RT6259BHGQW 3A, 18V, 650kHz, ACOT™ Synchronous Step-Down Converter

Purpose

The RT6259BH are high-performance 650kHz 3A step-down regulators with internal power switches and synchronous rectifiers. This document explains the function and use of the RT6259BH 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 RT6259BH are high-performance 650kHz 3A step-down regulators with internal power switches and synchronous rectifiers. The feature quick transient response using 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 0.765V to 7V. 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 RT6259BH are stable with and optimized for ceramic output capacitors. With internal 70mΩ switches and 70mΩ synchronous rectifiers, the RT6259BH display excellent efficiency and good behavior across a range of applications, especially for low output voltages and low duty cycles. Cycle-bycycle current limit, input under-voltage lock-out, externallyadjustable soft-start, output under- and over-voltage protection, and thermal shutdown provide safe and smooth operation in all operating conditions. The RT6259BH is available in WQFN-16L 3x3 package, with exposed thermal pads.

Product Feature

• Fast Transient Response
• Steady 650kHz Switching Frequency at all Load Current
• 3A Output Current
• Advanced Constant On-Time (ACOT™) Control
• Optimized for Ceramic Output Capacitors
• 4.5V to 18V Input Voltage Range
• Internal 70mΩ Switch and 70mΩ Synchronous Rectifier
• 0.765V to 7V Adjustable Output Voltage
• Externally-adjustable, Pre-biased Compatible Soft-Start
• Cycle-by-Cycle Current Limit
• Optional Output Discharge Function
• With Hiccup Mode Output Over- and Under-voltage Shut-down protection
• Input Under-Voltage Lockout
• 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 (4.5 < V_IN < 18V) to the VIN and GND terminals.

2. Set the jumper at JP2 to connect terminals 2 and 3, connecting EN to enable operation.

3. Set the jumper at JP1 to connect terminals 1 and 2, power VCC pin by VIN voltage source.

4. Verify the output voltage (approximately 1.05V) between VOUT and GND.

5. Connect an external load up to 3A 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)