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Controller for bus converters allows greater than 95 percent efficiency

June 16, 2004 – Intersil today announced the release of the ISL6744, a double-ended controller intended for unregulated bus converters in 48-V DC-DC and off-line AC-DC power supplies.

The ISL6744 controller works over a wide range of input voltages, and works with isolated-bus applications including 400-V power-factor-corrected AC/DC converters and 48-V intermediate buses for telecom, datacom, and server systems. The intermediate bus architecture (IBA) provides voltage step-down conversion and high-voltage isolation to service many non-isolated point of load (POL) DC-to-DC converters.

In a typical 48-V IBA, the ISL6744 is used to translate the 48-V bus voltage down to a lower unregulated intermediate bus voltage, usually in the range of 8 to 16 V. This conversion circuit also provides electrical isolation, isolating the lower voltage bus from the 48-V bus in the event of catastrophic component failure. Non-isolated POL DC-to-DC converters then tap off of this low-voltage intermediate bus to provide even lower voltages directly at the distributed loads. In this way, the IB architecture minimizes wide-area distribution losses at the 48-V level, provides isolation for the intermediate levels and allows for the use of efficient and economical non-isolated POL regulators.

Keeping in mind that each level of conversion in an IBA or distributed architecture contributes to a cumulative reduction in system power conversion efficiency, all converters must have the highest possible efficiency. The ISL6744 has been designed to provide efficiency optimization with its ability to accurately program the output drive signals' non-overlap time with delays as fast as 20 ns – five to ten times faster than competing products. This performance allows power engineers to optimize the efficiency of their power modules and achieve conversion efficiencies greater than 95 percent.

In addition to high conversion efficiency, the ISL6744 provides an adjustable oscillator frequency, adjustable soft start, over-current shutdown, and precise control of the switching frequency. It features low start-up and operating currents, operation up to 1 MHz, integrated 20 V, 1 A MOSFET drivers, and very fast propagation delays, all in a tiny 8-lead MSOP or SOIC package.

For 48-V-input applications, the ISL6744 can be used to control the Intersil ISL6700 or HIP2100 MOSFET drivers to provide an efficient, robust and cost-effective solution. The ISL6744 is also designed to allow easy interfacing with low-cost gate drive transformers in AC-DC bus converter applications.

ISL6744 Technical Summary

  • Precision duty cycle and deadtime control to maximize efficiency
  • Up to 100 percent duty cycle operation for maximum efficiency
  • Adjustable delayed over-current shutdown and restart
  • Adjustable oscillator frequency up to 1 MHz to optimize efficiency and component costs
  • Adjustable soft start and over-current protection timing controls in-rush even for heavy loads
  • Adjustable soft start
  • 1-A MOSFET gate drivers for robust decisive switching and low-cost direct drive
    • Compatible with ISL6700 and HIP2100 MOSFET driver as well as other MOSFET driver solutions
  • Very low 100-A startup current
  • Internal over-temperature protection ensures reliability
  • Over-current protection ensures safe operation during current surges
  • Very short 35-ns control-to-output propagation delay
  • High integration offers minimal external component count
  • Input under-voltage protection
  • Small 8-lead MSOP and SOIC package options minimize board space

ISL6744 Pricing and Availability
The ISL6744 is available now. The suggested resale price for quantities of 1000 units is $1.30 for the ISL6744AU (MSOP package) and $1.20 for the ISL6744AB (SOIC package). Both packages are available on tape and reel.

The datasheet can be located here.

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