EL SEGUNDO, Calif. April 2003 - International Rectifier, IR® (NYSE: IRF), today unveiled the first group of products in the family of DC Bus Converter Chip Sets that re-define the underlying distributed power architecture for 48V-input, 150W board-mounted power (BMP) converters used in telecom and networking systems.

IR's DC Bus Converter Chip Set architecture establishes benchmarks for overall efficiency, power density and simplicity, delivering more than 96% efficiency at 20A/150Wout in a circuit footprint less than 1.7in2. The Chip Set enables a 53% size reduction when compared to industry-standard quarter-brick form factors and slashes component count in isolated converters from approximately 50 components to 20.

The new Chip Set consists of a single IR2085S control IC and one pair each IRF7493 primary- and IRF6603 secondary-side HEXFET® power MOSFETs, plus the IRF7380 for primary-side bias and an IRF9956 for the secondary-side gate clamp. The Chip Set is designed for the isolated front-end of two-stage distributed power architectures (DPA) with an intermediate bus voltage feeding non-isolated point-of-load (POL) converters.

Two-stage DPA schemes do not require a tightly regulated intermediate bus voltage, since the POL will typically accept a relatively wide input voltage, and the POL provides the needed regulation to the load. In addition, multiple DC Bus Converter Chip Sets can be placed in parallel for higher power requirements.

"IR's DC Bus Converter Chip Set architecture removes the need for a regulated output at the intermediate stage, eliminating expensive feedback circuitry. Therefore, the overall solution is less complex, the component count is reduced and the board space needed for the conversion is smaller, while achieving over 96% efficiency," said Carl Smith, Marketing Manager for Networking and Telecommunication Products at International Rectifier.

Technical Highlights

The IR2085S control IC is the heart of the DC Bus Converter Chip Set architecture, and is based around a 50% fixed duty cycle, self-oscillating control scheme. The IR2085S replaces two SO-8 packaged devices, and is optimized for DPA applications. Features include an integrated soft-start capacitor that gradually increases duty cycle from zero to 50% for 5msec to limit in-rush current during start up, and maintains equal pulse widths for the high- and low-side MOSFETs throughout the start-up sequence.

The low- and high-side pulses for the half-bridge are matched to within ±25nsec to prevent transformer imbalances during operation. Other features include ±1A gate drive current optimized to work with IR's next generation low charge primary side MOSFETs, and includes adjustable dead-time from 50nsec to 200nsec to protect against shoot-through current. The deadtime can also be adjusted to limit the amount of body diode conduction on the secondary side, therefore maximizing efficiency.

The IR2085S has programmable switching frequency up to 500kHz for design flexibility. Higher switching frequency decreases output voltage ripple and allows use of smaller, lower loss magnetic components. Circuit designers can control switching frequency and deadtime independently with just two external components to customize circuits for their particular application.

A floating channel designed for bootstrap operation up to +100V DC and VCC supply under-voltage lockout is included. The IR2085S uses a new high voltage, high frequency level shift technology with high dv/dt immunity. The immunity is in the range of 50V/nsec to prevent unwanted turn on of the lower MOSFET in the half-bridge, and enables faster switching speed.

On the primary side, two 80V-rated IRF7493 MOSFETs in the SO-8 package are employed in a half-bridge configuration. It has low combined on-state resistance and gate charge, at 15mOhm(max) at 10V gate-to-source voltage, 31nC total gate charge and 12nC gate-to-drain charge for maximum switching performance.

On the secondary side, two 30V-rated IRF6603 MOSFETs in the DirectFET® package are used in a self-driven synchronous rectification topology. It has low on-state resistance and a thermally enhanced package, at 3.9mOhm(max) at 10V gate-to-source voltage, and 1°C/W thermal resistance to the PCB to deliver maximum current capability and efficiency.

IR's new architecture uses two biasing components. The IRF7380 dual 80V MOSFET has close threshold voltage matching and is used on the primary side in a novel biasing scheme. The IRF9956 secondary side dual MOSFET provides a gate clamp for the secondary-side synchronous rectification MOSFETs, clamping the drive voltage to 7.5V.

International Rectifier DC Bus Converter Chip Set

Part Number	Package	Voltage Rating(V)	RDS(on) max(mOhms)	Qg typ(nC)	Qgd typ(nC)	Function
IR2085S	SO-8	100V	-	-	-	Primary-side control IC, fixed 50% duty cycle, self-oscillating(1 per chip set)
IRF7493	SO-8	80V	15mOhms @ 10Vgs	31nC	12nC	Primary-side MOSFET used in half-bridge(2 per chip set)
IRF6603	DirectFET®	30V	3.9mOhms @ 10Vgs	39nC	17nC	Secondary-side MOSFET for self-driven sync rectification(2 per chip set)
IRF7380	Dual SO-8	80V	73mOhms @ 10Vgs	15nC	4.5nC	Primary-side MOSFET for primary-side bias(1 per chip set)
IRF9956	Dual SO-8	30V	100mOhms @ 10Vgs	6.9nC	1.8nC	Secondary-side MOSFET for gate clamp bias(1 per chip set)

For more information related to DirectFET MOSFET Packaging Technology visit the DirectFET Home page or the DirectFET Discovery Center

Pricing and Availability

The DC Bus Converter Chip Set samples and evaluation tools are available now. Production release for the chip set is June 2003. Pricing is US $7.67 for each chip set in 10,000-unit quantities.

High Resolution JPEGs are available in the Press Room.