Electronic Design

Popular Buck Switchers Expand Online Tools, Reduce Noise Sensitivity

If you're designing mid- to low-volume systems with a buck converter in the power chain, you may have used one of National Semiconductor's Simple Switcher voltage-regulator chips, which now offer a couple of new wrinkles. An enhancement in the Webench design environment already makes using these switchers "simple." Meanwhile, a novel technique reduces noise susceptibility in current-mode feedback.

Webench online design tools span a range of National products. For Simple Switchers, it has always let engineers enter design parameters, from which the tool will assist in selecting a part. With that selection, the tool creates a design and supports circuit analysis. With the circuit locked in, Webench generates a schematic and bill of materials. The engineer then can order a prototype kit for overnight delivery.

Now, designers can optimize for efficiency and footprint by virtually tweaking "knobs" on the user interface. The new chips also feature "emulated" current mode feedback. Instead of directly measuring the current through the buck regulator coil, the control loop samples the diode current before switching occurs and sums this with an internal ramp current.

The 0.5-A LM5574, 1.5-A LM5575, and 3.0-A LM5576 have a 6- to 75-V input range. Switching frequency can be adjusted from 50 to 500 kHz. The input range for the 0.5-A LM25574, 1.5-A LM25575, and 3.0-A LM25576 is 6 to 42 V. Any switching frequency between 50 kHz and 1 MHz can be used in the design. Prices range from $1.35 to $2.90.

National Semiconductor

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