PWM controllers suit general applications

Edited by the Electronicstalk editorial team Oct 26, 2007

STMicroelectronics' pulse width modulation controllers allow a significant reduction in the cost and size of the power supply.

STMicroelectronics has released PWM (pulse width modulation) controllers intended for motherboard and POL (point of load) markets.

The L6726A, L6727, L6728 and L6728A integrate a voltage reference, control logic, gate drivers, monitoring and protection circuits into standard SO-8 or tiny 3x3mm DFN packages.

Two of the chips offer additional features for high-level applications, including a PowerGood output to report power status and the output voltage sense for accurate over-voltage and under-voltage protection.

The L6726A and L6727 are low-cost single-phase PWM controllers, with embedded high-current drivers, enabling the easy creation of general purpose DC/DC step-down convertors for applications from desktop PC sub-systems, such as memories and chipsets, to general-purpose power supplies.

These compact SO-8 devices allow a significant reduction in the cost and size of the power supply.

The L6728 and L6728A add to the simpler devices the characteristics required by the high-end motherboard market, +/- 0.8% voltage accuracy over line and temperature variations, a PowerGood output to provide real-time information on output-voltage status and the chip-scale 10-lead DFN package.

They offer a fixed-frequency 300kHz (L6728) or 600kHz (L6728A) oscillator, for simple but flexible application design.

It is the first time that all of these features have been integrated into such a small package and the devices are particularly suited to servers and niPOL (nonisolated point of load) applications.

In addition to use on server and PC motherboards, the controllers are suitable for modems, set-top boxes (STBs), consumer applications and advanced DC/DC down-convertors.

With embedded high-current, high-speed N-channel MOSFET drivers, the chips can be used in the design of power applications driving a few Amps to more than 30A.

They operate over a wide input voltage range of 1.5V to 18V, while the integrated 0.8V voltage reference ensures 1% (L6726A, L6727) or up to 0.8% (L6728, L6728A) output accuracy.

Sensorless current monitoring, through a low-side power MOSFET, avoids the cost of an external current-sensing resistor and saves board space and the single or dual-level over-current protection has programmable thresholds.

A range of other features are designed to increase efficiency and reduce the external component count.