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Richtek

4A, 18V, 650kHz, ACOT™ Synchronous Step-Down Converter

EVB_RT2855BHGQW

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The RT2855BH is a high-performance 650kHz 4A 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. The input voltage range is from 4.5V to 18V and the output is adjustable from 0.765V to 7V.

Purpose

The RT2855BH is an Advanced Constant On-Time (ACOT™) control architecture step-down converter with the input voltage range from 4.5V to 18V and provides 4A output current. This document explains the function and use of the RT2855BH 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 RT2855BH is a high-performance 650kHz 4A 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. The input voltage range is from 4.5V to 18V and the output is adjustable from 0.765V to 7V.


Product Feature

  • Fast Transient Response
  • Steady 650kHz Switching Frequency at all Load
  • 4A Output Current
  • Advanced Constant On-Time (ACOT™) Control
  • Optimized for Ceramic Output Capacitors
  • 4.5V to 18V Input Voltage Range
  • Internal 70mΩ Switch and 30mΩ Synchronous Rectifier
  • 0.765V to 7V Adjustable Output Voltage
  • Externally-adjustable, Pre-biased Compatible Soft-Start
  • Cycle-by-Cycle Current Limit
  • Optional Output Discharge Function
  • Output Over- and Under-voltage Shut-down in Hiccup Mode
  • Input Under Voltage Lockout
  • Thermal Shutdown

 

Key Performance Summary Table

Key Features

Evaluation Board Number : PCB023_V1

Default Input Voltage

12V

Max Output Current

4A

Default Output Voltage

1.05V

Default Marking & Package Type

RT2855BHGQW, WQFN-16 3x3



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

Power input. Support 4.5V to18V Input Voltage. Must bypass with a suitable large ceramic capacitor at this pin.

EN

Enable test point

A logic-high enables the converter; a logic-low forces the IC into shutdown mode reducing the supply current to less than 10µA.

GND

Ground

Ground.

VCC

Internal regulator output

VCC supplies power for the internal linear regulator that powers the IC. Connect VIN to the input voltage and bypass to ground with a 0.1µF ceramic capacitor.

BOOT

Bootstrap supply test point

Bootstrap supply for high-side gate driver. Connect a 0.1µF capacitor

between BOOT and SW to power the internal gate driver.

SW

Switch node test point

SW is the source of the internal N-channel MOSFET switchand the drain of the internal N-channel MOSFET synchronous rectifier. Connect SW to the inductor with a wide short PCB trace and minimize its area to reduce EMI.

VREG5

Internal regulator

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

SS

Soft-start control

Connect an external capacitor between this pin and GND to set the soft-start time.

PG

Open drain power good output

PGOOD connects to PGND whenever VFB is less than 90% of its regulation threshold (typical).



Power-up & Measurement Procedure

1. Apply a 12V nominal input power supply (4.5V < VIN < 18V) to the VIN and GND terminals.

2. Connect JP1 to connect VIN to VCC. Set the jumper at JP2 to connect terminals 2 and 3, connecting EN to VCC to enable operation.

3. Verify the output voltage (approximately 1.05V) between VOUT and GND.

4. Connect an external load up to 4A 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

Manufacture

U4

1

RT2855BHGQW

DC/DC Converter

WQFN-16 3x3

RICHTEK

C1

1

NC

C2, C5, C6, C8, C12

5

C1608X7R1H104K080AA

0.1μF/±10%/50V/X7R

C-0603

TDK

C3, C4

2

UMK325BJ106MM

10µF/50V/X7R

C-1210

TAIYO YUDEN

C7

1

0603B332K500

3.3nF/50V/X7R

C-0603

WALSIN

C9

1

C3225X5R1E226MT

22µF/25V/X5R

C-1210

TDK

C10

1

C3225X5R1E226MT

22µF/25V/X5R

C-1210

TDK

C13

1

NA

C14

1

NA

L1

1

NR8040T1R4N

1.4µH/7A

8 x 8 x 4.2 mm

TAIYO YUDEN

R1

1

0

R-0603

R2

1

8.25k

R-0603

R3

1

22.1k

R-0603

R4, R5

2

100k

R-0603

R6, R7

2

NA



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 2015/10/27
Bill of Materials 2015/10/27
Gerber File 2015/10/27
Schematic 2015/10/27
RT2855A/RT2855B

4A, 18V, 650kHz, ACOT® 同步 Buck 轉換器

RT2855A/RT2855B

RT2855A/B 是集成了功率開關和同步整流器的高性能 650kHz 4A 降壓轉換器,它們採用了具有快速瞬態回應能力的先進的固定導通時間( ACOT® )控制架構,能與小容量的陶瓷輸出電容配合穩定工作,無需使用複雜的外部補償電路。其輸入電壓範圍為 4.5V~18V ,輸出電壓可在 0.765V~7V 間可調。立錡專有的 ACOT® 控制架構是對具有快速瞬態回應能力的 COT 架構的改良,使之具有了幾乎固定的開關工作頻率,與供電、負載和輸出電壓範圍不再有關聯。由於沒有內部時鐘,它對瞬變過程的回應幾乎是即時的,其電感電流可以快速變化以維持輸出電壓的穩定,無需使用大型輸出電容。RT2855A/B 在使用陶瓷輸出電容時是穩定的,而且特別對此進行了優化。借助 70mΩ 的開關和 30mΩ 的同步整流器,RT2855A/B 表現出卓越的轉換效率,在各種應用中表現良好,在低輸出電壓和低責任週期的應用中的表現尤其突出。它具有逐週期電流限制、輸入欠壓鎖定、外部可調軟啟動、輸出欠壓和過壓保護和熱關機保護等功能,可在各種工作條件下安全使用。RT2855A 和 RT2855B 均使用了 WQFN-16L 3x3 的封裝。在輕載條件下,RT2855B 採用連續切換的策略以避免可能的低頻串擾,RT2855A 則進入節能的非連續操作模式以避免效率下降。

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