The TPS40009 is a voltage-mode, synchronous buck PWM controller that uses TI's proprietary Predictive Gate Drive technology to wring maximum efficiency from step-down converters. This controller provides a bootstrap charging circuit to allow the use of an N-channel MOSFET as the topside buck switch to reduce conduction losses and increase silicon device utilization. Predictive Gate Drive technology controls the delay from main switch turn-off to synchronous rectifier turn-on and also the delay from rectifier turn-off to main switch turn-on. This allows minimization of the losses in the MOSFET body diodes by reducing conduction and reverse recovery time. This user's guide provides details on a 5-A buck converter that converts 3.3 V down to a 1.2-V level using the TPS40009 controller, with less than one square inch board area.