New PWM controllers integrate all four primary-side bridge MOSFET gate drivers

March 07, 2011 // By Paul Buckley
National Semiconductor Corp., has unveiled what the company claims is the industry’s first full-bridge pulse width modulation (PWM) controllers to integrate all four primary-side bridge MOSFET gate drivers. The LM5045 and LM5046 are well-suited for delivering higher efficiency and higher power density in quarter-brick and eighth-brick power modules used in a variety of high input voltage communications infrastructure applications.

Members of National’s PowerWise energy-efficient product family, the LM5045 and LM5046 PWM controllers ease the design of full-bridge topology-based power converters into small form factor power supplies by reducing the number of external power components needed with existing full-bridge solutions. 

The LM5045 PWM controller contains all of the features necessary to implement a conventional full-bridge topology power converter using either current mode or voltage mode control.  For applications requiring zero-voltage switching (ZVS) to minimize electro-magnetic interference (EMI) due to switching noise, the LM5046 PWM controller contains all the features necessary to implement a phase-shifted full-bridge topology.

Offered in small, thermally enhanced 5.0 mm by 5.0 mm by 0.8 mm LLP and 4.4 mm by 9.7 mm by 0.9 mm TSSOP packages, the full-bridge controllers operate on the primary side of an isolated DC-DC converter with input voltage up to 100 V.  The highly integrated controllers provide robust 2 A high and low side gate drivers for the four external bridge MOSFETs in addition to the control signals for the secondary side synchronous rectifier MOSFETs and an internal high voltage start-up regulator.  Intelligent start-up of the synchronous rectifiers (SR) allows monotonic turn-on of the power converter, even with pre-bias load conditions. 

The synchronous rectifier control signals offer independent and programmable leading/trailing edge dead-times between the primary and secondary MOSFET control signals for optimizing efficiency, and the SR signals are limited to 5 V for use with digital isolators.  Additional features include dual mode over-current protection featuring both cycle-by-cycle current limiting and hiccup mode restart, programmable soft-start, timing for both primary and synchronous rectifiers, programmable line UVLO and OVP, a synchronizable 2 MHz oscillator and thermal shutdown.

National’s new LM5045 and LM5046, together with secondary side FET drivers such as the LM5110, LM5111 and LM5112, provide a complete controller solution to implement a highly efficient, small form factor full-bridge power converter.

Availability and Pricing

National’s new full-bridge PWM controllers are available now