IOUT,NOM IN,MIN IN,MIN IOUT,NOM
VVIN,NOM VVO3 VIN,MIN IIOUT,MIN IOUT,MIN VO5 OUT,MAX IN,MIN O5
VIN,MIN IIOUT,MAX IOUT,MAX VO6 4 6 6 VVIN,MIN VVO4 IN,MIN O6 OUT,NOM VIN,MAX IOUT,NOM IOUT,NOM VO7 IN,MAX O7 5 7 7 VVIN,MIN IOUT,MIN VVO5 VIN,MAX IOUT,MIN IOUT,MIN VO8VO8 IN,MAX 6 8 8 VVIN,MIN IOUT,MAX VO6
nominal nominal Input Input Voltage Voltage
minimum Input Voltage minimum Input Voltage nominal Input Voltage IN,NOM maximum Input Voltage maximum Input Voltage
minimum Input Voltage
maximum Input Voltage
nominal Output Current Output Current IOUT,NOM IOUT,NOM nominal
minimum Output Current* Output Current* IOUT,MIN IOUT,MIN minimum
nominal Output Current
OUT,NOM maximum Output Current maximum Output Current IOUT,MAX IOUT,MAX
minimum Output Current* IOUT,MIN Where Where â&#x20AC;&#x17E;I â&#x20AC;&#x17E;I â&#x20AC;&#x153; can â&#x20AC;&#x153; can be be â&#x2030;Ľ 0% â&#x2030;Ľ 0%
9 9 VIN,MAX VIN,MAX IOUT,MAX IOUT,MAX VO9VO9 Table 3.1: Measurement Matrix Table 3.1: Measurement Matrix
Table 3.1.9Measurement WhereVâ&#x20AC;&#x153;I VIN,MAX Matrix IOUT,MAX OUT, MIN â&#x20AC;? can be 0% O9
Â Â Â Â
Â Â Fig. 3.1: Measurement SetSet UpUp Fig. 3.1: Measurement
Where â&#x20AC;&#x17E;IOUT,MINâ&#x20AC;&#x153; can be â&#x2030;Ľ 0%
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Table 3.1: Measurement Matrix
maximum Output Current
To To obtain good and reliable measurement user should take a few basic obtain good and reliable measurement values, user should take a few basic thethe values, precautions on on how thethe measurements areare made. When preparing thethe testtest setset up,up, make precautions how measurements made. When preparing make
sure thatthat thethe contacts to the DC/DC converter have very lowlow resistance. Often measuring sure contacts to the DC/DC converter have very resistance. Often measuring terminals have variable contact resistances, so so thethe best testtest setup is ais"Kelvin" contact, terminals have variable contact resistances, best setup a "Kelvin" contact, as as shown above in Fig. 3.1, where current and thethe voltage paths areare connected shown above in Fig. 3.1, where the current and voltage paths connected Fig. 3.1: Measurement Setthe Up separately to to thethe pins. It isIt often tempting when using multimeters to to stack thethe 4mm separately pins. is often tempting when using multimeters stack 4mm Fig. 3.1. Measurement Set Up connectors in the meter sockets to connect up two or more meters, but this can lead connectors in the meter sockets to connect up two or more meters, but this can lead to basic To obtain good and reliable measurement values, the user should take a to few significant measurement errors. Each meter should be be separately connected to to thethe significant measurement errors. Each meter should separately connected precautions on how the measurements are made. When preparing the test set up, make converter pins as as shown above. converter pins shown above.
sure that the contacts to the DC/DC converter have very low resistance. Often measuring terminals have variable contact resistances, the best test can setup is aused, "Kelvin" To To load the DC/DC converter, power resistors orso power rheostats be be used, butbut it isit contact, load the DC/DC converter, power resistors or power rheostats can is as more shown above in Fig. 3.1, where the current and the voltage paths are connected elegant to use an an electronic load. However, some electronic loads need a minimum more elegant to use electronic load. However, some electronic loads need a minimum input voltage to regulate current properly, sowhen forfor converter voltages 4V,the input voltage topins. regulate the current properly, so converter output voltages below 4V, 4mm separately to the Ittheis often tempting using output multimeters tobelow stack often power resistors thethe only choice. Aup bench power supply makes a good often power resistors are only choice. A two bench power supply makes a can goodlead to connectors in the meterare sockets to connect or more meters, but this adjustable power supply, but make sure that it can deliver thethe necessary voltage and adjustable power supply, but make sure that it can deliver necessary voltage and to the significant measurement errors. Each meter should be separately connected current to cover all all of the input testtest requirements. It may be be necessary to combine several current to cover of the input requirements. It may necessary to combine several converter pins astoshown above. . The power supplies deliver V V . The power supplies to deliver current current limit limit must must be be setset so so that that there there is sufficient is sufficient IN,MAX IN,MAX
To obtain good and reliable measurement values, the user should take a few basic precautions on how the measurements are made. When preparing the test set up, make sure that the contacts to the DC/DC converter have very low resistance. Often measuring terminals have variable contact resistances, so the best test setup is a â&#x20AC;&#x153;Kelvinâ&#x20AC;? contact, as shown above in Fig. 3.1, where the current and the voltage paths are connected separately to the pins. It is often tempting when using multimeters to stack the 4mm connectors in the meter sockets to connect up two or more meters, but this can lead to significant measurement errors. Each meter should be separately connected to the converter pins as shown above. To load the DC/DC converter, power resistors or power rheostats can be used, but it is more elegant to use an electronic load. However, some electronic loads need a minimum input voltage to regulate the current properly, so for converter output voltages below 4V, often power resistors are the only choice. A bench power supply makes a good adjustable power supply, but make sure that it can deliver the necessary voltage and current to cover all of the input test requirements. It may be necessary to combine several power supplies to deliver VIN,MAX. The current limit must be set so that there is sufficient power to supply the DC/DC converter even at the lowest input voltage. Finally check the polarity before turning on â&#x20AC;&#x201D;the majority of DC/DC converters are not reverse polarity protected.
