Inductor makers, beseeched by data communications and telecom customers to weave improved performance characteristics into ever-tinier packages, are yielding impressive results. The smallest wirewound and chip inductors for high-frequency duty have shrunk to the EIA standard 0402 footprint, with smaller versions imminent. And performance is inching upward for chip inductors-which typically use thick- or thin-film construction techniques instead of copper wire windings and which lag their copper counterparts in such key parameters as Q, self-resonant frequency, tolerance and inductance.
Power chokes, serving largely in line filters, power supplies and dc-to-dc converters, are being forged into smaller form factors to follow shrinking motherboards. At the same time, vendors are advancing toward higher current capacity, efficiency and-thanks to advances in core materials-inductance values. And inductors increasingly are EMI-shielded.
When it comes to making demands on size and performance, cellular telephone makers are among the toughest customers. In the signal inductor arena, AVX Corp. (Myrtle Beach, S.C.) relies on a thin-film multilayer technology called Accu-L to produce 0805-size inductors between 1.2 nanohenries and 22 nH. Many can operate up to 2.4 GHz, well into the frequency ranges of emerging wireless communication services, and offer Q values between 40 and 60. Tight tolerances, another requirement for high-frequency operation, are met by the plus/minus 0.2-henry or plus/minus 2 percent precision available for most Accu-L parts.
Still smaller, with a 0402 footprint, are the newest CM10 signal inductors from Bourns Inc. (Riverside, Calif.) To compete with the performance of conventional wirewound inductors, CM10s are built on an alumina ceramic core that is coated with copper, which is then laser cut to produce a spiral winding. Within a few months the company plans to introduce an 0201 version, said Bourns project manager Bruce Alexander. In January the company will roll its CW20 and CW25 series of 1008-size inductors, similarly built but with an open construction to handle higher power.
Also targeting cellular phones is Murata Electronics North America Inc. (Smyrna, Ga.). The strategy, according to Gerry Hubers, product manager for EMI filters and chip inductors, is to downsize the chip components, offering tighter tolerances and lower profiles. Slated for release around midyear are thick- and thin-film units in the tiny 0201 footprint, with inductances from 1 to 33 nH. Devices in the 0402 footprint are also being planned for release next year.
Hubers disclosed that there will be new inductor offerings for use in voltage regulator modules and with electroluminescent driver ICs. Some laser-trimmable inductors are on tap. And important element of Murata's strategy is making chip inductor support tools available.
Associated Components Technology Inc. (Garden Grove, Calif.) is fielding the multilayer MIC0603 family, which extends to 33 microHenry and will shrink to an 0402 case during the first half, and the SMC0603, featuring self-resonant frequencies (SRFs) to 6 GHz. An earlier multilayer family, the SMC0805, also has minimum SRFs of 6 GHz, Qs as high as 56 and inductance values from 1.5 to 470 nH.
Other chip-size, thin-film signal inductors include three families from Vishay Intertechnology Inc. (Malverne, Pa.). IFC high-frequency chip inductors, aimed at wireless designs, use a proprietary photolithographic technique. Inductance values range from 1.5 to 18 nH for 0603s and from 1.5 to 47 nH for 0805s. Low-inductance parts in both sizes achieve SRFs of more than 15 GHz. Typical Q values are 50 and 37 at 1.7 GHz and 800 MHz, respectively, for 0603 inductors and 65 and 48 at 1.7 GHz and 800 MHz, respectively, for 0805s. The SIM-0204 family of metal-film-on-ceramic (mini-MELF) inductors, ranging from 1 to 100 nH, have minimum Qs of 32 to 50 and SRFs from 2 to 6 GHz. And Vishay's IMC-0402 inductors, built using laser spiral construction to achieve high Q and high SRF and to eliminate polarity in smaller values, reduce pick-and-place rework.
For top performance and highest inductance values at a given size, designers must turn to wirewound components, which today are being turned out in the tiniest of packages. In November, Coilcraft (Cary, Ill.) introduced its 21-member 0402CS series of inductors, measuring 0.047 by 0.025 inch and standing 0.024 inch high. Inductance values range from 1 to 40 nH. A 2.2-nH family member has a Q of 100 at 1.8 GHz, said to be twice that of the highest-Q non-wirewound version.
In October, NIC Components Corp. (Melville, N.Y.) added its NIN-H series of surface-mount wirewound inductors in 0805 and 1008 sizes, offering inductance of 3.3 nH to 4.7 microHenry and current ratings to 1 A. And earlier this year, Vishay unveiled it IMC-1008 series, sporting 1008 case sizes and ranging from 3.3 nH to 3.3 microHenry. Q ranges from 25 to 50 at high frequencies, dc resistance is as low as 60 milliohms and current ratings go to 600 milliohms.
