audio/videoZONE Products for the week of October 2, 2007

International Rectifier Says…

IRS2092: Integrated And Protected Class-D Audio Chipset For High Performance
Flexible Chipset Can Scale From 50 - 500W by Simply Replacing MOSFETs

International Rectifier, IR, a world leader in power management technology, introduced a chipset featuring the new IRS2092 integrated audio driver IC with protected PWM switching and IR’s full complement of digital audio MOSFETs. The chipset targets medium power, high performance Class D audio amplifiers from 50W to 500W in home theatre, home stereo, active speaker, musical instrument, and professional audio applications.

“IR’s new chipset brings the audio efficiency and size advantages of Class D to high performance amplifiers, significantly shrinking the overall board area required by Class AB designs, without compromise to audio performance,” said Stephane Ernoux, marketing director for IR’s audio products. “Better still, the IC simplifies the designer’s job by delivering a flexible “building block” approach complete with protection, dead time, and PWM modulator which can easily scale to address changing design needs by simply replacing MOSFETs,” he added.

The new chipset forms a Class D audio solution that is much smaller than a comparable Class AB design. In a 100W application, for example, the IRS2092 IC and IRF6645 DirectFET MOSFETs reduce board size by 60% and eliminate 20% of the parts from the typical bill of materials.

EN-Genius Says…

The first Class-D amplifier I ever played with was the X-10, a 10-W amplifier from Sinclair Radionics. Clive Sinclair, now Sir Clive, was an entrepreneurial spirit, of whom it was said that he wasn't capable of banging a nail into a piece of wood. He later became very wealthy with the ZX80 computer,  which, for some time, met 50% of the UK's market needs. The X-10 was designed by Gordon Edge of the, now famed, Cambridge Consultants in 1964. He is now Professor Gordon Edge CBE. I bought my X-10 kit for the, at the time, outrageous sum of £5.19.6 (five Pounds, nineteen Shillings, and six Pence). Mine blew up at power-on, but those who successfully built the kit (you had to buy a mains power supply, prebuilt, for a separate £2.14.0) reported that the amplifier and the later, beefed-up, X-20 radiated like crazy.

Now there are many varieties of Class-D audio amplifier ICs, from mW for portable products to hundreds of watts for home theater and even professional use. Universally, the vendors promise higher efficiency for every watt of energy consumed from the supply voltage, or lower distortion per output watt -- or, sometimes, in a confused PR sort of way, both improvements. Some of the smaller power output devices also claim that the invidious EMI from a PWM circuit needs no output filter -- for their products -- if the speaker wires are less than X inches, or they use spread spectrum to bring the EMI within FCC limits. IR makes no such claims.

But no other vendor that I know of offers a scaling system for the audio output power, which is what International Rectifier is doing in this case. By scaling supply rails and output MOSFETs they are able to offer a range of solutions up to 500 W output power. Of course, IR is interested in selling MOSFETs; they make some damned good ones for all power work, with some very good ones for audio frequencies, but this combination is better than a sensible solution.

Programmable dead time protection for the MOSFETs is built into the IC (25 ns, 40 ns, 65 ns, and 105 ns) providing a tighter control of THD, while there is also programmable bidirectional over-current protection (up to 500 ns) with self-reset. Under-voltage lock out is provided. The inputs are floating to allow for simple half-bridge implementation using split rails -- up to ±100 V. On/off click noise suppression is embedded, while the PWM modulating frequency can be programmed as high as 800 kHz. The gate drivers can supply 1.0 A to the high side and 1.2 A to the low side. Dc offset is less than 20 mV.

Performance cannot be defined across the board because of all the possible configurations but the numbers look better than any I have seen elsewhere. Using an IR recommended circuit for a 50 W amplifier into 4 Ω, for example, the THD+N at 1 kHz is 0.01% while residual noise (with an AES-17 filter) is 200 µVrms. The IR reference design is a two-channel audio amplifier using IRS2092s and IRF6645 MOSFETs with channels rated at 60 W (into 4 Ω) each. No heatsinks are normally required and THD+N of 0.005% at 1 kHz at 96% efficiency in the power MOSFETs.

This scaling system allows a vendor to solve his audio output solutions with a single MOSFET driver, a single part to keep in inventory. The two output MOSFETs in a half-bridge format can be acquired from IR with voltage ratings up to 200 V and drain currents from 8.7 A to 65 A, allowing a real selection to suit your application today -- and total flexibility for that application tomorrow -- with 10 k piece prices ranging from $0.65 to $1.25. That real choice, that flexibility, and the performance specifications -- and the care taken over protection (Sir Clive!) -- make the IRS2092 a surefire, high volume, success story.

The IRS2092 is in production in Pb-free narrow SOIC-16 and PDIP-16 priced at $2.70 in 10-k piece lots. As noted, a reference design is available for 2 x 60 W channels.

Data Sheet