Year to year, power MOSFETs don't change very much—a little faster, a little better on-resistance, nothing really radical. That sameness can also be said for susceptibility to cosmic rays. So it's surprising when International Rectifier announces a MOSFET breakthrough, and it's even more surprising when the story isn't about speed or losses but radiation hardness.
IR developed new n- and p-channel MOSFETs that switch with logic levels on their gates. They do a much better job than power bipolars in power converters for space applications. In commercial apps, that's not too exciting because there's a bandwidth overcapacity in the sky right now, just like on the ground. But for military apps, lots of new developments are possible (see "Chips In Space: On-The-Fly Intelligence," electronic design, August 23, p. 48).
Ordinary MOSFETs, whether they're power devices or CMOS-gate elements, are subject to single-event effects when exposed to cosmic rays. So, space-application power-supply engineers have used relatively low-efficiency bipolar transistors for switching. Besides not being terribly efficient, bipolars also require high base currents to ensure saturation. They need additional components to drive that base current from low-voltage logic gates as well.
Built on a new process technology, IR's IRHLUB770Z4 and IRHLUB7970Z4 can replace the venerable 2N2222A npn and 2N2907A pnp, which are still used because of their ruggedness in orbital and launch environments. IR won't say much about the process, except that it couldn't be reverse-engineered by examining the die. Also, the process has nothing to do with the package.
Electrically, the n-channel device turns on in 18 ns and off in 36 ns, and the p-channel device turns on in 44 ns and off in 54 ns. That turn-on is a little faster than the bipolars, while turn-off is six to nine times faster. However, the MOSFETs can switch 800 mA. Compared to the bipolars' 150, their switching losses are roughly 20 times lower, and conduction losses are lower by about half. On-resistance is 0.55 Ω for the n-channel and 1.2 Ω for the p-channel.
In terms of radiation hardness, both MOSFETs are characterized to 300 krad(Si) total ionizing dose (TID). They're single-event-effect (SEE) rated to a linear energy transfer (LET) spec of 82 MeV(Au).
The new power devices are available in a UB (3LCC) surface-mount or through-hole package. Pricing for the IRHLUB-7970Z4 and IRHLUB770Z4 begins at $80.00 each in 500-unit quantities.
International Rectifierwww.irf.com