The LM27402 is a feature-rich, synchronous, single phase PWM DC/DC buck controller. A wide input voltage range of 3-V to 20-V, input voltage feedforward, and dual high current integrated N-channel MOSFET drivers make the LM27402 appropriate for high current intermediate bus system rails in point-of-load applications. A 0.6-V ±1% internal voltage reference enables high accuracy and low voltage capability at the output. Inductor DCR current sensing provides an accurate current limit detection method and promotes high output current and high system efficiency by eliminating resistive current sense elements.

This user's guide describes the steps taken in selecting the external components to build a fully functional DC/DC converter. This user's guide includes diagrams of the evaluation board layout and bill of materials. The evaluation board represents a typical application circuit and can be modified if different specifications are desired. Refer to the LM27402 High Performance Synchronous Buck Controller with DCR Current Sensing data sheet for additional design equations.

The LM27402 evaluation board represents a 20-A typical application circuit. The application circuit is optimized for an input voltage of 12 V. However, input voltage feedforward technology allows the evaluation board to operate up to 20 V while maintaining a stable output voltage of 1.5 V at 20 A. Temperature compensated inductor DCR current limit circuitry provides a steady current limit set point. Extra MOSFET and input/output capacitor footprints are included to accommodate higher currents if desired. An externally set soft-start time of 10 ms provides a controlled monotonic start-up. The LM27402 evaluation board also supports pre-biased start-up and provides a tracking connection for power supply sequencing. An external clock can be applied to change the switching frequency through an on board synchronization connection. PGOOD is externally pulled up to VDD and can be monitored via an on board terminal. Two extra terminals are included to provide a network analyzer connection for control loop stability analysis. The PCB measures 1.3 inch × 1.8 inch and includes input/output banana connectors for the input supply and load.

• Input Voltage = 4.5 V to 20 V
• Output Voltage = 1.5 V
• Output Current = 0 A to 20 A

Figure 3-1 Simplified Application Schematic