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RT2856GQW 6A, 18V, Synchronous Step-Down Converter

EVB_RT2856GQW

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The RT2856GQW is a high efficiency, monolithic synchronous step-down DC/DC converter that can deliver up to 6A output current from a 4.5V to 18V input supply. The RT2856GQW current-mode architecture with external compensation allows the transient response to be optimized over a wide range of loads and output capacitors. Cycle-by-cycle current limit provides protection against shorted outputs and soft-start eliminates input current surge during startup. Fault condition protections include output under-voltage protection, output over-voltage protection, and overtemperature protection. The low current shutdown mode provides output disconnection, enabling easy power management in battery-powered systems.

Purpose

The RT2856GQW is a current mode step-down converter with the input voltage range from 4.5V to 18V and provides 6A outputcurrent. This document explains the function and use of the RT2856GQW 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 RT2856GQW is a high efficiency, monolithic synchronous step-down DC/DC converter that can deliver up to 6A output current from a 4.5V to 18V input supply. The RT2856GQW current-mode architecture with external compensation allows the transient response to be optimized over a wide range of loads and output capacitors. Cycle-by-cycle current limit provides protection against shorted outputs and soft-start eliminates input current surge during startup. Fault condition protections include output under-voltage protection, output over-voltage protection, and overtemperature protection. The low current shutdown mode provides output disconnection, enabling easy power management in battery-powered systems.


Product Feature

  • Low RDS(ON) Power MOSFET Switches 26mΩ/19mΩ
  • Input Voltage Range : 4.5V to 18V
  • Adjustable Switching Frequency : 200kHz to 1.6MHz
  • Current-Mode Control
  • Synchronous to External Clock : 200kHz to 1.6MHz
  • Accurate Voltage Reference 0.8V±1%, Over - 40°C to 85°C
  • Monotonic Start-Up into Pre-biased Outputs
  • Adjustable Soft-Start
  • Power Good Indicator
  • Under-Voltage and Over-Voltage Protection
  • Input Under-Voltage Lockout
  • RoHS Compliant and Halogen Free

 

Key Performance Summary Table

Key Features

Evaluation Board Number : PCB069_V1

Default Input Voltage

12V

Max Output Current

6A

Default Output Voltage

3.3V

Default Marking & Package Type

RT2856GQW, WQFN-14AL 3.5x3.5

Operation Frequency

Steady 200kHz to 1.6MHz



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)

RT/SYNC

Oscillator Resistor and External Frequency Synchronization Input

Oscillator Resistor and External Frequency Synchronization Input. Connecting a resistor from this pin to GND sets the switching frequency or connecting an external clock to this pin changes the switching frequency.

GND

System Ground

System Ground. Provide the ground return path for the control circuitry and low-side power MOSFET. The exposed pad must be soldered to a large PCB and connected to GND for minimum power dissipation.

PVIN

Power Input

Power Input. Supplies the power switches of the device.

VIN

Supply Voltage Input

Supply Voltage Input. Supplies the control circuitry and internal reference of the device.

FB

Feedback Voltage Input

Feedback Voltage Input. This pin is used to set the desired output voltage via an external resistive divider. The feedback reference voltage is 0.8V typically.

COMP

Compensation Node

Compensation Node. The current comparator threshold increases with this control voltage. Connect external compensation elements to this pin to stabilize the control loop.

SS/TR

Soft-Start and Tracking Control Input

Soft-Start and Tracking Control Input. Connect a capacitor from SS to GND to set the soft-start period. The soft-start period can be used to track and sequence when the external voltage on this pin overrides the internal reference.

EN

Enable Control Input

Enable Control Input. Floating this pin or connecting this pin to logic high can enable the device and connecting this pin to GND can disable the device.

LX

Switch node test point

Switch Node. LX is the switching node that supplies power to the output and connect the output LC filter from LX to the output load.

BOOT

Bootstrap Supply for High-Side Gate Driver

Bootstrap Supply for High-Side Gate Driver. Connect a 100nF or greater capacitor from LX to BOOT to power the high-side switch.

PGOOD

Power Good Indicator Output

Power Good Indicator Output. This pin is an open-drain logic output that is pulled to ground when the output voltage is lower or higher than its specified threshold under the conditions of OVP, OTP, dropout, EN shutdown, or during slow start.



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 J9 to connect terminals 1 and 2, connecting EN to VIN through resistor REN1, to enable operation.

3. Verify the output voltage (approximately 3.3V) between VOUT and GND.

4. Connect an external load up to 6A to the VOUT and GND terminals and verify the output voltage and current.


Output Voltage Setting

Set the output voltage with the resistive divider (R1, R2) 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

Technical Document Image Preview



Bill of Materials

Reference

Qty

Part Number

Description

Package

Manufacture

U1

1

RT2856GQW

DC/DC Converter

WQFN-14AL 3.5x3.5

RICHTEK

R1

1

0603 75K0 1%

75kΩ

0603

WALSIN

R2

1

0603 24K0 1%

24kΩ

0603

WALSIN

RCOMP1

1

0603 2K40 1%

2.4kΩ

0603

WALSIN

RT, RPG1, REN1

3

0603 100K 1%

100kΩ

0603

WALSIN

C1, C2

2

UMK325BJ106MM-T

10µF/50V/X7R

1206

TAIYO YUDEN

C4

1

GRM31CR71H475KA12L

4.7µF/50V/X7R

1206

muRata

C5, C6

2

C3225X5R1E226MT

22µF/25V/X7R

1210

TDK

CCOMP1

1

0603B822K500CT

8.2nF/50V/X7R

0603

WALSIN

CCOMP2

1

0603N181J500LT

180pF/50V/X7R

0603

WALSIN

CSS

1

0603B103K500

10nF/50V/X7R

0603

WALSIN

C3, C7, CBOOT

3

C1608X7R1H104KT000N

0.1µF/50V/X7R

0603

TDK

L1

1

3.7µH

CFF, C2F, CEN, REN2, RTR1, RTR2, RPG2, D2

8

N/A



PCB Layout

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Top View (1st layer)

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PCB Layout—Inner Side (2nd Layer)

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PCB Layout—Inner Side (3rd Layer)

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Bottom View (4th Layer)

Title Last Update Share Download
Evaluation Board User Guide 2016/05/13
Bill of Materials 2016/05/13
Gerber File 2016/05/13
Schematic 2016/05/13
RT2856

6A, 18V 同步降壓型 DC/DC 轉換器

RT2856

RT2856是一款高效率、單晶同步降壓型DC/ DC轉換器,在4.5V至18V的輸入電源範圍可提供最高為6A的輸出電流。RT2856 藉由外部補償的電流模式架構使得在很寬範圍的負載及輸出電容中,都可得到最佳的瞬態回應。逐週期電流限制保護元件免受輸出短路影響;軟啟動功能可在啟動過程中防止了輸入電流過沖。故障保護包括輸出欠壓保護,輸出過壓保護,過溫保護。低電流消耗之電源關閉模式會將輸出關閉,有助於電池供電系統的電源管理。

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