48-V constant on-time synchronous step-down converter

Texas Instruments Incorporated introduced three 48-V synchronous buck regulators with integrated high-side and low-side MOSFETs for single- and multi-output power supplies. The 650-mA LM25017, 300-mA LM25018 and 100-mA LM25019 Fly-Buck™ converters feature constant on-time (COT) control architecture that reduces board space by up to 40 percent when compared with traditional designs that require multiple DC-DC converters.

Typical application schematic

Constant-On-Time (COT) control scheme is one  in which the on-time is terminated by an on-timer, and the off-time is terminated by the feedback voltage (VFB) falling below the reference voltage (VREF). Therefore, for stable operation, the feedback voltage must decrease monotonically, in phase with the inductor current during the off-time. Furthermore, this change in feedback voltage (VFB) during off-time must be large enough to suppress any noise component present at the feedback node.

The LM25017, LM25018 and LM25019 enable non-isolated voltage regulators and multi-output solutions from input voltages as high as 48 V. Pin-compatible LLP and PSOP packaging offers a scalable solution that covers a wide range of power requirements. Each Fly-Buck converter can be configured to provide positive and negative voltage rails, or isolated multiple outputs with excellent cross-regulation.

12 to 48V input, 10V @ 500 mA output buck converter design

Typical isolated application schematic

The Fly-Buck converters are pin-to-pin compatible with TI’s 100-V, 600-mA LM5017, 300-mA LM5018 and 100-mA LM5019 wide input voltage range regulator family.

Key features and benefits of the Fly-Buck converters

• Fly-Buck converters simplify design of a variety of power supplies, including those with isolated multi-output, or positive and negative voltage rails.
• COT control architecture provides excellent load transient response and eliminates loop compensation, lowering cost and simplifying design.
• Integrated high-side and low-side N-Channel MOSFETs improve efficiency and eliminate external Schottky diode.

Packaging and pricing

The new Fly-Buck converters are offered in thermally-enhanced 8-pin LLP and PSOP packages, the LM25017 is priced at US$1.25, the LM25018 is US$1.12 and the LM25018 is US$1.00 in 1,000-unit quantities. AECQ-100 qualified versions will be available in May 2013.

For more information visit the TI website