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Synchronous step-down controller with 95 percent efficiency

Posted: 21 Nov 2005 ?? ?Print Version ?Bookmark and Share

Keywords:Intersil? step-down controller? isl88550a?

Intersil Corp. expanded its power management portfolio with the introduction of a synchronous step-down controller with up to 95 percent efficiency. The new ISL88550A integrates a synchronous buck pulse width modulation (PWM) controller, a sourcing and sinking low dropout (LDO) regulator and a 10mA reference output buffer.

The PWM controller generates voltage for double data rate memory (VDDQ); the LDO regulator generates termination voltage supply (VTT); and the reference output buffer generates termination voltage reference (VTTR). With the combined features, the ISL88550A provides a complete solution for double data rate (DDR) I and II memory power supplies. It can also be used for other applications that require voltages down to 0.7V.

"The ISL88550A uses a constant-on-time PWM architecture with a programmable switching frequency of up to 600KHz, " explained Majid Kafi, director of Intersil's notebook power group. "This control feature handles wide input/output voltage ratios with ease and provides 100ns 'instant-on' response to load transients while maintaining high efficiency and a constant switching frequency that is ideal for DDR memory applications in desktops, notebooks and graphics cards. "

The ISL88550A drives two external N-Channel MOSFETs to generate output voltages down to 0.7V from a 2V to 25V input with output currents up to 20A. The LDO can sink or source up to 2.5A. Both the LDO output and the 10mA reference buffer output can be designed to track the REFIN voltage through a built-in resistive divider. This device also offers full programmable UVP/OVP and skip mode options that are suitable for portable applications. Skip mode allows for improved efficiency at lighter loads.

The VTT and VTTR outputs of the ISL88550A track within one percent of VREFIN/2. Intersil added that the high bandwidth of this LDO regulator allows excellent transient response without the need for bulky capacitors, thereby reducing overall system cost and size.

The ISL88550A is available in a 28-pin, 5-by-5mm thin QFN package and is priced at $2.85 in 1,000-unit quantities.

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