El Segundo, Calif. - International Rectifier's new MOSFET-with-controller chip set, featuring four new high- efficiency DirectFET power devices designed to keep operating device temperatures and real estate requirements in tow, is optimized for primary-side and full-bridge DC/DC converter topologies. It's suited to applications that range from bulk 48-volt conversion for system boards up to 220 watts to powering 250-watt RF amplifiers in a base station system.
The company's IR2086S controller IC is designed for 36-75 volt isolated, primary-side full-bridge topologies. Designers choose from four DirectFETs—the 100-volt IRF6644 and IRF6655 and the 40-volt IRF6613 and IRF6614— to complete their chip-set solution.
The IR2086S full-bridge driver, working at 500 kHz, integrates self-oscillating circuitry (50 percent fixed duty cycle), a soft-start capacitor to limit inrush current, and hiccup current-limit protection that, with the DirectFETs, are designed to cut the number of external components by up to 60 percent and board space by half as compared to a typical quarter-brick design. The controller delivers a gate drive of ±1.2 amps; deadtime is adjustable (50 to 200 ns) to protect against shoot-through. The DirectFET devices, using the latest trench technology and MOSFET packaging, tout a dramatic reduction in on-resistance and gate-charge (QG): Typically 13 milliohms at Vgs = 10 and 33 nC for the IRF6644 (the first such 100-V DirectFET in an SO-8 outline); 60-milliohms and 8 nC for the IRF6655 (micro-8 outline with SO-8 performance, for low-current DC/DC converters); 3.4 milliohms and 42 nC for the IRF6613 (first 40-V part in medium size that replaces paralleled SO-8's); and 8.2 milliohms and 16 nC for the IRF6614 (micro-8 outline).
Applied to a typical telecom RF power amp, these chip set components (controller and four MOSFETs in a two-stage DC/DC configuration) can provide up to 250 watts at 28 volts and an operating efficiency greater than 95 percent. In this application, the first stage (using the IRF6644 sync FET and IR6655 control FET in a synchronous buck configuration) delivers a regulated output, with the second stage using the IR2086S and IRF6614 on the primary side and IRF6644 in the secondary. This solution, by virtue of operation at 50 percent duty cycle, allows lower voltage (100-V) MOSFETs in the secondary, boosting efficiency by up to 2 percent over what higher-rated (200-V) MOSFETs can provide, according to the company.
In networking applications (e.g., stand alone 48-V input bus converters), the IRF6644 can achieve nearly 96 percent efficiency at full load (27.5 volts at 8 amps). This solution provides 1 percent higher efficiency than circuits using single 100-V SO-8 MOSFETs, and more important, a 40°C reduction in device temperature. Thus this component eliminates the need to parallel additional devices on the primary side to handle higher current, and according to the company results in a 46 percent increase in output power from the IRF6644 solution as well as balanced temperature between the converter's primary and secondary sides. IR says the figure-of-merit in this application is improved by 45 percent.
The IR2086S is priced at $2.49, the IRF6644 at $1.10, 48 cents for the IRF6655, $1.47 for the IRF6613 and 64 cents for the IRF6614, all in 10k quantities.