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RT2875B Synchronous Step-Down Converter Evaluation Board

EVB_RT2875BQGCP

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The RT2875B is a high efficiency, current-mode synchronous DC/DC step-down converter that can deliver up to 3A output current over a wide input voltage range from 4.5V to 36V. The device integrates 95mΩ high-side and 70mΩ low-side MOSFETs to achieve high conversion efficiency. The current-mode control architecture supports fast transient response and simple external compensation. A cycle-by-cycle current limit function provides protection. against shorted output and an external soft-start eliminates input current surge during start-up. The RT2875B provides complete protection functions such as input under-voltage lockout, output under-voltage protection, over-current protection and thermal shutdown.The RT2875B is available in the thermal enhanced TSSOP-14 (Exposed Pad) package.

Purpose

The RT2875B is a high efficiency, current-mode synchronous DC/DC step-down converter that can deliver up to 3A output current over a wide input voltage range from 4.5V to 36V. his document explains the function and use of the RT2875B 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 RT2875B is a high efficiency, current-mode synchronous DC/DC step-down converter that can deliver up to 3A output current over a wide input voltage range from 4.5V to 36V. The device integrates 95mΩ high-side and 70mΩ low-side MOSFETs to achieve high conversion efficiency. The current-mode control architecture supports fast transient response and simple external compensation. A cycle-by-cycle current limit function provides protection. against shorted output and an external soft-start eliminates input current surge during start-up. The RT2875B provides complete protection functions such as input under-voltage lockout, output under-voltage protection, over-current protection and thermal shutdown.The RT2875B is available in the thermal enhanced TSSOP-14 (Exposed Pad) package.

The RT2875B provides Hiccup Mode Under Voltage Protection (UVP). When the VFB voltage drops below 0.3V, the UVP function will be triggered to shut down switching operation. If the UVP condition remains for a period, the RT2875B will retry automatically. When the UVP condition is removed, the converter will resume operation. The UVP is disabled during soft-start period.


Product Features

  • 3A Output Current
  • Internal N-MOSFETs
  • Current Mode Control
  • Adjustable Switching Frequency : 300kHz to 2.1MHz
  • Adjustable Current Limit : 1.5A to 6A
  • Synchronous to External Clock : 300kHz to 2.1MHz
  • Adjustable Output Voltage from 0.6V to 24V
  • High Efficiency Up to 95%
  • Stable with Low ESR Ceramic Output Capacitors
  • Cycle-by-Cycle Current Limit
  • Input Under-Voltage Lockout
  • Output Under-Voltage Protection
  • Thermal Shutdown
  • RoHS Compliant and Halogen Free

 

Application

  • Point of Load Regulator in Distributed Power Systems
  • Digital Set Top Boxes
  • Broadband Communications

 

Key Performance Summary Table

Key Features

Evaluation Board Number : PCB013_V1

Default Input Voltage

12V

Max Output Current

3A

Default Output Voltage

3.3V

Default Marking & Package Type

RT2875BQGCP, TSSOP-14 (Exposed Pad)

Operation Frequency

300kHz to 2.1MHz (Adjusted by RT Value, Defult RT = 100k,
Frequency = 500kHz)



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)

SW

Switch Node

Connect to external L-C filter.

PGND

Power Ground

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

RT/SYNC

Oscillator Resistor

Oscillator Resistor and External Frequency Synchronization Input. Must connect a resistor from this pin to GND to set the switching frequency. If SYNC clock is requested, connect an external clock to change the switching frequency.

AGND

Analog Ground

Ground.

RLIM

Current Limit Setting

Connect a resistor from this pin to GND to set the current limit value.

FB

Feedback Voltage Input

The pin is used to set the output voltage of the converter to regulate to the desired via a resistive divider. Feedback reference = 0.6V.

COMP

Compensation Node.

COMP is used to compensate the regulation control loop. Connect a series RC network from COMP to GND. In some cases, an additional capacitor from COMP to GND is required.

SS

Soft-Start Time Setting.

Connect a capacitor from SS to GND to set the soft-start period.

EN

Enable

Enable Control Input. High = Enable.

PGOOD

Power Good Output.

Power Good Indicator Output.

VIN

Input Voltage

Input voltage range = 4.5V to 36V.

BOOT

Boot

Bootstrap Supply for High-Side Gate Driver. Connect a 0.1µF ceramic capacitor between the BOOT and SW pins.



Power-up & Measurement Procedure

1. Connect input power (4.5V< 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 = 0.6V (typ.)


Specification

Parameter

Symbol

Min

Typ.

Max

Units

Input Voltage Range

VIN

4.5

36

V

Oscillator Frequency

fOSC

300

2100

kHz

Output Current

IOUT

3

A

EN Input Voltage

VEN

1.4

1.5

1.6

V



Schematic, Bill of Materials & Board Layout

EVB Schematic Diagram

Technical Document Image Preview



Bill of Materials

Reference

Q'ty

Part Number

Description

Package

Manufacture

U2

1

RT2875BQGCP

Step-down Converter

PTSSOP-14

RICHTEK

Css, C3,
C6, C11

4

C1608X7R1H104KT000N

0.1μF/50V/X7R

C-0603

TDK

C1, C2

2

GRM32ER71H106KA12

10μF/50V/X7R

C-1210

Murata

C4, C5

2

GRM32ER61C226KE20L

22μF/16V/X5R

C-1210

MURATA

C7

1

0603B333K500

3.3nF/50V/X7R

C-0603

WALSIN

R5, C8, C9, C12, C13

5

NC

C/R-0603

D1

0

NC

D2

0

NC

L1

1

NR8040T4R7N

4.7μH

8040

TAIYO YUDEN

744 771 404 7

4.7μH/7A

WE

RT, R4, RPG

3

100K

R-0603

RLIM

1

33k

R-0603

R1

1

115K

R-0603

R2

1

25.5K

R-0603

R3

1

10K

R-0603



PCB Layout

Technical Document Image Preview

Top View (1st layer)

Technical Document Image Preview

PCB Layout—Inner Side (2nd Layer)

Technical Document Image Preview

PCB Layout—Inner Side (3rd Layer)

Technical Document Image Preview

Bottom View (4th Layer)



Step-Down Converter Efficiency Test

Technical Document Image Preview

Title Last Update Share Download
Evaluation Board User Guide 2015/11/26
Bill of Materials 2015/11/26
Gerber File 2015/11/26
Schematic 2015/11/26
RT2875A/RT2875B

3A, 36V 同步降壓轉換器

RT2875A/RT2875B

RT2875A/B 是高效的電流模式同步降壓 DC/DC 轉換器,可在 4.5V~36V 的輸入電壓範圍內輸出 3A 電流。它集成了 95mΩ/70mΩ 功率開關,可獲得很高的轉換效率。電流模式的控制架構容許其具有快速的瞬態回應能力,僅需使用簡單的外部補償。逐週期電流限制功能賦予其對抗輸出短路的能力,外部可調的軟啟動消除了啟動期間的輸入電流衝擊。它還具有完善的保護功能,如輸入欠壓鎖定、輸出欠壓保護、過流保護和熱關機保護等。RT2875A/B 使用的是熱強化的 TSSOP-14(含外露的散熱焊盤)封裝。

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