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RT2805A Step-Down Converter Evaluation Board

EVB_RT2805AGSP

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The RT2805A is a current mode asynchronous step-down converter that achieves excellent load and line regulation. Over a wide input voltage range from 5.5V to 36V and supports output current up to 5A. The Current mode operation provides fast transient response and eases loop stabilization. An adjustable soft-start reduces the stress on the input source at start up. In shutdown mode, the regulator draws only 25μA of supply current. The RT2805A requires a minimum number of readily available external components, providing a compact solution. The RT2805A provides protection functions inducing input under voltage lockout, cycle-by-cycle current limit, short circuit protection and thermal shutdown protection. The RT2805A is available in the SOP-8 (Exposed Pad) package.

Purpose

The RT2805A is a current mode asynchronous step-down converter that achieves excellent load and line regulation. This document explains the function and use of the RT2805A evaluation board (EVB) and provides information to enable operation and modification of the evaluation board and circuit to suit individual requirements.


Introduction

General Product Description

The RT2805A is a current mode asynchronous step-down converter that achieves excellent load and line regulation. Over a wide input voltage range from 5.5V to 36V and supports output current up to 5A. The Current mode operation provides fast transient response and eases loop stabilization. An adjustable soft-start reduces the stress on the input source at start up. In shutdown mode, the regulator draws only 25μA of supply current. The RT2805A requires a minimum number of readily available external components, providing a compact solution. The RT2805A provides protection functions inducing input under voltage lockout, cycle-by-cycle current limit, short circuit protection and thermal shutdown protection. The RT2805A is available in the SOP-8 (Exposed Pad) package.

Product Features

  • 5A Output Current
  • Wide Operating Input Range 5.5V to 36V
  • Adjustable Output Voltage from 1.222V to 26V
  • High Efficiency up to 90%
  • Internal Compensation Minimizes External Parts Count
  • Internal Soft-Start
  • 110mΩ Internal Power MOSFET Switch
  • 25μA Shutdown Mode
  • Fixed 500kHz Frequency
  • Thermal Shutdown
  • Cycle-by-Cycle Current Limit
  • Available In an SOP-8 (Exposed Pad) Package
  • RoHS Compliant and Halogen Free


Application

  • Distributive Power Systems
  • Battery Charger
  • DSL Modems
  • Pre-regulator for Linear Regulators


Bench Test Setup Conditions 

Headers Description and Placement

Technical Document Image Preview

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.

Test point/
Pin name

Signal

Comment (expected waveforms or voltage levels on test points)

VIN

Input voltage

Input voltage range = 5.5V to 36V

VOUT

Output voltage

Output voltage = 2.4V

SW

Switch Node

EN

Chip Enable Operation

The EN pin is externally pulled to High by adding a 100kΩ resistor (R4) from the VIN pin in this EVB setting. For another enable operation, the converter is turned on when the EN pin is higher than 1.4V and turned off when the EN pin is lower than 0.4V.

GND

Ground

Ground


Power-up & Measurement Procedure

1. Connect input power (5.5V < VIN < 36V) and input ground to VIN and GND pins respectively.

2. Connect positive end and negative end of load to VOUT and GND of output pins respectively.

3. The output voltage of (VOUT) can be set by R1 and R2.

VOUT = VREF * (1 + R1 / R2)

where VREF = 1.222V (typ.)


Specification

Parameter

Symbol

Min

Typ.

Max

Units

Input Voltage Range

VIN

5.5

36

V

Output Voltage

VOUT

2.4

V

Oscillator Frequency

fOSC

400

500

600

kHz

Output Current

IOUT

5

A

Current Limit

ILIM

6

7.5

9

A


Schematic

Technical Document Image Preview


BOM

Reference

Q'ty

P/N

Description

Package

Manufacture

U1

1

RT2805AGSP

Step-down converter

SOP-8

RICHTEK

C1, C2

2

GRM32ER71H475K

4.7μF/50V/X7R

C-1210

MURATA

C3, C6, C11

3

C1608X7R1H104K080AA

0.1μF/±10%/50V/X7R

C-0603

TDK

C4, C5

2

GRM32ER61C226KE20

22μF/±10%/16V/X5R

C-1210

MURATA

C12

1

82pF

C-0603

L1

1

74437368068

6.8μH, 6A, ±20%, DCR = 23.3mΩ

10 x 10 x 3.8mm

WE-LHMI

D1

1

B550C

50V/5A

DIODES

R1, R2, R4

3

100k

R-0402

C8, R5

2

NC


PCB Layout

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PCB Layout (1st layer)

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PCB Layout (2nd layer)

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PCB Layout (3rd layer)

Technical Document Image Preview

PCB Layout (4th layer)


Step-Down Converter Efficiency Test

Technical Document Image Preview

Title Last Update Share Download
Evaluation Board User Guide 2015/08/21
Bill of Materials 2015/08/21
Gerber File 2015/09/18
Schematic 2015/09/18
RT2805A

5A, 36V, 500kHz Current Mode Asynchronous Step-Down Converter

RT2805A

The RT2805A is a current mode asynchronous step-down converter that achieves excellent load and line regulation. Over a wide input voltage range from 5.5V to 36V and supports output current up to 5A. The Current mode operation provides fast transient response and eases loop stabilization.

An adjustable soft-start reduces the stress on the input source at startup. In shutdown mode, the regulator draws only 25µA of supply current. The RT2805A requires a minimum number of readily available external components, providing a compact solution. The RT2805A provides protection functions inducing input under voltage lockout, cycle-by-cycle current limit, short circuit protection and thermal shutdown protection.

The RT2805A is available in the SOP-8 (Exposed Pad) package.

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