Measurement Methods: AC Characteristics Simply to take an oscilloscope, connect a standard probe to the converter and read the results off the display is not always reliable if the interference mechanisms and their interrelationships are not known. Differential mode (DM) and Common Mode (CM) effects can distort the readings. Section 5 describes DM and CM interference in more detail, but for now, it is sufficient to know that a simple oscilloscope probe largely ignores DM interference as it is symmetrical and occurs on both connections simultaneously, thus the DM component of the AC measurement is missing from the oscilloscope display. Another source of AC measurement error is the bandwidth capability of the oscilloscope. Oscilloscopes today have an input bandwidth of 400MHz or more. A closer study of the data sheet, however, reveals that the measurement of output ripple is typically carried out with a bandwidth limit of 20MHz. This is because on one hand the CM element beyond 20MHz is not so significant because it can be easily filtered out with a small capacitor and on the other hand the measurement should not be dependent on the type or manufacturer of the oscilloscope. An oscilloscope used without the 20MHz BW limitation option will always give higher readings.
od bo cb oc lio
F tF tt at ea
out a bandwidth limit of 20 This is because on oneripple handisthe CM element datawith sheet, however, reveals thatMHz. the measurement of output typically carried beyond 20MHz is not so significant because it can be easily filtered out with a small out with a bandwidth limit of 20 MHz. This is because on one hand the CM element TECH SERIES capacitor and onisthe other hand the measurement should not befiltered dependent on the type beyond 20MHz not so significant because it can be easily out with a small or manufacturer of the oscilloscope. An oscilloscope without the 20MHz BW capacitor and on the other hand the measurement shouldused not be dependent on the type imitation option will give higher An readings. or manufacturer of always the oscilloscope. oscilloscope used without the 20MHz BW
limitation option will always give higherPRACTICAL readings. TIP
Finally, the probe itself can be a source of error. Care must be taken that the cables to the Practical probe are as short as possible. Ideally, the tip of the probe touches to the + pin and the ground Tip Practical pin touches the ring. The use of the supplied earth clip must be absolutely avoided as the Finally, itself can be a source of error. Care must be taken that the cables to Tip the probe loop formed by the earth wire forms an aerial that picks up significant extraneous noise. the probe as short possible. Ideally, tipCare of themust probe to the pin and Finally, theare probe itselfas can be a source of the error. betouches taken that the +cables to the ground pin touches the ring. The use of the supplied earth clip must be absolutely the probe are as short as possible. Ideally, the tip of the probe touches to the + pin and avoided as pin the touches loop formed by the earth forms an aerial the ground the ring. The use wire of the supplied earththat clip picks must up be significant absolutely extraneous noise. avoided as the loop formed by the earth wire forms an aerial that picks up significant
Fig. way AC tosignals measure Fig. 3.2a:3.2a: WrongWrong way to measure
Fig. 3.2a: Wrong way to measure AC signals
Fig. 3.2b: Correct way to measure AC signals
Fig. wayACto measure Fig. 3.2b.3.2b: Correct Correct way to measure signals
AC signals 87
Power Developer Alternative AC Measurement Method If a probe with short contact paths cannot be used, then the proposal shown in Fig. 3.3 is useful. The impedance matching RC components avoid RF reflections that could interfere with the reading.
measured waveform is halved by the potential divider formed by the two ors, so the oscilloscope display should have Ă&#x2014;2 multiplication. Even with omponents, the coax cable should be kept as short as possible. Measuring Minimum and Maximum Duty Cycle
PRACTICAL TIP Note that the measured waveform is halved by the potential divider formed by the two 50-Ohm resistors, so the oscilloscope display should have 2x multiplication. Even with the matching components, the coax cable should be kept as short as possible.
ing Minimum and Maximum Duty Cycle
In some applications, it would be useful to know more about the internal modulation of a DC/DC converter, the duty cycle signal is often not directly accessible from outside the module. However, with some experience, an interpretation of the input or output noise can reveal this information.
ations, it would be useful to know more about the internal modulation of erter, the duty cycle signal is often not directly accessible from outside owever, with some experience, an interpretationTheofminimum the input orÎ´ output is duty cycle determined by the parameters V = al this information. MIN
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VIN,MAX and IOUT = IOUT,MIN, the maximum duty cycle Î´max by VIN = VIN,MIN and IOUT = IOUT,MAX. The period T is constant, because it is the operating frequency of the DC/DC converter. Fig. 3.4 shows how the duty cycle can be extracted from the input current waveform.
