8A, 18V, 500kHz, ACOT™ Synchronous Step-Down Converter

Purpose

The RT6238A is an ACOT control architecture step-down converter, which the input voltage range is from 4.5V to 18V and the output is adjustable from 0.7V to 8V. This document explains the function and use of the RT6238A evaluation board (EVB), and provides information to enable operation, modification of the evaluation board and circuit to suit individual requirements.

Introduction

General Product Information

The RT6238A is a high-performance 500kHz, 8A step-down regulator with internal power switches and synchronous rectifiers. It features quick transient response using its Advanced Constant On-Time (ACOT™) control architecture that provides stable operation with small ceramic output capacitors and without complicated external compensation, among other benefits. With internal 35mΩ switches and 14mΩ synchronous rectifiers, the RT6238A displays excellent efficiency and good behavior across a range of applications, especially for low output voltages and low duty cycles. Cycle-by-cycle current limit provides protection against shorted outputs, input under-voltage lockout, externally-adjustable soft-start, output under- and over-voltage protection, and thermal shutdown provide safe and smooth operation in all operating conditions. The RT6238A is available in the UQFN-14L 2x3 (FC) package, with exposed thermal pad.

Product Features

• Fast Transient Response
• Advanced Constant On-Time (ACOT™) Control
• 4.5V to 18V Input Voltage Range
• Adjustable Output Voltage from 0.7V to 8V
• 8A Output Current
• 35mΩ Internal High-Side N-MOSFET and 14mΩ Internal Low-Side N-MOSFET
• Steady 500kHz Switching Frequency
• Up to 95% Efficiency
• Optimized for All Ceramic Capacitors
• Externally-Adjustable, Pre-Biased Compatible Soft-Start
• Cycle-by-Cycle Current Limit
• Input Under-Voltage Lockout
• Output Over- and Under-Voltage Protection
• Power Good Output
• Thermal Shutdown

Key Performance Summary Table

Bench Test Setup Conditions

Headers Description and Placement

Carefully inspect all the components used in the EVB according to the following Bill of Materials table, and then make sure all the components are undamaged and correctly installed. If there is any missing or damaged component, which may occur during transportation, please contact our distributors or e-mail us at evb_service@richtek.com.

Test Points

The EVB is provided with the test points and pin names listed in the table below.

Power-Up & Measurement Procedure

1. Apply a 12V nominal input power supply (4.5V < V_IN < 18V) to the VIN and GND terminals.

2. Set the jumper at JP1 to connect terminals 2 and 3, connecting EN to VIN through resistor R5, to enable operation.

3. Verify the output voltage (approximately 1V) between VOUT and GND.

4. Connect an external load up to 8A to the VOUT and GND terminals and verify the output voltage and current.

Output Voltage Setting

Set the output voltage with the resistive divider (R2, R3) between VOUT and GND with the midpoint connected to FB. The output is set by the following formula :

Schematic, Bill of Materials & Board Layout

EVB Schematic Diagram

Bill of Materials

PCB Layout

Top View (1^st layer)

PCB Layout—Inner Side (2^nd Layer)

PCB Layout—Inner Side (3^rd Layer)

Bottom View (4^th Layer)