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Electronic Design

Fully Functional Spice Simulator Gets Optimized For Switchers

Adding speed and convergence to original Spice code, Linear Technology Corp. of Milpitas, Calif., has developed a fully functional Spice simulator that includes schematic-capture and waveform display capabilities. Proprietary convergence, time-step control, and analog behavioral modeling have been weaved into conventional Spice to create a fast and accurate simulation engine for LTC's switchers.

The SwitcherCAD III is optimized to provide transient simulation of complex switching-regulator circuits on a cycle-by-cycle basis 10 times faster than conventional methods, LTC claims. The company is offering the simulator, which can be downloaded from LTC's Web site, at no cost to users.

This simulator includes a library of macro models comprising over 100 of LTC's switching regulators and 200 general-purpose op amps, along with other mixed-mode building blocks. Currently, over 400 LTC products are modeled in the SwitcherCAD III library, and the company plans to continually add new models. "With a Web update feature built into the program, users will be able to download new models and program changes via the Internet," says Robert Dobkin, LTC's chief technical officer.

"Since it is generic Spice and offers an open database, users can add proprietary circuits and other discrete component models to this library," Dobkin notes. LTC intends to expand the library with linear regulators, voltage references, interfaces, charge pumps, and other functions. Further details on new models for other functions were unavailable, though.

After capturing the circuit, circuit models are linked into the schematic for simulation (see the figure). The program lets users change component values and observe the response graphically using the waveform viewer. A waveform calculator permits data manipulation.

The company believes SwitcherCAD III is faster than PSpice. According to LTC, internal tests show that SwitcherCAD III is as accurate as PSpice when all the parasitic components are set correctly. Also, it can quickly simulate a power-supply system. Bench measurements are in good agreement with the simulation results as well, the supplier says. Generally, the accuracy is within 10% to 20%. In addition, the program generates a bill of materials (BOM) for the circuit designed and simulated, along with the vendor list for passive components.

This simulator comes on the heels of other major suppliers offering online design, analysis, and simulation tools for their parts. National Semiconductor and Fairchild Semiconductor have created free Internet workbenches in conjunction with simulation software developer Transim Corp.

Recently, National Semiconductor revamped its online power-supply simulation tool to include thermal simulation and the ability to generate the BOM for the intended design (see "Interactive Online Design Tools Expedite Prototyping," electronic design analog supplement, Nov. 20, 2000, p. 11). By teaming with Pioneer-Standard Electronics and Vishay Intertechnology, National Semiconductor has taken its online simulation engine a step further. Now, by linking to, the user can place an order for the BOM resulting from the circuit designed and simulated. Pioneer says the entire prototype kit can be delivered overnight.

For a free download of the SwitcherCAD III program, point your browser to

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