Power Electronics

Buck Regulators Boast Better Performance, Easier Optimization

National Semiconductor has expanded it popular Simple Switcher product family by adding six buck regulators with improved performance, while also enhancing its Webench design tool so users can more easily make design tradeoffs. The new Simple Switcher models feature a proprietary form of current-mode control that enables fast transient response in combination with low-duty cycle operation; adjustable, high-frequency switching, and an extended input voltage range. Engineers can configure and optimize designs using these parts in Webench using a “Dial-in performance” feature that allows users to tradeoff efficiency and pc-board footprint.

The new Simple Switcher models include the 0.5-A LM5574 and LM25574, the 1.5-A LM5575 and 1.5-A LM25575, and the 3.0-A LM5576 and LM25576. Like other family members, the new ICs are nonsynchronous buck regulators. However, whereas the previous family members used voltage-mode control, the six additions employ National’s emulated current-mode control, which the company first deployed in its LM5005 controller.

This control technique overcomes noise problems that limit minimum on-time (and therefore minimum duty cycle) in regulators using traditional peak current-mode control. The newest Simple Switchers can achieve a minimum on-time of 80 ns (typ.) (For more on this control method, see “Control Method Solves Low Duty-Cycle Dilemmas”in the September 2006 issue of Power Electronics Technology.)

That performance can be used to achieve higher stepdown ratios and higher switching frequencies. Meanwhile, current-mode control also enables the newest Simple Switchers to achieve better transient response than their predecessors.

The existing Simple Switchers operate at fixed switching frequencies up to 260 kHz. In contrast, the new models operate at an adjustable switching frequency as high as 1 MHz. Input voltage range is another distinction. The previous models could accept inputs as high as 60 V, though most only went up to 40 V. However, the new models can operate from inputs as high as 75 V. Input voltages may be as low as 6 V.

The buck regulators also provide a frequency synchronization pin, which allows multiple ICs from the family to self-synchronize or to synchronize to an external clock. The new regulators guarantee robustness with cycle-by-cycle current limit, short-circuit protection and thermal shut-down.

“Combined with National’s Webench suite of tools, Simple Switcher regulators allow design engineers to make decisions about their power supply design, such as the trade-off between size and efficiency,“ said Mal Humphrey, product line director for National’s Power Management Group. “Any engineer, including seasoned power supply designers, can create, optimize and analyze their design in just one minute.

The buck regulators are offered in 16- and 20-pin TSSOPs with exposed thermal pads.

Prices for the products range from $1.35 to $2.90 in 1000-unit quantities.
For more information or to order samples and evaluation boards, see the following links:
www.national.com/pf/LM/LM5574.html
www.national.com/pf/LM/LM25574.html
www.national.com/pf/LM/LM5575.html
www.national.com/pf/LM/LM25575.html.
www.national.com/pf/LM/LM5576.html
www.national.com/pf/LM/LM25576.html.

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