System Board 6788

MAXREFDES1050: -15V/1.5A Buck-Boost DC-DC Converter Using the Step-Down Controller MAX17504

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Input Type VIN (MIN)
Isolated/Non-Isolated Topology
DC 18 30 1.5 Single -15 22.5 Non-Isolated Buck-Boost

The MAXREFDES1050 is a positive input, negative output power supply that delivers up to 1.5A at -15V from a 18V to 30V supply voltage. It is designed for industrial control equipment that uses analog components like amplifiers and multiplexers that operate on negative supply voltage. Typically operating at ±12V, ±18V or other variations, these voltages are generated from a 24V DC bus. The MAXREFDES1050 illustrates techniques using the synchronous buck regulators to generate negative voltages. This document explains how the MAX17504 synchronous step-down converter can be used to generate -15V from 18V to 30V input voltage. An overview of the design specification is shown in Table 1. The MAX17504/MAX17504S high-efficiency, highvoltage, synchronously rectified step-down converter with dual integrated MOSFETs operates over a 4.5V to 60V input. Maxim’s portfolio of high-voltage synchronous buck regulators offers 50% lower power loss, which allows equipment to operate 50% cooler. The device features a peak-current-mode control architecture with a MODE feature that can be used to operate the device in pulsewidth modulation (PWM), pulse-frequency modulation (PFM), or discontinuous mode (DCM) control schemes. Built-in compensation across the output voltage range eliminates the need for external components. The feedback (FB) regulation accuracy over -40°C to +125°C is ±1.1%. 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. The device is available in a compact (5mm x 5mm) TQFN lead (Pb)-free package with an exposed pad. Simulation models are available.

MAXREFDES1050 Board Enlarge+

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Designed, Built, Tested

This reference design describes the hardware shown in Figure 1. It provides a detailed systematic technical guide to design a buck-boost converter using Maxim’s MAX17504 step-down controller. The converter has been built and tested, details of which follow later in this document.

Design Resources


4.5V–60V, 3.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter with Internal Compensation

  • Eliminates External Components and Reduces Total Cost
  • Reduce Number of DC-DC Regulators to Stock
  • Reduce Power Dissipation