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PWM controller promises 1 percent accuracy

Posted: 04 Aug 2006 ?? ?Print Version ?Bookmark and Share

Keywords:National? LM3495? PWM controller?

National Semiconductor Corp. has introduced a new PWM buck controller that employs the company's emulated-current-mode (ECM) architecture for output voltages with low duty cycles at frequencies up to 1.5MHz. The LM3495 powers digital ASICs, FPGAs, DSPs and other embedded processors. Deep sub-micron ICs require tight regulation accuracies in order to perform, and the new device promises accuracy of 1 percent over a wide temperature range. The new device also addresses the additional requirements of point-of-load (POL) module manufacturers with fault-protection features that ensure a reliable end product, National said.

The LM3495 expands National's power management portfolio, giving designers a choice between the company's ECM architecture and existing voltage-mode portfolio, the LM274x family. Both architectures allow designers to reach high operating frequencies and conversion ratios without having to deal with switching noise headaches, the company explained.

In addition to ECM control and accurate feedback voltage, National said the LM3495 has features that ease the design-in process while also ensuring reliable system performance. It has an input voltage from 2.9V to 18V for use in 3.3-, 5-, 12V and intermediate-bus systems, as well as an output voltage that is adjustable from 0.6V 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, the company said. In addition, the new device 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 200kHz to 1.5MHz 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. It has soft shutdown and glitch-free start-up into pre-biased loads to ensure deep sub-micron cores are not damaged. The device, available in a TSSOP-16 package, operates from a single input rail, National said, eliminating the need for an external bias supply.

Already available, the LM3495 is priced starting at $3.08 in 1,000-unit quantities.




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