Controller Optimizes High- to Low-Voltage Power Conversion

Apr 1, 2003 12:00 PM
By Ashok Bindra,Editor, Power Electronics Technology

Aiming to bolster its position in next-generation communications infrastructure space and automotive applications, National Semiconductor recently launched an integrated controller-driver chipset for high-voltage power conversion applications. This current-fed push-pull pulse-width modulated (PWM) controller LM5041 works seamlessly with the 100V power MOSFET driver LM5101/2 to deliver efficiencies in excess of 90% for 48V to sub 2.5V and below conversion.

This chipset is designed to efficiently step down from 48V to sub 1V output with up to 50A output current capability. It employs 2-stage conversion architecture, wherein a buck regulation stage is followed or cascaded by a push-pull isolation stage (see the figure). Although the push-pull stage can be driven by internal gate drivers, the buck stage is driven by external high-voltage buck stage gate drivers, like the LM5101/2. It also permits user-programmable dead time. This topology eliminates the buck stage capacitor and output filter inductor, and the current sense resistor. As a result, no output voltage regulation error is induced from the inductor connection resistances. Furthermore, the push-pull transformer is driven at exactly 50% duty cycle to generate a continuous power flow to the outputs — and at half the switching frequency of the buck stage, thus reducing switching losses. Also, because the power switches in the push-pull stage are rated at lower voltage, conduction losses are lower.

To pack high-voltage Power ICs in a tiny, thermally enhanced surface-mount package, this topology is combined with high-voltage process advances and packaging improvements. Toward that goal, National has developed a high-voltage (100V) 1.5 micron analog bipolar-CMOS-DMOS (ABCD) process that can furnish power MOSFETs and diodes capable of withstanding 100V and higher transients. This high-voltage process, called ABCD150HV/XV1, allows n-channel DMOS power transistors, high-voltage PMOS devices, and junction isolation diode to withstand worst-case 100V+ transients.

The LM5041 controller comes in a thermally enhanced, surface-mount leadless leadframe package LLP-16. The MOSFET driver LM5101 comes in LLP-10. Sampling now, they're slated for production in the second quarter of 2003.

Tapping these advances, National is extending its high-voltage to low-voltage power conversion portfolio with a 100V push-pull PWM controller with two built-in 2A power MOSFET drivers. Designated LM5030, this current-mode controller incorporates the features necessary to develop state-of-the-art push-pull and bridge topologies. Unlike the 5041, the LM5030 is a single stage design aimed at 3.3V and higher voltage outputs.

Features of the chip include a programmable oscillator with external synchronization, a 15V to 100V start-up bias regulator, two high-speed 2A (peak) power MOSFET drivers, a high gain-bandwidth error amplifier, a precision bandgap reference of 2.5V, programmable softstart, remote and thermal shutdown, current-mode control with internal slope compensation, dual-mode overcurrent protection, and direct opto-coupler interface.

Using this controller, National has readied a push-pull demo circuit with 3.3V output at up to 10A output current for a typical 48V input. Internal measurements show that this LM5030 based dc-dc converter offers 82.5% conversion efficiency at 10A output current, which rises to 84.5% as the output current is drops to 5A at 3.3V output voltage. The demo board size is 2.4 mm × 2.4 mm × 0.45 mm.

The LM5030 is sampling now and going into volume production next month. It's available in MSOP-10 and LLP-10 packages.

National Semiconductor Corp., Santa Clara, Calif.
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