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National opts for familiar outline for dc/dc modules

 

National Semiconductor has entered the market for highly integrated power modules with a range of step-down dc/dc converters in a new package. Some packages that other vendors have employed for such modules have had limitations, National asserts. With multiple contact patches on their bases, they have been difficult to prototype and have been liable to soldering errors in production. National has therefore designed a package that is in the style of a TO-263; it has a single thermal pad on its underside—that you reflowsolder to a suitable area of copper on your PCB—and all other electrical connections emerge as leads on one edge of the moulding. Internally a dual-lead-frame construction connects the controller IC, the power FETs and the passives, and offers higher reliability than simply using an over-moulded substrate, the company claims.

National will have three device families in this Simple Switcher-branded grouping, which will carry LMZ part numbers, for inputs from 3.3, 5, 12 or 24V. At introduction, there is one device for each voltage rail, and National will introduce additional parts throughout 2010. The fi rst devices do not have any new silicon—they use controllers and FETs from National’s existing catalogue— but subsequent releases will host entirely new components. Later devices will extend current capacity beyond the 5A limit of the fi rst modules in the series.

The package construction includes shielded inductors to yield low radiated EMI (electromagnetic interference), meeting the requirements of the EN55022 (CISPR22) Class B radiated-emission standard. A National spokesman comments, “The great majority of our early-adopter lead customers have opted for the devices because of their noise performance.” The modules’ effi cient heat dissipation and large exposed- bottom pad allows for operation in high-ambient temperatures without the need for airfl ow. They typically operate at as much as 10°C less than comparable modules, National claims.

For operation from -40 to +125°C, the first release of the LMZ power modules supports the common 3.3, 5, 12 and 24V input-voltage rails and offers load currents of up to 4A. Available in seven-lead, 10.16x13.77x4.57-mm packages, they have a thermalresistance (theta-JA) temperature of 20°C/W.

The LMZ10504 supports a maximum load current of 4A with an input-voltage range from 2.95 to 5.5V; the LMZ12003 supports a maximum load current of 3A with an inputvoltage range of 4.5 to 20V; and the LMZ14203 supports a maximum load current of 3A with an input-voltage range of 6 to 42V. They cost, respectively, $7.10, $7.25, and $9.50 (500).

You can design-in the modules using a new upgrade of National’s Webench software, which now handles the design of multiple output dc/dc power supplies. The software explores a number of variables, including topology, intermediate voltage rails, footprint, effi ciency, component count and BOM (bill-of-materials) cost. Under Webench Power Architect you list the inputs and outputs that your system requires and set an optimisation target that ranges from best results for minimum footprint to maximum effi ciency. The package will evaluate a number of possible confi gurations of intermediate-rail PSU architecture, presenting you with area, effi ciency and cost outcomes. You can then reoptimise your design—at this level the Flash-based client software runs in seconds—or alternatively invoke a full simulation to verify the design’s outcome. Cost information comes from a continuously updated database that National extracts from links to its network of international, broadline distributors. It covers 21,000 components from 110 manufacturers.

The software will handle system- input sources (V_in) from 1 to 100V, up to 20 system loads (V_out) from 0.6 to 300V, power per load up to 300W, a system effi ciency greater than 90%, and per-supply footprints from 14x14 mm. When the design is complete, the tool generates a system summary report including schematics, BOMs and electrical operating values, and you can invoke a “Build It!” feature to order a prototype kit.

National Semiconductor, www.national.com;

Webench demonstration at: www.national.com/ powerarchitect.