Data line filters are the role cast for the 0.276 x 0.232-inch DR332 Dataline series, which Datatronics Romoland Inc. (Romoland, Calif.) announced in October. Intended for balanced data-transmission systems and such interfaces as RS-422, RS-423 and RS-48,5 as well as ISDN and CANbus lines, the 0.204-inch-high, wirewound inductive chokes come in seven values, from 5 to 4,700 microHenry, for filtering common-mode interference up to 10 kHz while passing signal frequencies up to 100 kHz. Subsequent versions of the DR series have expanded the inductance range down to 0.47 microHenry.
On the power side of the inductor world, wirewound construction reigns while the pressure to shrink package size for portable products is unrelenting. For those applications, Coilcraft introduced its nine-member DO1813HC family of power inductors in November. Standing 0.2 inch high in a 0.24 x 0.35-inch footprint, the inductors range from 0.56 to 48.1 microHenry and handle currents from 0.72 to 6 A. Dc resistance extends down to 10 milliohm.
For low-profile settings, such as PCMCIA cards, the company offers 0.047-inch-high LPO2506 surface mount power inductors, custom versions of which can knock the height down to 0.035 inch. The footprint is 0.3 x 0.35 inch, inductance ranges from 4.7 to 1,000 microHenry, and current ratings reach to 1.9 A. Where EMI is a concern, there's the self-shielded LPT1606 series. Standing 0.078 inch high and filling a 0.2 x 0.25-inch space, the toroidal components range from 1 to 22 nH.
Also introduced in November and aimed at reducing EMI is Vishay's LPT-3535 series of toroidal inductors, offering a choice of core materials. Units stand 0.235 inch high and 0.35 inch in diameter. Inductance values range from 1 to 330 microHenry. The 1-microHenry model with a powdered iron core and 4-milliohm resistance can handle up to 6.45 A. Two separate windings on each inductor allow series and parallel connections. Half- and quarter-height as well as custom versions are available.
For severe low-profile requirements, designers can turn to Vishay's ILS-3825 family of 0.047-inch-high, self-shielded, surface-mountable inductors ranging from 4.7 to 10 microHenry.
Vishay has added five high-current, surface-mount IDCP inductor families, in 1813, 2218, 3020, 3114 and 3722 packages, and six inductors in its IDC line, shielded or unshielded, in 2512-, 5020- and 7328-size packages.
Bourns has added two shielded, surface-mount power inductor series: the 0.12-inch-high SRR0603 and 0.18-inch-high SRR0604, each 0.26 inch on a side. Inductance is 3.3 to 1,000 microHenry; current extends to 1.8 A for the 0603 and 2.3 A for 0604.
Low-profile shielded inductors from Toko America Inc. (Mount Prospect, Ill.) include the D62CB and D63LCB, both filling a 0.12-inch-high, 0.25 x 0.24-inch footprint and ranging from 1 to 82 microHenry. Another shielded series, the 0.18-inch-high, 0.47 x 0.47-inch D124C, targets dc-dc converters for laptops and dc-ac inverter modules that power LCD backlights. The unshielded, 0.09-inch-high, 0.13 x 0.13-inch D32FU series, ranging from 0.33 to 3.3 millihenries, targets electroluminescent backlights.
This month, Cooper Electronics Technologies (Boca Raton, Fla.) announced the high-current surface-mount HC2 inductor family, using foil technology and aimed at the latest generation of microprocessors. Units offer low dc resistance and a frequency range up to 1 MHz. Also announced was a low-profile 0.4C version of Cooper's Uni-Pac surface-mount family; with values from 0.47 to 100 microHenry, it's suitable to 2 MHz.
Surface-mount power inductors from Associated Components Technology include the SPI-0804, -0810 and -1306, with respective maximum saturation currents of 9, 8 and 20 A; the SHS-0706, -1206 and -1208, with respective maximum currents of 5, 4 and 10 A; the 0.125-square-inch SPR series, with inductances from 1 to 10,000 microHenry and current to 3 A; the 0.44-square-inch SHR series, at 1 to 1,000 microHenry and up to 10 A; and the 0.078-square-inch E66, at 1 to 1,000 microHenry and up to 1 A.
CONTRIBUTING EDITOR GIL BASSAK CAN BE REACHED AT GLBASSAK@COMPUSERVE.COM.