Output Voltage Accuracy The Output Voltage Accuracy characteristic, also called the Set Point Accuracy describes the specified tolerance of the output voltage. The parameter is usually specified in percent of the nominal output voltage, typically at room temperature, full load and nominal input voltage.
Measuring the the duty cycle the Output Waveform Fig. 3.4. Measuring duty cycle fromfrom the Output Waveform
duty cycle Î´MIN is determined by the parameters VIN = VIN,MAX and the maximum duty cycle Î´max by VIN = VIN,MIN and IOUT = IOUT,MAX. The stant, because it is the operating frequency of the DC/DC converter. Fig. the duty 10 cycle can be extracted from the input current waveform.
TECH SERIES Output voltage inaccuracy occurs because of component tolerances, especially in the resistor divider that drops the output voltage down to the reference voltage of the PWM comparator (refer back to Fig. 1.46). For output voltages higher than 1.5Vdc, it is common that a 1.22V bandgap voltage reference is used (a bandgap reference uses two PN junctions arranged so that the temperature coefficient of one junction cancels out that of the other to make a very stable reference voltage). For a 5V output voltage, the resistor divider will have a ratio of 3:1 so if 1% tolerance resistors are used, the output voltage accuracy will be Âą3%. In addition, the nearest standard value resistor may be used instead of the ideal value, so introducing another error. Some regulated converters have a trim capability, with which the output voltage can be adjusted within a certain range, typically Âą10%. In this case, this specification applies with the trim pin left open (unused).
Unregulated converters have an output voltage that is load dependent. If the nominal output voltage was set to be accurate at 100% load, then the output voltage would be higher than the nominal voltage for all loads below 100%, which could reduce the useable load range of the converter. Therefore, the output voltage is typically set to be accurate at around 60% - 80% load (refer to Fig 1.31). At full load the output voltage is thus always slightly below VNOM. So far, Chapter 3 of the DC/DC Book of Knowledge has covered the various types of measurement methods for both AC and DC characterstics. The chapter goes on to cover how to calculate efficiency in voltage conversion and an introduction to understanding thermal parameters. To read the chapter in its entirety, visit: http://www.recom-power.com/ http://www.recom-power.com/downloads/book-of-knowledge downloads/book-of-knowledge.
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By Josh Bishop
oday, we’re going to discuss electric vehicles, specifically electric cars. The crazy thing is that electric cars aren’t new; in fact, they were more popular than gas cars at the beginning of the 20th century. But, as cars became more popular, electric cars ran into the same problems that scientists and engineers are trying to overcome even today. Cheap and easily available gasoline as well as difficulties with range and ease of use all made gas vehicles come out on top. But now with modern technology, electric vehicles conceptually seem like a dream come true. Clean, quiet, efficient, peppy— what else could you want? However, the reality is much different. Until the Tesla, most electric cars were, well, pretty lame, small, and with relatively limited range. Besides this, a problem inherent in every electric car is that
while there’s no pollution at the source of usage, there is still energy consumed and pollution created in the production of both the car and the electricity. The electricity is pretty easy to track; if you live in Iceland where nearly all electricity is created by renewable sources, then the electricity has minimal environmental impact. If you live in China where the vast majority of the electricity comes from coal, then driving an electric car isn’t necessarily great for the environment. As to the production of the vehicle, it’s a lot harder to track where all the components come from but many parts, such as the batteries, are fairly toxic. I think that many people don’t understand the difficulty that engineers are working under when it comes to gas versus batteries. Gasoline has the specific energy of about 44-megajoulesper-kilogram compared to the typical
Some electric cars work with the smart grid to only charge when demand is low, like in the middle of the night.
electric car battery, lithium ion, which is somewhere between one half to three quarters of a megajoule per kilogram. Two orders of magnitude greater specific energy at the momentâ&#x20AC;&#x201D;thatâ&#x20AC;&#x2122;s a big gap to overcome. Also, battery lives are only a few years before needing to be replaced and very cold temperatures adversely affect them, reducing overall range. That range, which is expanding, still has to overcome the fact that gas and diesel distribution infrastructure is mature and robust, seeing that we have a gas station on nearly every corner. While charging stations have been cropping up, the time it takes to recharge the car and their relatively sparsity is a serious drawback.
But not everything is doom and gloom for electric cars. Environmental issues are being reduced where they can be, with some electric cars working with the smart grid to only charge when demand is low, like in the middle of the night. A lot of money is being put into the other concerns with electric cars. A huge amount of research is spent on making batteries and supercapacitors more energy dense and there is a lot of exploration into other types of energy storage such as flywheels and even compressed air. While the energy density difference is huge, electric vehicles also utilize the available energy more efficiently, so net energy usage
is less. And while Tesla has not had the smoothest start—nor have they sold as well as the Chevy Volt or Nissan Leaf—they show that sexy and electric can be used in the same sentence when talking about actual production cars. They’ve also been pouring insane amounts of money into making charging stations available and fast. Combine that with their unbelievable zero to sixty times in a family sedan with over two hundred mile range on their base model, they’re hard not to admire. Of course, since they’re so expensive, I’ll have to admire from a distance.
At the moment, it looks like electric cars will eventually became equal partners on the road with gas engines, even if they don’t replace them completely.
