NATIONAL SEMICONDUCTOR Corp. seems to be intent on simplifying power-supply design to the point that virtually any engineer can produce an efficient, stable design. To accomplish this, National is offering the LMZ Series SIMPLE SWITCHER® power-supply module family (Fig. 1), and WEBENCH® online design support, to simplify power supply design for FPGAs, microprocessors, DSPs, and other powered subsystems.
The LMZ modules require only three resistors, as well as one input and two output capacitors. In contrast, its 20-year-old predecessor — the original Simple Switcher — requires an inductor and several external components.
The modules feature an integrated solution that can save design time, is simple to use, and reduces time-to-market. And, the modules exhibit good efficiency compared with competitive units, as seen in Fig. 2.
The first available power modules feature a conventional buck topology with an internal shielded inductor. Other topologies will follow and will also include the internal shielded inductor. Completely enclosing the power-supply circuit in a single, self-contained package helps to avoid frequency compensation and complex layout placement challenges typical in switching regulator designs.
Patent-pending packaging technology provides low radiated EMI, enabling these power modules to meet the requirements of the EN55022 (CISPR22) Class B radiated emission standard. Fig. 3 illustrates the radiated emissions of an LMZ10504 with a VIN = 5 V, VOUT = 2.5 V, and IOUT = 4 A.
Efficient heat dissipation and a large exposed bottom copper pad enable operation without the need for forced airflow, which allows the LMZ Series to operate as much as 10°C cooler (typ) than competitive modules. The exposed-bottom copper pad also facilitates relatively fast prototyping on lab benches, which eliminates the possibility of non-visual solder bridging.
The size and lead pitch of these modules enable the use of standard pick-and-place manufacturing equipment employed with standard TO-263 packages. Plus, designers can create one PC board layout for all members of the series. This facilitates last-minute drop-in replacements because all module family members are pin-to-pin compatible.
These new power modules operate in temperatures from -40° to 125°C. The devices provide a low output-voltage ripple as well as a wide voltage and current range that enables the design of a completely user-specific power-supply solution. The first release of the LMZ power modules supports the common 3.3-, 5-, 12-, and 24-V input-voltage rails and handles load currents to 4 A.
Available in a seven-lead package measuring 10.16 × 13.77 × 4.57 mm, the LMZ devices feature a thermal resistance (RθJA) of 20°C/W. Fig. 4 shows the first available series of these buck modules.
One of the first three introductions is the LMZ10504, which supports a maximum load of 4 A and features an input-voltage range from 2.95 to 5.5 V. The LMZ12003 supports maximum loads of 3 A with an input-voltage range of 4.5 to 20 V.
The LMZ14203 also supports 3-A loads but offers an input-voltage range of 6 to 42 V. Fig. 5 shows a demo board with an LMZ10504.
The LMZ10504 is priced at $7.10, the LMZ12003 sells for $7.25, and the LMZ14203 is $9.50 each in 500-unit quantities.
WEBENCH POWER DESIGNER
Neophyte power-supply designers can design these Simple Switcher power modules using National's WEBENCH® Power Designer, as well as the new WEBENCH Power Architect design tool. The enhanced WEBENCH Power Architect enables engineers to rapidly create multi-output dc-dc power supplies for an entire system (Fig. 6).
The WEBENCH Power Architect features an optimization adjustment capability (Fig. 7) that enables designers to produce designs that meet one of five different design requirements:
Optimization 1. Smallest footprint, highest frequency
Optimization 2. Low cost with high frequency for small components
Optimization 3. Balanced design: efficiency, footprint, low complexity, and cost are all important
Optimization 4. Low cost with frequency pushed lower for increased efficiency
Optimization 5. Highest efficiency, but largest components