PWM controller aims for intermediate power bus

The LM5033 is billed as the industry's first fully featured 100V DC/DC PWM controller that meets the challenging specifications of the intermediate bus architecture.

The LM5033 is billed as the industry's first fully featured 100V DC/DC PWM (pulsewidth modulation) controller that meets the challenging specifications of the intermediate bus architecture (IBA).

This recently introduced architecture controls the multiple low-voltage power supply rails in complex power systems using digital ASICs, DSPs and FPGAs that are found in telecommunications, automotive and industrial applications.

As designers continue to enhance convertor performance and power density, traditional power conversion techniques are giving way to new distributed power architectures such as the IBA.

The IBA consists of an isolated bus convertor powered from a higher-voltage distributed power rail that produces an "intermediate" lower voltage distribution bus, typically 8 to 14V, to feed multiple nonisolated regulators at the point of load.

As the IBA uses two stages of power conversion, the bus convertor and point-of-load regulators must be more efficient and fit in a smaller board area to offer a compelling alternative to single-stage distributed power systems.

To address these challenges, National designed the LM5033 PWM controller with the flexibility to be used stand-alone in a push-pull bus convertor or paired with one or two of National's LM5100 drivers in a half- or full-bridge convertor design.

This flexibility allows designers to produce a family of bus convertors that deliver a wide range of output power levels for telecom and computing power systems.

"The introduction of the intermediate bus is an inflection point in the evolution of distributed power architectures", said Paul Greenland, Marketing Director for National Semiconductor's Power Management group.

"Customers expect the next generation of intermediate bus convertors to be flexible and efficient without sacrificing real estate".

"National has stepped up to the challenge with the LM5033, which is an optimum solution because of a flexible architecture that enables designers to use it in three different topologies".

Designed on National's new analogue-BiCMOS-DMOS high-voltage process technology, the LM5033 operates off a wide range of input voltages from 15 to 100V for lower component count and higher efficiency.

It also has efficient PWM and gate driver performance at frequencies up to 1MHz.

The LM5033 is a highly integrated, voltage-mode PWM controller with an internal high-voltage startup regulator that offers the following performance, space and heat benefits: a megahertz oscillator that shrinks power transformer and filter components to save space and improve transient response; less than 100ns propagation delay on current limit permits smaller margins in the power train components; 1.5 A mosfet drivers are capable of driving larger mosfets for higher power throughput; and switching frequency set by a single resistor.

The LM5033 may be synchronised, which reduces EMI, crosstalk and interference, and permits blanking during the power-switching interval in sensitive load circuits.

Current sense with front-edge blanking protects the power switches without tripping on the leading-edge spike, while hiccup mode reduces device stress and power dissipation during overload or short circuit The direct optocoupler interface means that no external pull-up resistor is required.

Minimum dead-time guarantees robust performance.

Voltage mode control, which is better for half-bridge convertors, has higher control noise immunity than current mode control.

The reference pin may be used for primary control and housekeeping functions.

Soft start reduces inrush current, permitting sequencing and direct control of the output stages.

Undervoltage lockout with hysteresis prevents malfunctions during startup or brownouts.

The 10-lead LLP package has a 4 x 4mm footprint.

Available today, National's LM5033 is priced at US $1.10 each in 1000-off volumes.

The LM5100 is also available now in a SOIC or LLP package at $1.35 each in 1000-off volumes.

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