So, are electric cars the cars of the future? I don’t know. Maybe hydrogen will come from behind with its greater energy density. Or maybe there will be that decades awaited Mr. Fusion that takes care of all of our energy problems. At the moment, though, it looks like electric cars will, if nothing else, eventually became equal partners on the road with gas engines, even if they don’t replace them completely.
for External Power Supplies
THE GLOBAL REGULATORY ENVIRONMENT surrounding the legislation of external power supply efficiency and no-load power draw has rapidly evolved over the past decade since the California Energy Commission (CEC) implemented the first mandatory standard in 2004. With the publication of a new set of requirements by the United States Department of Energy (DOE) set to go into effect February 2016, the landscape is set to change again as regulators try to further reduce the amount of energy consumed by external power adapters.
Mandating higher average efficiencies in external power supplies has undoubtedly had a real impact on global power consumption. However, with the benefit of a reduced draw on the power grid come challenges and uncertainties for the electronics industry as it tries to keep up with this dynamic regulatory environment. Original Equipment Manufacturers (OEMs) who design external power supplies into their products must continue to monitor the latest regulations to ensure that they are in compliance in each region where their product is sold. The goal of this paper is to provide an up-to-date summary of the most current regulations worldwide.
A BRIEF HISTORY In the early ‘90s, it was estimated that there were more than one-billion external power supplies active in the United States alone. The efficiency of these power supplies, mainly utilizing linear technology, could be as low as 50% and still draw power when the application was turned off or not even connected to the power supply (referred to as “no-load” condition). Experts calculated that without efforts to increase efficiencies and reduce “noload” power consumption, external power supplies would account for around 30% of total energy consumption in less than 20 years. As early as 1992, the US Environmental Protection Agency (EPA) started a voluntary program to promote energy efficiency and reduce pollution, which eventually became the Energy Star program. However, it was not until 2004 that the first mandatory regulation dictating efficiency and noload power draw minimums was put in place. Figure 1 demonstrates just how dynamic the regulatory environment has been over the past decade. It also traces the path from the CEC’s 2004 regulation up to the new Level VI standards set to take effect February 2016.
Figure 1. The image above traces the path from the CECâ&#x20AC;&#x2122;s 2004 regulation up to the new Level VI standards set to take effect February 2016
THE CURRENT REGULATORY ENVIRONMENT As different countries and regions enact stricter requirements and move from voluntary to mandatory programs, it has become vital that OEMs continually track the most recent developments to ensure compliance and avoid costly delays or fines. While many countries are establishing voluntary programs harmonized to the international efficiency marking protocol system first established by Energy Star, the following countries and regions now have regulations in place mandating that all external power supplies shipped across their borders meet the specified efficiency level: Although the United States Department of Energy has established the more stringent Level VI standard, it is not set to go into effect until 2016. Today, Level V will meet or exceed the requirements of any governing body around the globe. Power supply manufacturers indicate compliance by placing a Roman Numeral V on the power supply label as specified
by the International Efficiency Marking Protocol for External Power Supplies Version 3.0, updated in September 2013. This latest version of the Protocol provides additional flexibility on where the marking may be placed. The European Union is currently the only governing body to enforce compliance to the Level V standard, though most external power supply manufactures have adjusted their product portfolios to meet these requirements. The adjustments are a direct response to the needs of OEMs to have a universal power supply platform for their products that ship globally.
Figure 2: The table above summarizes past and current performance thresholds as they were established over time. The term â&#x20AC;&#x153;powerâ&#x20AC;? means the power designated on the label of the power supply.
PERFORMANCE THRESHOLDS Figure 2 summarizes past and current performance thresholds as they were established over time. The internationally approved test method for determining efficiency has been published by the IEC as AS/NZS 4665 Part 1 and Part 2. The approach taken to establish an efficiency level is to measure the input and output power at four defined points: 25%, 50%, 75% and 100% of rated power output. Data for all four points are separately reported as well as an arithmetic average active efficiency across all four points.
CURRENT EXEMPTIONS Not all external power supplies are treated the same and exemptions exist in both the United States and the European Union.
In the US, Congress has written provisions into Section 301 of EISA 2007 that exclude some types of external power supplies. These are devices that: > Require Federal Food and Drug Administration listing and approval as a medical device in accordance with Section 513 of the Federal Food, Drug, and Cosmetic Act (21 U.S.C. 360c). > Power the charger of a detachable battery pack or charges the battery of a product that is fully or primarily motor operated. > Are made available as a service part or spare part by the manufacturer of an end-product that was produced before July 1, 2008 for which the external power supply was the primary load. Power supplies used for this purpose can be manufactured after July 1, 2008.
The European Union has instituted similar exemptions to the United States. External power supplies for medical devices, battery chargers, and service products are exempt. In addition, an exemption exists for low-voltage EPS devices. Low voltage external power supply means a unit with a nameplate output voltage of less than 6 volts and a nameplate output current greater than or equal to 550mA.
MOVING TO LEVEL VI Power supply manufactures, including
CUI, are already preparing for the coming transition to the more stringent Level VI standards. Along with tightened regulations for existing adapters, the new standard expands the range of products that fall under the standard. Regulated products will now include: > Multiple-voltage external power supplies > Products with power levels >250 watts The new performance thresholds are summarized in the following tables:
Single-Voltage External AC-DC Power Supply An external power supply that is designed to convert line voltage AC into lower-voltage DC output and is able to convert to only one DC output voltage at a time.
