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User's Guide
SNVA406B–May 2010–Revised May 2013
AN-1992 LM27402 Evaluation Board
1 Introduction
The LM27402 is a feature-rich, synchronous, single phase PWM DC/DC buck controller. A wide input
voltage range of 3V to 20V, input voltage feed-forward, 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 0.6V ±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 application note describes the steps taken in selecting the external components to build a fully
functional DC/DC converter. Diagrams of the evaluation board layout and bill of materials are included at
the end of this application note. The evaluation board represents a typical application circuit and can be
modified if different specifications are desired. Please refer to the Design Guide section of the LM27402
High Performance Synchronous Buck Controller with DCR Current Sensing (SNVS615) data sheet for
additional design equations.
2 Evaluation Board
The LM27402 evaluation board represents a 20A typical application circuit. The application circuit is
optimized for an input voltage of 12V. However, input voltage feed-forward technology allows the
evaluation board to operate up to 20V while maintaining a stable output voltage of 1.5V at 20A.
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 startup. The LM27402
evaluation board also supports pre-biased startup 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” x 1.8” and includes input/output banana connectors for the input
supply and load.
3 Evaluation Board Operating Specifications
• Input Voltage = 4.5V to 20V
• Output Voltage = 1.5V
• Output Current = 0A to 20A
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SNVA406B–May 2010–Revised May 2013 AN-1992 LM27402 Evaluation Board
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