MAXREFDES1019: Multi-Output DC-DC Converter Using Buck Regulator

This document describes a circuit that uses three MAX17541G buck converters and one MAX17504 step-down DC-DC converter. The circuit is arranged so that each buck converter uses the same input with four separate outputs. Each output has a different power specification. The MAX17541G regulator and features are given first, followed by the MAX17504 features.

MAX17541G

The MAX17541G high-efficiency, high-voltage, synchronous step-down DC-DC converter with integrated MOSFETs operates over a 4.5V to 42V input. The converter can deliver up to 500mA and generates output voltages from 0.9V up to 0.92 x V_IN. The feedback (FB) voltage is accurate to within ±1.7% over the -40°C to +125°C operating temperature range. The MAX17541G uses peak-current-mode control with pulse-width modulation (PWM) and operates with fixed 600kHz switching frequency at any load.

Key Features

• Reduced Power Dissipation
• Peak Efficiency > 90%
• Shutdown Current = 0.9μA (typ)
• Operates Reliably in Adverse Industrial Environments
• Hiccup-Mode Current Limit, Sink Current Limit, and Autoretry Startup
• Built-In Output-Voltage Monitoring (Active-Low RESET Pin)
• Programmable EN/UVLO Threshold
• Adjustable Soft-Start and Prebiased Power-Up
• -40°C to +125°C Ambient Operating Temperature Range/-40°C to +150°C Junction Temperature Range

MAX17504

The MAX17504 is also a high-efficiency, high-voltage, synchronous step-down DC-DC converter with integrated MOSFETs and operates over a 4.5V to 60V input. The converter can deliver up to 3.5A current. Output voltage is programmable from 0.9V to 0.9 x V_IN. The feedback voltage regulation accuracy over -40°C to +125°C is ±1.1.%. The MAX17504 also features a peak-currentmode control architecture. The device can be operated in the pulse-width modulation (PWM), pulse-frequency modulation (PFM), or discontinuous-conduction mode (DCM) control schemes. A programmable soft-start feature allows users to reduce input inrush current. The device also incorporates an output enable/undervoltage lockout pin (EN/UVLO) that allows the user to turn on the part at the desired input voltage level. An open-drain active-low RESET pin provides a delayed power-good signal to the system upon achieving successful regulation of the output voltage.

Key Features

• 100kHz to 2.2MHz Adjustable Switching Frequency with External Synchronization
• Peak Efficiency > 90%
• PFM and DCM Modes Enable Enhanced Light-Load Efficiency
• 2.8μA Shutdown Current
• Operates Reliably in Adverse Industrial Environments
• Hiccup Mode Overload Protection
• Adjustable Soft-Start and Prebiased Power-Up
• Built-In Output-Voltage Monitoring with RESET
• Programmable EN/UVLO Threshold
• -40°C to +125°C Ambient Operating Temperature Range/-40°C to +150°C Junction Temperature Range

This board is not available for purchase.

A multiple buck converter circuit using three MAX17541G devices (VOUT1,2,3) and one MAX17504 device (VOUT4) is demonstrated for a single 24V input application. The power supply delivers up to four separate outputs.

Designed, Built, Tested

This document describes the hardware shown in Figure 1. It provides a detailed systematic technical guide to designing a buck converter circuit using Maxim’s MAX17541G and MAX17504 current-mode controllers. The power supply has been built and tested, details of which follow later in this document.

Design Resources