Low-Voltage External Power Supply An external power supply with a nameplate output voltage less than 6 volts and nameplate output current greater than or equal to 550 milliamps. Basic-voltage external power supply means an external power supply that is not a low-voltage power supply.
Single-Voltage External AC-AC Power Supply An external power supply that is designed to convert line voltage AC into lower-voltage AC output and is able to convert to only one AC output voltage at a time.
Multiple-Voltage External Power Supply An external power supply that is designed to convert line voltage ac input into more than one simultaneous lower-voltage output.
DIRECT VS INDIRECT OPERATION EPSs The new standard also defines power supplies as direct operation and indirect operation products. A direct operation product is an external power supply (EPS) that functions in its end product without the assistance of a battery. An indirect operation EPS is not a battery charger but cannot operate the end product without the assistance of a battery. The new standard only applies to direct operation external power supplies. Indirect operation models will still be governed by the limits as defined by EISA2007. Figure 3 illustrates the instructions provided by the DOE to help distinguish between direct and indirect operation power supplies:
LEVEL VI EXEMPTIONS The new Level VI mandate also defines exemptions for EPS products. The direct operation EPS standards do not apply if: > It is a device that requires Federal Food and Drug Administration listing and approval as a medical device in accordance with Section 360c of title 21; OR > A direct operation, ac-dc external power supply with nameplate output voltage less than 3 volts and nameplate output current greater than or equal to 1,000 milliamps that charges the battery of a product that is fully or primarily motor-operated.
Figure 3. The above instructions have been provided by the DOE to help distinguish between direct and indirect operation power supplies.
TECH REPORT LOOKING FORWARD
The compliance date for the new requirements has been set for February 10, 2016, two years after the rule’s publication in the Federal Register. It is important to note that compliance with the new standard will be regulated from the date of manufacture, so legacy products can still be shipped as long as the manufacture date is prior to February 10, 2016. Labeling requirements will be required to meet the same International Efficiency Marking Protocol for External Power Supplies Version 3.0 as the current Level V standard.
The EPA estimates that external power supply efficiency regulations implemented over the past decade have reduced energy consumption by 32-billion kilowatts, saving $2.5 billion annually and reducing CO2 emissions by more than 24-million tons per year. Moving beyond the mandated government regulations, many OEMs are now starting to demand “greener” power supplies as a way to differentiate their end-products, driving efficiencies continually higher and even pushing the implementation of control technologies that in some cases eliminates no-load power consumption altogether. In late 2014, CUI Inc began introducing Level VI compliant adapters to keep their customers one step ahead of the coming legislation. Moving forward, CUI will continue to look for ways to implement the latest energy saving technologies into their external power supplies in order to address market demands and comply with current and future regulations.
Globally, it is expected that other nations will soon follow suit with this standard. In the EU, the mandatory European Ecodesign Directive for external power supplies is currently going through revision discussions and it is expected to harmonize with most, if not all, of the US standards. It should be expected that countries with existing efficiency regulations in-line with the US, including Canada and Australia, will move to harmonize with the new standard as well.
View all Level V and Level VI compliant power supplies at:
www.cui.com/catalog/power/ac-dc-power-supplies/external www.cui.com/catalog/power/ac- dc-power-supplies/external
Protect Portable Electronic Systems
lthough we do our best to shield our portable devices from physical harm by using protective cases or by employing rugged design techniques, there is another layer of protection that can be applied. Within portable electronic devices themselves, load switches can be used to prevent damage from electrical surges, incorrect battery insertion, and other damaging events that can enter through the power source. Many systems such as smart phones, tablet computers, laptops, digital cameras, portable medical devices, industrial equipment, and other power-sensitive products already use load switches to provide robust protection against voltage and current surges. However, there are many variations and options available to designers and selecting the best match for an application can be a challenge.
Load Switch Basics Before selecting a load switch, let’s go over some basics of load switch functionality and performance. Basically, a high-side load switch connects or disconnects a power source to a load and the switch is controlled by an external enable signal (either analog or digital). High-side switches source current to a load, while low-side switches connect or disconnect the load to ground, thus sinking current from the load. The load switch circuits are active whenever the power is on and are thus designed to have low leakage currents. Furthermore, they must also have a low ON resistance to minimize their power dissipation when monitoring the system’s current or voltage.
At the heart of any load switch is a MOSFET (usually an enhancement mode device) that is either integrated into a load switch integrated circuit, or for higher power handling requirements, can be a discrete device. The MOSFET passes current from the power source to the load and is turned on or off via a control signal. Providing the control signal to the MOSFET, a gate-drive circuit connects to the MOSFET’s gate to switch the MOSFET on or off. Depending on the application, the gate-drive circuit can either be controlled by a wide variety of input voltages. This can receive either a low or high voltage digital signal and change the voltage to the intrinsic voltage communications level
Figure 1. A simple load switch typically consists of a MOSFET pass transistor that is controlled by a gate-driver circuit that level-shifts the input control signal to a value that will fully turn on the MOSFET, reducing the device’s ON resistance to its lowest possible level. (N-channel MOSFET circuit on the left, P-channel MOSFET circuit on the right).
