Synchronous step-down controller hits 95% efficiency

Intersil Corporation a world leader in the design and manufacture of high-performance analog solutions, today expanded its power management portfolio with the introduction of a synchronous step-down controller with up to 95 percent efficiency. The ISL88550A integrates a synchronous buck PWM (pulse width modulation) controller, a sourcing and sinking LDO (low dropout) regulator, and a 10mA reference output buffer.

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

“Intersil’s ISL88550A uses a constant-on-time PWM architecture with a programmable switching frequency of up to 600KHz,” said 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 well-suited 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. The high bandwidth of this LDO regulator allows excellent transient response without the need for bulky capacitors, thereby reducing overall system cost and size.

Key Features
* Constant-On-Time PWM with 100ns load-step response
* Start-up with pre-biased output voltage
* Up to 95 percent efficiency
* 2V to 25V input voltage range
* 1.8V/2.5V fixed or 0.7V to 3.5V adjustable output
* 200kHz / 300kHz / 450kHz / 600kHz switching frequencies
* Programmable current limit with foldback capability

Target Applications
* DDR I and DDR II memory power supplies
* Desktop computers
* Notebooks (including ultra-portable and Web tablets)
* Graphics cards
* Game consoles

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

To learn more, visit Intersil’s Power Management Web site at

More information on the ISL88550A is available at ISL88550A.

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