National Semiconductor Introduces New PWM Buck Controller

National Semiconductor Corp. introduced a new pulse-width modulation (PWM) buck controller that employs National's emulated-current-mode (ECM) architecture for output voltages with extremely low duty cycles at frequencies up to 1.5 MHz.

The LM3495 powers digital application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), digital signal processors (DSPs) and other embedded processors. Deep sub-micron ICs require tight regulation accuracies in order to perform, and the LM3495 offers accuracy of plus or minus 1% over a wide temperature range. It has a host of system integration features optimized for these applications. The LM3495 also addresses the additional requirements of point-of-load (POL) module manufacturers with fault-protection features.

National's new LM3495 expands the company's power management portfolio, giving designers a choice between National's ECM architecture and existing voltage-mode portfolio, the LM274x family. Both architectures allow designers to reach very high operating frequencies and conversion ratios without having to deal with switching noise headaches. National first introduced its ECM architecture with the LM5005 and plans to use it in new products to be introduced throughout the rest of the year, including a dual-output, second-generation, ECM controller designed to optimize performance in the most demanding digital cores.

In addition to its ECM control and highly accurate feedback voltage, the LM3495 includes a host of features that ease the design-in process while also ensuring reliable system performance. The LM3495 has an input voltage from 2.9 to 18V for use in 3.3, 5.0, and 12V and intermediate-bus systems, as well as an output voltage that is adjustable from 0.6 to 5.5V for existing and future core and I/O voltages. The controller has low-side sensing and a programmable current limit that does not require a sense resistor. This allows for reduced power dissipation, component count and system cost. In addition, the LM3495 has input under-voltage lockout, switch-node short protection, adaptive duty cycle limit and hiccup-mode current limit protection that eliminates thermal runaway during fault conditions. It also has an internal soft start with tracking capability.

The LM3495 has a 200 kHz to 1.5 MHz switching frequency that can be synchronized to reduce radiated system noise. Its on-chip gate drivers are capable of driving FETs suitable for output currents in excess of 20A. The LM3495 has soft shutdown and glitch-free start-up into pre-biased loads to ensure deep sub-micron cores are not damaged. The LM3495, available in a TSSOP-16 package, operates from a single input rail, eliminating the need for an external bias supply. Available now, the LM3495 is priced starting at $3.08 in 1,000-unit quantities.