PWM Controllers Integrate Four Bridge MOSFET Drivers

April 13, 2011

New full-bridge pulse-width-modulation (PWM) controllers developed by National Semiconductor Corp. incorporate all four primary-side bridge MOSFET gate drivers. The LM5045 and LM5046 are the latest members of NSC’s PowerWise family.

The LM5045 PWM controller’s features enable implementation of a conventional full-bridge topology power converter using either current- or voltage-mode control. And for applications requiring zero-voltage switching (ZVS) to minimise electromagnetic interference (EMI) caused by switching noise, the LM5046 PWM controller delivers the features necessary to implement a phase-shifted full-bridge topology.

Offered in small, thermally enhanced 5.0- by 5.0- by 0.8-mm LLP and 4.4- by 9.7- 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 100V. They provide robust 2A high- and low-side gate drivers for the four external bridge MOSFETs, in addition to the control signals for the secondary-side synchronous-rectifier (SR) MOSFETs and an internal high-voltage startup regulator. Intelligent startup of the SRs allows for monotonic turn-on of the power converter, even with pre-bias load conditions. 

The SR control signals offer independent and programmable leading/trailing-edge dead-times between the primary and secondary MOSFET control signals to optimise efficiency. The signals are limited to 5V when used with digital isolators.

Also included is dual-mode overcurrent protection featuring 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 synchronisable 2MHz oscillator, and thermal shutdown.

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