Spurred primarily by current requirements of evolving voltage regulator module (VRM) specifications, inductor manufacturers are developing new designs that offer higher current ratings in conjunction with higher operating temperatures, lower direct current resistance (DCR), tighter tolerance and smaller package sizes.
Most inductor manufacturers agree that lower output voltages of microprocessors and multi-phase VRM designs are driving the need for high-current inductors. Now add higher operating temperatures, lower DCR, lower inductance values, and varying package and height requirements to the mix, along with new current sensing designs that require tighter tolerance, inductor manufacturers are faced with designing multiple product lines that provide the right tradeoffs for each application.
"The biggest single driver is the increased power of microprocessors in server and desktop PC applications," said John Gallagher, field applications engineer for power at Pulse, a Technitrol Company (San Diego, Calif.) To keep pace with Intel processor designs in PC and server applications, current load specs for VRMs have moved from 65 amps two years ago to 105 amps today and will move up to 150 amps over the next couple of years, he said.
Realizing there are tradeoffs in performance versus package size, inductor makers are offering a variety of inductor families to meet specific application needs. Many of them are meeting the challenge head on including CoEv Magnetics, J.W. Miller, Pulse and Vishay, which have introduced several new inductor products over the past six months to meet these changing requirements.
Here lies the challenge. As the switching speeds of processor chips increase, the voltage ratings are lowered, which automatically increase the amount of current, and this poses a very special challenge to inductor manufacturers particularly when they're trying to downsize the parts.
"Parts tend to get hotter as they are made smaller and if they're drawing more current as well it becomes more of an issue. Common materials, for example, start to age prematurely because of increased temperature, which can cause field failures," said Jim Holdahl, director of engineering, for Tyco Electronics, CoEv Magnetics (Watertown, S.D.).
To address the performance versus size dilemma in PC applications, CoEv Magnetics has designed new core shapes to maximize the inductor's performance in a minimum amount of space, and is working on new material developments.
As a result of its work in new core geometries, CoEv Magnetics plans to launch in the next quarter a new series, designated the DZM1306, for high-current applications. The new devices, available in a 13 mm x 13 mm x 7-mm package, offer a high current capability of over 20 amps, and an inductance range of 0.10 to 3.0 microhenries. The DCR rating ranges from 0.7 to 8.0 milliohms. They are rated for IR reflow at 280 degrees C, 10 seconds, and use a 200 degree C insulation system. The standard operating temperature range is -40 degrees C to 155 degrees C.
Designed for high efficiency applications, CoEv Magnetics recently introduced a new family of low voltage, high current inductors that provide a current handling capability of up to 30 amps for switching power supplies and portable electronics applications. The DXM series of lead-free inductors, available in a 13 mm x 13 mm x 6-mm package, offers an inductance range of 0.20 to 10 microhenries. The standard operating temperature range is -40 degrees C to 155 degrees C.
In addition, the DXM devices use a 200 degree C insulation system. The ferrite core material isn't susceptible to thermal aging, said the company, and provides a meantime between failure (MTBF) of greater than one million hours of operation.
"You're always fighting a bit of a tradeoff. The question is do you want to maximize power handling or maximize efficiency. The DZM offers maximum power and the DXM offers maximum efficiency," said Holdahl.
J.W. Miller has expanded its high-current, surface-mount power inductor series to include eight additional families that offer a wider range of sizes and values. These include the PM7232S, PM1038S, PM12639S, PM12645S, PM12651S, PM13560S, PM13656S, and PM13666S inductors in 7 mm, 10 mm, 12 mm and 13 mm footprints. These devices can be used in applications such as DC/DC converters in high-speed notebook and desktop computers, video game equipment, automotive, aerospace, telecommunications, RF/wireless and low profile, high-current power supplies.
The new J.W. Miller inductors offer an inductance range of 0.10 to 10 microhenries and can handle currents as high as 80 amps with a DC resistance as low as 0.54 milliohm. The device operates over a wide temperature range of -40 degrees C to 150 degrees C. Other key features include an operating frequency of up to 3 MHz and a very high saturation current to withstand high temperature applications.
