RT2855ALGQW
Evaluation Board
your power partner.
4A, 18V, 650kHz, ACOT™ Synchronous Step-Down Converter
Purpose
The RT2855A 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
RT2855A evaluation board (EVB), and provides information to enable operation, modification of the evaluation
board and circuit to suit individual requirements.
Table of Contents
Purpose ................................................................................................................................................................. 1
Introduction............................................................................................................................................................ 2
Key Performance Summary Table .......................................................................................................................... 2
Bench Test Setup Conditions ................................................................................................................................. 3
Schematic, Bill of Materials & Board Layout ........................................................................................................... 5
More Information.................................................................................................................................................... 8
Important Notice for Richtek Evaluation Board ....................................................................................................... 8
EVB_RT2855ALGQW-00
October 2015
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RT2855ALGQW
Evaluation Board
your power partner.
Introduction
General Product Information
The RT2855A 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
Discontinuous operating mode at Light 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 Latched
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
RT2855ALGQW, WQFN-16 3x3
EVB_RT2855ALGQW-00
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RT2855ALGQW
Evaluation Board
your power partner.
Bench Test Setup Conditions
Headers Description and Placement
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).
EVB_RT2855ALGQW-00
October 2015
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RT2855ALGQW
Evaluation Board
your power partner.
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 :
VOUT = 0.765 x (1 +
EVB_RT2855ALGQW-00
R2
)
R3
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RT2855ALGQW
Evaluation Board
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Schematic, Bill of Materials & Board Layout
EVB Schematic Diagram
Bill of Materials
Reference
Qty
Part Number
Description
Package
Manufacture
U4
1
RT2855ALGQW
DC/DC Converter
WQFN-16 3x3
RICHTEK
C1
1
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
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
EVB_RT2855ALGQW-00
NC
NR8040T1R4N
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Evaluation Board
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PCB Layout
Top View (1st layer)
PCB Layout—Inner Side (2nd Layer)
EVB_RT2855ALGQW-00
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RT2855ALGQW
Evaluation Board
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PCB Layout—Inner Side (3rd Layer)
Bottom View (4th Layer)
EVB_RT2855ALGQW-00
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RT2855ALGQW
Evaluation Board
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More Information
For more information, please find the related datasheet or application notes from Richtek website
http://www.richtek.com.
Important Notice for Richtek Evaluation Board
THIS DOCUMENT IS FOR REFERENCE ONLY, NOTHING CONTAINED IN THIS DOCUMENT SHALL BE CONSTRUED AS RICHTEK’S WARRANTY, EXPRESS
OR IMPLIED, UNDER CONTRACT, TORT OR STATUTORY, WITH RESPECT TO THE PRESENTATION HEREIN. IN NO EVENT SHALL RICHTEK BE LIABLE T O
BUYER OR USER FOR ANY AND ALL DAMAGES INCLUDING WITHOUT LIMITATION TO DIRECT, INDIRECT, SPECIAL, PUNITIVE OR CONSEQUENTIAL
DAMAGES.
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