Three new LITTLE FOOT SO-8 power MOSFETs specifically intended for dc-to-dc conversion circuits in notebook computers were announced by TEMIC Semiconductors member Siliconix. Built on Siliconix's proprietary 32 million-cell TrenchFET technology, the new application-specific devices allow designers to obtain more efficient use of battery power without any increase in component count.

A Reduced Gate-Charge MOSFET With Faster Switching Speeds

The new Si4416DY has been optimized for notebook computer power conversion applications with faster switching speeds, lower gate charge, and the lowest on resistance ever achieved in a PWM-optimized device.

Turn-off times in the Si4416DY are more than twice as fast (32 ns) as the standard device typically used in these applications, while gate charge has been reduced by a third, to 24 nC. On-resistance is a low 18 milliohms at a 10-V gate drive. Since the Si4416DY runs 10% cooler than the standard solution, thermal design is also simplified.

"Bottom line, this part has the best combination of on-resistance and input capacitance/gate charge for notebook PCs, and it can be used with anybody's controller IC," said Phil Dunning, Product Marketing Director at Siliconix. "It can instantly replace products such as the Si4410DY with increased efficiency and no price increase."

Industry's First Dual-Gate MOSFETs Improve Light-Load Efficiency

The new Si4806DY (n-channel) and Si4807DY (p-channel) are the industry's first MOSFETs with two gate connections to maximize the efficiency of dc-to-dc converters that operate with two distinct load levels.

When the computer is operating in full-power mode, both gates are driven together to provide a maximum current rating of ý7.7 A. In light-load conditions, only the second gateýwhich controls a small part of the MOSFETýis driven, providing a maximum of ý2-A of current.

The availability of both n-channel and p channel versions supports several dc-to-dc converter topologies, including synchronous mode.

"There is a 50-fold difference between the level of current required by notebook computers in full-power mode versus sleep mode," said Siliconix's Dunning. "These new devices are the first power MOSFETs that operate efficiently at either end of that spectrum."

Designers previously needed to use two power MOSFETs, two dc-to-dc converters, or two switching frequencies to achieve the same level of power conversion efficiency. Not only do the new Si4806DY and Si4807DY save space compared to these solutions, they also avoid the EMI issues posed by multiple-frequency designs.

The Si4416DY is a neat combination of properties; looking for a device with the just the lowest on-resistance won't necessarily buy you the most efficient device, either in a generalized sense or in your specific design. The on-resistance here is low but is combined with a fast switching time and a really nice gate charge number which, in many cases, will simplify designs. But it is the other parts in this announcement that really get my attention:

The dual-gate parts make just so much sense that you have to wonder why it hasn't been done before! Obviously because no one had though of it. It makes absolute logic to provide what is effectively two devices in the same die, one device for the higher power, the other for the low power. Specifications at both the high and low current ends are good and the use of these two p-channel and n-channel devices will save a considerable number of components in applications where two separate current paths have been provided before; in applications where only a single current path has been provided, compromising efficiency at one use level or the other, there will be a massive leap in efficiency.

All three parts are in production and are, as noted, in the Little Foot SO-8 package. Pricing at 100,000-piece lot levels is $0.84 for the Si4416DY, $1.61 for the Si4806DY, and $1.68 for the Si4807DY.