TECH REPORT of the device. This function is also referred to as a level-shifting circuit since it has to generate a voltage high enough to fully turn on the MOSFET. Thus, a simple load switch will typically consist of a MOSFET pass transistor and a gate-drive circuit that contains a gate drive transistor and a few passive components (Figure 1). Such a circuit can be built using discrete components or integrated in IC form. N-channel MOSFETs have lower ON resistance values than P-channel devices, however to get the lower resistance values, a charge-pump circuit is needed to increase the drive voltage applied to the MOSFETâ&#x20AC;&#x2122;s gate.
The switches not only protect the systems, but they also help reduce power consumption by providing simple and efficient power distribution. Most of the integrated solutions include more functionality, providing multiple functions that work in tandem to protect the system. A typical load switch might contain circuit blocks to provide reverse voltage protection, reverse current protection, short circuit protection, output load discharge, overvoltage/overcurrent protection, over temperature protection, and some control logic to coordinate the various blocks (Figure 2). The switches not only protect the systems, but they also help reduce power consumption by providing simple and efficient power distribution.
Figure 2. A highly integrated version of the load switch will often provide multiple protection featuresâ&#x20AC;&#x201D; reverse voltage or reverse current protection, overvoltage/overcurrent protection, over-temperature protection and well as the integrated MOSFET and gate driver circuits.
The many possible applications for load switches let the manufacturers offer multiple configurations.
Several key parameters of a load switch are the ON resistance of the MOSFET that connects between the voltage input and voltage output pins, the current that the transistor can handle, and the voltage that the circuit can handle. The lower the ON resistance, the lower the power dissipation of the transistor and the lower the voltage drop from input to output. Today’s integrated MOSFETs typically have ON resistance values in the tens of milliohms, so, for example, if the load switch has an ON resistance of 50 milliohms and controls a 200mA load, the MOSFET dissipates just 2mW when ON, and has an input-to-output voltage drop of 10mV. Even a peak current of 1A would only cause a voltage drop of 50mV and peak power dissipation of 50mW.
Load Switch Options The many possible applications for load switches let the load-switch manufacturers offer multiple loadswitch configurations. A basic load switch such as the NX3P190 from NXP (Figure 3) resembles the circuit
Figure 3. A simple high-side load switch circuit from NXP, the NX3P190, integrates a P-channel MOSFET along with the level shifting and slew-rate control circuitry.
in Figure 1 right—it has the P-channel MOSFET controlled by a level-shifting and slew-rate control circuit. The MOSFET can support more than 500mA of continuous current with an ON resistance of 95 milliohms at a supply voltage of 1.8V. The voltage input, though, can handle voltages from 1.1 to 3.6V. Logic on the Enable input includes logic-level translation so that the switch can be controlled by lower-voltage microcontrollers and other circuits operating at reduced voltages. Targeted for power-domain isolation applications, it can help reduce power dissipation and extend the system’s battery life thanks to a low ground leakage current of only 2 microamps. A variation of the chip, the NX3P191 integrates an output discharge resistor that can discharge the output capacitance when the switch is turned off. This can prevent unwanted voltages from reaching the load. Another circuit from NXP, the NX3P1107, is functionally very similar, but the
TECH REPORT company reduced the MOSFET’s ON resistance by 2/3 to just 34 milliohms, thus allowing the chip to handle up to 1.5A of continuous current. That higher current rating allows the chip to tackle heavier load applications such as battery charging, digital cameras, smartphones, and many other applications. For applications that don’t require the high current but need the output discharge capability, another version of the chip, the NX3P2902B, can handle 500mA of continuous current and has typical ON resistance of 95 milliohms.
The chip can handle a continuous current of 1A, and has an ON-resistance of 100 milliohms, maximum, at a supply voltage of 4.0V. The power supply input pin can handle levels from 3 to 5.5V, but the VBUS input can tolerate as much as 30V. In a typical application, the USB OTG voltage source and control circuits connect to the chip’s voltage and control inputs, and the chip delivers a clean USB power and data output. A slightly higher power version of the chip, the NX5P2090 can handle 2A of continuous current.
Taking aim at more complex system applications such as USB on-thego (OTG) power management, the NX5P1000, an N-channel device in this case, includes under voltage protection, over voltage lockout, over-current, over-temperature, reverse bias, and in-rush current protection circuits (Figure 4). These circuits are designed to automatically isolate the VBUS OTG voltage source from a VBUS interface pin when a fault condition occurs.
Depending on the load current required for your application, as well as the level of protection you need, you have a wide choice of design options to get the best fit for your application. The devices discussed in this article represent the two extremes—the simplest integrated option and one of the most complex integrated solutions. There are, of course, many solutions in-between the two offered by NXP and other vendors.
Figure 4. Designed to support the USB on-the-go interface, the NX5P1000 integrates an N-channel MOSFET and includes voltage, current and temperature protection functions as well as electrostatic protection on the USB data, ID, and VBUS lines.
ZAMC4100 Actuator and Motor Controller From
The ZAMC4100 actuator and motor controller is an integrated, single package solution. With rich diagnostic features and optimized thermal performance and LIN bus interface, the ZAMC4100 is well suited for automotive applications like high-end mirror controls, as seen in the evaluation kit supplied by ZMDI.
