6A, 18V, 650kHz, ACOT™ Synchronous Step-Down Converter

Purpose

The RT6236AH is a Advanced Constant On-Time (ACOT™) control architecture step-down converter with the input voltage range from 4.5V to 18V and provides 6A output current. This document explains the function and use of the RT6236AH 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 RT6236AH is a high-performance 650kHz, 6A 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. The input voltage range is from 4.5V to 18V and the output is adjustable from 0.7V to 8V. The proprietary ACOT™ control improves upon other fast response constant on-time architectures, achieving nearly constant switching frequency over line, load, and output voltage ranges. Since there is no internal clock, response to transients is nearly instantaneous and inductor current can ramp quickly to maintain output regulation without large bulk output capacitance. The RT6236AH is stable with and optimized for ceramic output capacitors. With internal 51mΩ switches and 18mΩ synchronous rectifiers, the RT6236AH 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 lock-out, externally-adjustable soft-start, output under- and over-voltage protection, and thermal shutdown provide safe and smooth operation in all operating conditions. The RT6236AH is available in the UQFN-13JL 2x3 (FC) package, with exposed thermal pad.

Product Feature

• Fast Transient Response
• Advanced Constant On-Time (ACOT™) Control
• 4.5V to 18V Input Voltage Range
• Adjustable Output Voltage from 0.7V to 8V
• 6A Output Current
• 51mΩ Internal High-Side N-MOSFET and 18mΩ Internal Low-Side N-MOSFET
• Steady 650kHz 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

Please carefully inspect the EVB IC and external components, comparing them to the following Bill of Materials, to ensure that all components are installed and undamaged. If any components are missing or damaged during transportation, please contact the distributor or send e-mail to 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 JP2 to connect terminals 2 and 3, connecting EN to VIN through resistor R5, to enable operation.

3. Verify the output voltage (approximately 1.2V) between VOUT and GND.

4. Connect an external load up to 5A 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)