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3A, 36V, 500kHz Current Mode Asynchronous Step-Down Converter

EVB_RT2808AGSP

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The RT2808A 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 3A. 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 shut down mode, the regulator draws only 25μA of supply current. The RT2808A requires a minimum number of readily available external components, providing a compact solution. The RT2808A provides protection functions inducing input under voltage lockout, cycle-by-cycle current limit, short circuit protection and thermal shutdown protection.The RT2808A is available in the SOP-8 (Exposed Pad) package.

Purpose

The RT2808A is a current mode asynchronous step-down converter that achieves excellent load and line regulation. This document explains the function and use of the RT2808A 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 RT2808A 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 3A. 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 shut down mode, the regulator draws only 25μA of supply current. The RT2808A requires a minimum number of readily available external components, providing a compact solution. The RT2808A provides protection functions inducing input under voltage lockout, cycle-by-cycle current limit, short circuit protection and thermal shutdown protection.The RT2808A is available in the SOP-8 (Exposed Pad) package.


Product Features

  • 3A 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

 

Key Performance Summary Table

Key Features

Evaluation Board Number : PCB011_V1

Default VIN Input Voltage

12V

Max Output Current

3A

Default Output Voltage

2.5V

Default Marking & Package Type

RT2808AGSP, SOP-8 (Exposed Pad)



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. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation.



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

3

A

Current Limit

ILIM

4

5.25

6.5

A



Schematic, Bill of Materials & Board Layout

EVB Schematic Diagram

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Bill of Materials

Reference

Qty

P/N

Description

Package

Manufacture

U1

1

RT2808AGSP

Step-down converter

SOP-8

(Exposed Pad)

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

NR8040T6R8N

6.8µH

TAIYO YUDEN

D1

1

B550C

50V/5A

DIODES

R1, R2, R4

3

100k

R-0402

C8, R5

2

NC



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)

Step-Down Converter Efficiency Test

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Title Last Update Share Download
Evaluation Board User Guide 2015/10/28
Bill of Materials 2015/10/28
Gerber File 2015/10/28
Schematic 2015/10/28
RT2808A

3A, 36V, 500kHz Current Mode Asynchronous Step-Down Converter

RT2808A

The RT2808A 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 3A. 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 RT2808A requires a minimum number of readily available external components, providing a compact solution. The RT2808A provides protection functions inducing input under voltage lockout, cycle-by-cycle current limit, short circuit protection and thermal shutdown protection. The RT2808A is available in the SOP-8 (Exposed Pad) package.

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