• Evaluation kit with a test mirror • 9mm by 9mm 64-pin QFN package • Exposed pad for thermal management • Minimal external components in normal usage • Easy to setup • Half bridges are connected to motor drivers • High side load switches for the heater • Other high side switches for other higher power lights. • Easy-to-use GUI interface
The ZAMC4100 can be used in a variety of settings, from automotive, to home, medical, industrial, and even security systems. Wherever you need intelligence and motor control in a very small package, the ZAMC4100 is an ideal candidate. For more information, please visithttp://www.zmdi.com zmdi.com.
Tech Specs The ZAMC4100 is an integrated single package solution that features an ARM Cortex-M0 microcontroller and several peripherals that make motor and actuator control easy. With four integrated half-bridge drivers and four high side load switches, the ZAMC4100 can control multiple motors or other loads at the same time, perfect for small, yet relatively complicated scenarios. Ideally suited for the automotive industry, this also has a LIN bus interface, a wide six to eighteen volt working range with over and undervoltage protection, and a specific output buffer for programmable electrochromatic mirror controls, using a 6-bit DAC. With built-in thermal protection, the ZAMC4100 will shut itself down before excess heat can cause lasting damage.
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Keeping leakage current low ensures that even if a person is in the conduction path for the leakage current, it wonâ&#x20AC;&#x2122;t be harmful. Mean Well medical power supplies are designed to have point one milliamp to point three milliamps leakage current, compared with one milliamp and above for typical power supplies. This is well below the levels at which people will feel the current flow and makes the devices very unlikely to cause harm. In addition to leakage current, the International Electric Code requires supplies to have some means of protection or M-O-P. There are two important M-O-P ratings relating to power supplies, means of operator protection, M-O-O-P, and means of patient protection, or M-O-P-P. Every medical supply must fall into one of the four categories in the International Electric Code. Each category will determine where the medical supply can be used, for example in the patient vicinity, where the requirements are more stringent or in the operator
vicinity such as lab away from patients, which is less stringent. All Mean Well medical supplies are designed to be at least one M-O-O-P while most are two M-O-P-P, which is the highest level. Mean Well has an enclosed type series, the MSP series under M-O-O-P, and an open frame series, the RPS series under two M-O-P-P. They both have a no-load power consumption of less than three quarters of a watt and the RPS series is suitable for type B-F applications, as long as the final product is appropriate for type B-F. Mean Wellâ&#x20AC;&#x2122;s GSM product line features two M-O-P-P, an Energy Efficiency Level Six, and a no load power consumption of less than .1 watt. They are also certified by the International Electric Codeâ&#x20AC;&#x2122;s requirements for home health care usage. There are a variety of options as the GSM line includes eighteen watt to thirty-six watt wall mount medical adaptors and forty to one hundred twenty watt desktop adapters. To view this product video, click here here.
For more information on how Mean Well can address your medical power supply needs, and for other power supply products, please visithttp://www.meanwell.com www.meanwell.com.
Simple POWER ICs Deliver Unparalleled
Complexity Interview with Jon Cronk Product Line Director at Exar
Exar’s Universal PMICs Offer High-Density, Efficient, and Intelligent Programmable Power Power supplies have come a long way in the past few decades. In the early ‘90s, simplicity in power supplies meant that the supply was up and running, performing tasks as expected. Recent developments in power management IC technology have led to a re-definition of “simplicity.” Exar, a leading power IC company, has developed a line of universal PMICs that allow for high complexity operations, while simultaneously simplifying the rest of the system. In addition to powering the system, the PMICs provide high-density, efficient, and intelligent power management—all of which address the most critical driving forces in the market today. EEWeb spoke with Jon Cronk, Product Line Director at Exar, about the company’s line of universal PMICs, how they differentiate themselves in the power market, and some of the unique applications they have been working on with their clients.
What exactly is Exar doing in power and power management?
The main driving forces we see are: simplicity, density, efficient low power modes and intelligence...
Exar took a look at the main driving forces in the market today. We can talk about trends in the market place, however, “trends” like the proliferation of rails as a result of Moore’s Law is not a trend, because it is not necessarily a new development. The main driving forces we see are: simplicity, density, efficient low power modes and intelligence, which is comprised of telemetry and monitoring, dynamic control and reconfigurability of the power system. In the density and simplicity areas, Exar has released five power modules to address these trends— two of those fall under our universal PMIC family of programmable power devices, which are the XRP9710 and XRP9711. We have also released three power modules that use a proprietary constant, on-time control scheme, which XR79110, XR79115 and XR79120, which are 10A, 15A and 20A modules, respectively. These modules address density in a number of ways. The first is the 10A, 15A and 20A parts are the smallest in the market place minimizing board area. They are also simple because they are modules, meaning they take a lot of decisions away from the designer, so they simply have to fix the output voltage and make a few other adjustments— they don’t have to source MOSFETs or inductors. By implementing a QFN technology the way that we have, we make manufacturing a lot easier. Unlike some of the popular LGA modules in the market, these are easier to assemble,
they have better thermal performance because junction-to-case temperature is improved through a large copper area on the bottom, and all electrical nodes are available at the edges of the module so there are no hidden nodes in the debugging process.
