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

EVB_RT6238AHGQUF

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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.

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

Key Features

Evaluation Board Number : PCB063_V1

Input Voltage Range

12V

Max Output Current

8A

Default Output Voltage

1.0V

Default Marking & Package Type

RT6238AHGQUF, UQFN-14L 2x3 (FC)

Operation Frequency

Steady 500kHz at all loads



Bench Test Setup Conditions

Headers Description and Placement

Technical Document Image Preview

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.

Test Point/

Pin Name

Signal Name

Description

VIN

Input Voltage

Power input. The input voltage range is from 4.5V to 18V. Must bypass with a suitably large (≥10µF x 2) ceramic capacitor.

EN

Enable

Enable control input. A logic-high enables the converter; a logic-low forces the IC into shutdown mode reducing the supply current to less than 10µA. Attach this pin to PVCC with a 100kW pull-up resistor for automatic start-up.

GND

Ground

Ground.

VPVCC

Internal Regulator Output

Internal regulator output. Connect a 1µF capacitor to GND to stabilize output voltage.

PG

Power Good Output

Power good indicator open-drain output.

BOOT

Bootstrap Supply

Connect a capacitor between the SW and BOOT pins to form a floating supply across the power switch driver. A 0.1µF capacitor is recommended for use.

SW

Switch Node

Connect this pin to an external L-C filter.

SS

Soft-Start Control

An external capacitor should be connected between this pin and GND.



Power-Up & Measurement Procedure

1. Apply a 12V nominal input power supply (4.5V < VIN < 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 :

Technical Document Image Preview



Schematic, Bill of Materials & Board Layout

EVB Schematic Diagram

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Bill of Materials

Reference

Qty

Part Number

Description

Package

Manufacturer

U1

1

RT6238AHGQUF

DC-DC Converter

UQFN-14L 2x3 (FC)

RICHTEK

C1, C12

2

NC

C3, C4

2

C3216X5R1E106KT000E

10µF/25V/X5R

C-1210

TDK

C5

1

C1608X5R1E105KT000E

1µF/25V/X5R

C-0603

TDK

C6, C8

2

C1608X7R1H104KT000N

0.1µF/50V/X7R

C-0603

TDK

C7

1

0603B103K500

10nF/50V/X7R

C-0603

WALSIN

C9, C10, C11

3

C3225X5R1E226MT000E

22µF/16V/X5R

C-1210

TDK

R2, R4

2

0603T-1-20K

20k

R-0603

旺詮

R3

1

0603T-1-46K4

46.4k

R-0603

旺詮

R5

1

0603 100K 1%

100k

R-0603

WALSIN

L1

1

NC

L2

1

7443340100

1µH

L-744325120

Wurth Elektronik



PCB Layout

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Top View (1st layer)

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PCB Layout—Inner Side (2nd Layer)

Technical Document Image Preview

PCB Layout—Inner Side (3rd Layer)

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Bottom View (4th Layer)

Title Last Update Share Download
Evaluation Board User Guide 2016/08/12
Bill of Materials 2016/08/12
Gerber File 2016/08/12
Schematic 2016/08/12
RT6238A/RT6238B

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

RT6238A/RT6238B

The RT6238A/B 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 (ACOTTM) 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 ACOTTM 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 RT6238A/B is stable with and optimized for ceramic output capacitors. With internal 35mΩ switches and 14mΩ synchronous rectifiers, the RT6238A/B 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/B is available in the UQFN-14L 2x3 (FC) package, with exposed thermal pad.

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