National Semiconductor Corp has added six buck switching regulators to its Simple Switcher regulator family, and also enhanced their related Webench design tool. Six new regulators extend the input voltage range to 75V, with continuous output rating up to 3A. To provide improved transient performance, critical in many applications, the regulators implement closed-loop operation using emulator-current-mode (ECM) technology (patented).
Operating frequency is 50 kHz to 1 MHz, and each device has a frequency synchronization pin so its operating frequency can be slaved to an external source, or multiple regulators sync'ed to each other, to control and minimize EMI. Short-circuit protection, thermal shutdown, and cycle-by-cycle current limiting is standard, as well.
The ECM technique avoids the problems introduced by trying to directly measure the inductor current, often done using a small current-sensing resistor which affects loop performance. In ECM, the circuit measures the inductor voltage from which it can infer the current ramp; it also measures the current through the feedback diode using a small resistor, which is a much less intrusive position than a sensing resistor in series with the inductor. The result is improved transient performance and the ability to operate at extremely low duty cycles for improved low-load efficiency.
The six parts just released all accept VIN starting at 6 Vdc and going up to either 42 or 75 V; output range goes from 1.225 V to VIN :
Along with the new switchers, National has also updated the Webench design tool which simplifies the user's selection of parts and designs. Using this tool, you enter the desired key performance requirements, and it returns a list of possible ICs to consider (and includes LDOs). For each regulator, it shows a schematic and bill of materials (including specific passive-component vendors and specific models), and also shows the resultant footprint and efficiency for the nominal design. Webench also runs full electrical and thermal simulations.
Then the tool lets you work the tradeoffs. You can “dial-in” a new value (higher or lower) for either footprint or efficiency, and Webench returns a modified design. For example, you may find that pushing for a few more percentage points in efficiency costs a few more percent in footprint–and that's an acceptable tradeoff. Or you need a smaller footprint, and accept that the impact is slightly lower efficiency.
The Simple Switcher regulators are priced between $1.35 and $2.90 each in 1,000-piece lots; the WeBench tool is free at www.switcher.national.com.
National Semiconductor Corp. , Santa Clara, CA, www.national.com