How can simplicity address complex power systems? Simplicity can have other meanings as well. In the early ‘90s, simplicity meant getting a power supply up and running. Nowadays, simplicity can be applied to complex systems; for instance, one may have some sophisticated sequencing and timing and fault reporting that your system needs. That is where our universal PMICs step in. The simplicity comes from design tools to get the power system up and running to then quickly being able to integrate it into the rest of the system. Consider the sequencing requirements of an FPGA that hasn’t released yet and you have to get a power system figured out, our universal PMICs make it very simple for the customer to quickly modify the power system in order to meet the needs of an FPGA before it is available to be put on the board. We recently helped a customer on a simplicity issue that is worth sharing. The customer had about 40,000 networking systems deployed and they added another line card to the system. When the systems in the field powered up with the new line card, it caused an overvoltage fault condition on one
INDUSTRY INTERVIEW of the outputs causing the outputs to shut down. The customer at the time was using our XRP7714 universal PMIC with programmable power technology. They were trying to figure out the cause of the fault and if it causes a real issue. They determined that the overvoltage transient did not pose a problem in the overall system. They needed to turn off the overvoltage fault protection in the part and they could get a working system again. If they were using an analog controller of any type, an overvoltage is an internal function of the chip and
the customer could be stuck with that problem. In this particular case, we were able to guide the customer to change a single bit in the configuration of the part in the nonvolatile memory from a 0 to a 1 and disabled the overvoltage protection. The result was that they were able to do a software push out to their systems and eliminate all of these failures overnight without sending a single technician out into the field. That is one of the strongest features of the simplicity inherent in our universal PMICs. Not from the digital control loop that is the focus of so many.
PMICs make it very simple for the customer to quickly modify the power system in order to meet the needs of an FPGA before it is available to be put on the board.
In terms of digital power and programmable power, what are some of the main differentiating factors of Exar’s solutions?
Exar has been working on programmable power devices for over a decade now.
Dynamic voltage control and programmability comes in all digital controller offerings. However, some of the things that differentiate Exar are that almost everybody else out there is doing their digital control with an ARM, in a PIC or DSP core running code. Those options consume huge amounts of power even when sitting there doing nothing. There is 20mA to 30mA/output on a digital switching controller, which is normal and Exar does that with no more than 2mA/ output, which is a significant reduction in power consumption. We do that because instead of using a processor running code, we run a state machine which reduces
Our PMICs are used in everything from teleconferencing systems to IP cameras to high-end audio systems to military applications.
our cost, ensures that we get it right up front and reduces the quiescent current by an order of magnitude. Exar has been working on programmable power devices for over a decade now. Our first part was released in 2009 and the latest parts were released in the last part of last year. We use the term “universal PMIC” as tongue-andcheek, because PMICs are dedicated to a particular processor. Unfortunately, all processors don’t go into the same dedicated system in customer platforms. Our universal PMICs are as marketspecific as an FPGA, meaning that it can be used for any kind of embedded system that you could possibly think of. I would argue that our universal PMICs are more widespread in the broader market than any other in the market
INDUSTRY INTERVIEW today. Our PMICs are used in everything from teleconferencing systems to IP cameras to high-end audio systems to military applications. We are in a broad range of applications, which drove us to our last product release in November of last year—the XR77129—which is the only digital control loop, programmable part in the marketplace that has a 40V input voltage range. That was at the request of our broad industrial customer base.
What are some efficiency specifications of the universal PMICs? Our universal PMICs have the lowest power consumption in the market today. Low power and light load modes are the one of the driving forces in the market. Right now, we don’t participate in the mobile device market where quiescent
currents are in the microamp range. We have a few products and the IP to address it when we deem appropriate. But, if you take a look at our universal PMICs, we are the only ones that have a digital PFM mode, which reduces power consumption at light loads in power supplies to reduce switching losses. If you were to do that for a four-output switching controller that consumed 20mA to 30mA/output in a digital controller, having a light load mode doesn’t do much because it consumes around 120mA. If you look at our XRP7724 or the 40V follow-on, the XR77129— when all four outputs are in PFM mode you are consuming around 3.5mA for the entire system. With this, you can maintain efficiencies in excess of 80% all the way down to load currents as light as 10mA on a 20A rail. Exar’s solutions offer the best efficiencies at light loads by far.
Is power management something that a lot of power engineers struggle with? It is variable. You can come across a small company that has one person doing the entire hardware system that, in general, would not be power-savvy. With larger customers like Intel who are highly skilled in power, they chose Exar’s XRP7724 to power the system rails on their Intel Grantley platform. The universal PMIC powers 11 rails in the new server platform that follows Grantley. The reason for that is as these systems become more sophisticated in their power management and the desire to monitor the different outputs and their status, we provide the best trade-off between cost and telemetry that is available today. We also have an extremely low component count
If your power system can’t be touched by your software system then that piece of hardware on your board does not allow you to differentiate your product.
when compared to other digital or analog solutions with digital wrappers on them.
In the marketplace, there is a lot of talk about the IoT and wearables, which all require unique power solutions—what do you see as the next exciting movement in power? Power systems of the past were to do two things: provide power and be as small as it could. However, on the intelligence side, with our universal PMICs and other similar programmable products, we now have a power system that can be touched by the software engineer. If your power system can’t be touched by your software system then that piece of hardware on your board does not allow you to differentiate your product. With a dynamic system, you now have the capability to differentiate.
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