Pulse has also boosted the current ratings of its surface-mount inductors with the introduction of its PG0084 series. Providing current ratings up to 32 amps, the low profile (4.0 mm), high power inductors are designed for AC/DC switched-mode power supplies and DC/DC converters in distributed power architectures (DPA), point of load (POL) systems and voltage regulator modules for servers, workstations, telecommunications switches, routers and base station equipment.
The new power inductor series features low DCR ratings from 0.90 to 9.0 milliohms, and a wide inductance range of 0.10 to 1.76 microhenries. In addition to six standard inductance values, custom inductance values are available. Saturation currents range from 16.5 to 58.0 amps. The series offers an extended operating temperature range of -40 degrees C to 130 degrees C.
Earlier this year, Pulse introduced a family of high efficiency, high frequency PA051X series of shielded inductors for multi-phase VRM applications that offer two times the energy storage density of comparable inductors, said the company. Packaged in a small 7 m x 7 mm x 5 mm package, the PA051X inductors are designed to meet size, efficiency and transient response requirements for server, workstation, desktop and portable computing applications.
Available in two platforms, the PA0511 and PA0512, they offer an inductance range of 72 to 220 nanohenries, a DCR value of less than or equal to 0.55 milliohm, and an operating temperature range of -40 degrees C to 130 degrees C.
In all these higher current applications, the inductance requirements are dropping because they need to deliver more power at a lower voltage than the processor, and respond to transient requirements, said Geoff Wildman, product line manager for the power products division at Pulse.
"Therefore, you need smaller inductance values, typically 200 nanohenries to 600 nanohenries, compared with two years ago when we were talking about 1 to 3 microhenries," Wildman said.
One of the newest design approaches in VRM or VR-D applications is using inductor sensing as a replacement for a current sensing resistor to determine how much current is being delivered at any given time.
Because the inductor's resistance is used to sense the current, it's driving the need for tighter tolerance for both DC resistance and inductance. In the past, +/-20 percent was sufficient but now there is a growing demand for +/-5 percent tolerance, Gallagher said. It's also driving the resistance down to .3 milliohm from about 1 milliohm a year ago, he said.
Pulse plans to introduce a new inductor for the VRM market in October to meet the tighter tolerance and lower DC resistance requirements. Designated the PA0513, the new device will offer a DC resistance of .3 milliohm and a tolerance of +/-7 percent.
Designed as a power and space-saving solution for automotive electronics, computers, servers, and telecommunications applications, Vishay Dale's IHLP-5050FD-01 surface-mount inductors are packaged in a small footprint of 12.9 mm x 13.2 mm x 6.5 mm for DC/DC converter and energy storage applications.
The high-current IHLP inductors offer an inductance range of 0.10 to 4.7 microhenries with a tolerance of +/-20 percent. The devices are rated for high saturation currents from 30 amps up to 120 amps, offer DCR values from 0.50 to 11.2 milliohms and exhibit low losses at frequencies up to 5 MHz. The operating temperature range is -55 degrees C to 125 degrees C.
The IHLP inductors feature an inductance drop of less than 20 percent at full rated current, which is a lower inductance roll off than provided by ferrite materials, said the company. The devices also feature a self-shielded package and meet military specifications for thermal shock, moisture, mechanical shock and vibration.
A few suppliers are also developing through-hole toroid inductors that meet high temperature requirements. J.W. Miller, for instance, recently introduced a new series of high temperature, toroid power inductors for high temperature applications such as automotive, military, aerospace, and petroleum industries. The through-hole 2100HT, 2200HT and 2300HT inductors offer an operating temperature range of -55 degrees C to 200 degrees C.
The new inductors offer an inductance range of 1.2 to 1000 microhenries with 38 amps maximum rated current. Custom ranges and current ratings are available. The inductors feature a self-shielding design, which emits a very low level of magnetic interference. Available in either horizontal or vertical mounting styles, the inductors are typically used in DC/DC converters, differential mode chocks, EMI filters and energy storage.
In addition to higher current ratings, there is a growing demand for higher temperature ratings. "Because they are packing more components in less space it generates a lot of heat in a confined area so the ambient temperature of the power supply will increase, and in these cases, the new toroids can handle the higher temperatures," said Andy Chow, senior engineer at J.W. Miller (Gardena, Calif.)
Pulse, a Technitrol Company
Tyco Electronics, CoEv Magnetics