MAXREFDES1142: Ultra-small two-layer, 4A, 1.8V step-down DC-DC converter with integrated switch using the MAX15051

The MAX15051 is a high-efficiency switching regulator that delivers up to 4A load current at output voltages from 0.6V to (0.9 x VIN). The device operates from 2.9V to 5.5V, making it ideal for on-board point-of-load and postregulation applications. The total output-voltage accuracy is within ±1% over load, line, and temperature.

The MAX15051 features 1MHz fixed-frequency PWM operation, and pulse-skip mode to improve light-load efficiency. The high operating frequency allows for small-size external components. The low-resistance on-chip nMOS switches ensure high efficiency at heavy loads while minimizing critical parasitic inductances, making the layout a much simpler task with respect to discrete solutions.

The device incorporates a high-bandwidth (> 26MHz) voltage-error amplifier. The voltage-mode control architecture and the voltage-error amplifier permit a Type III compensation scheme to achieve maximum loop bandwidth, up to 200kHz. High loop bandwidth provides fast transient response, resulting in less required output capacitance and allowing for all-ceramic capacitor designs.

The output overload hiccup protection and peak current limit on both high-side and low-side MOSFETs provide for ultra-safe operation in the cases of short-circuit conditions, severe overloads, or in converters with bulk electrolytic capacitors.

The output voltage is adjustable by using two external resistors at the feedback or by applying an external reference voltage to the REFIN/SS input.

The MAX15051 offers a programmable soft-start time using one capacitor to reduce input inrush current. A built-in thermal shutdown protection ensures safe operation under all conditions. Other features include the following:

Key Features

• 20μA Startup Current in UVLO
• Programmable Input Undervoltage Lockout
• Programmable Input Overvoltage Protection
• Switching Frequency Synchronization
• Adjustable Soft-Start
• Programmable Slope Compensation
• Fast Cycle-by-Cycle Peak Current Limit
• 70ns Internal Leading-Edge Current-Sense Blanking
• Hiccup Mode Output Short-Circuit Protection

This board is not available for purchase.

Designed, Built, Tested

This document describes the hardware shown in Figure 1. It provides a detailed systematic technical guide to designing a step-down (buck) converter using Maxim's MAX15051 voltage mode controller. The power supply has been built and tested, details of which follow later in this document.

Design Resources