RT5785AGJ8F
Evaluation Board
your power partner.
2A, 6V, 1.5MHz, 25µA IQ, ACOT™ Synchronous Step-Down
Converter
Purpose
The RT5785A is a current mode step-down converter with the input voltage range from 2.5V to 6V and provides 2A
output current. This document explains the function and use of the RT5785A 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
Bench Test Setup Conditions ........................................................................................................................................3
Schematic, Bill of Materials & Board Layout.................................................................................................................5
More Information ...........................................................................................................................................................8
Important Notice for Richtek Evaluation Board.............................................................................................................8
EVB_RT5785AGJ8F-00
November
2016
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RT5785AGJ8F
Evaluation Board
your power partner.
Introduction
General Product Information
The RT5785A is a high-performance, Advanced Constant On-Time (ACOT™) monolithic synchronous step-down
DC/DC converter that can deliver up to 2A output current from a 2.5V to 6V input supply. The proprietary ACOT
control architecture features quick transient response and provides stable operation with small ceramic output
capacitors and without complicated external compensation. The switching ripple voltage is easily smoothed–out by
small package filtering elements due to a constant switching frequency of 1.5MHz and the maximum duty cycle of
100% allows the device to operate at low dropout use. With internal low on-resistance power switches and
extremely low quiescent current, the RT5785A displays excellent efficiency and good behavior across a range of
applications. Cycle-by-cycle current limit provides protection against shorted outputs, input under-voltage lock-out,
output under-voltage protection, and thermal shutdown provide safe and smooth operation in all operating
conditions. The RT5785A is available in the TSOT-23-8 (FC) package.
Product Feature
Dramatically Fast Transient Response
Steady 1.5MHz ±200kHz Switching Frequency
Very Low Input Quiescent and Shutdown Currents
Advanced COT Control Loop Design
Optimized for Ceramic Output Capacitors
2.5V to 6V Input Voltage Range
Accurate Voltage Reference 0.6V ±2%
Integrated 100m/60m MOSFETs
Internal Start-Up into Pre-biased Outputs
Power Good Indicator
Enable Control
Over-Current and Over-Temperature Protections
Under-Voltage Protection with Hiccup Mode
RoHS Compliant and Halogen Free
Key Performance Summary Table
Key Features
Evaluation Board Number: PCB079_V1
Default Input Voltage
5V
Max Output Current
2A
Default Output Voltage
1.0V
Default Marking & Package Type
RT5785AGJ8F, TSOT-23-8 (FC)
Operation Frequency
Steady 1.5MHz at all loads
EVB_RT5785AGJ8F-00
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2016
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RT5785AGJ8F
Evaluation Board
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Bench Test Setup Conditions
Headers Description and Placement
Carefully inspect all the components used in the EVB according to the following Bill of Materials table, and
then make sure all the components are undamaged and correctly installed. If there is any missing or
damaged component, which may occur during transportation, please contact our distributors or e-mail us at
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
Supply Input. Supplies the power to the internal control circuit as well as the power
switches of the device. Drive VIN with a 2.5V to 6V power source and bypass VIN
to PGND with a suitably large capacitor to eliminate noise on the input to the IC.
EN
Enable test point
Enable Control Input. Connecting this pin to logic high can enable the device and
connecting this pin to GND can disable the device.
PGND
Ground
Power Ground. This pin must be soldered to a large PCB and connected to analog
ground for maximum power dissipation.
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 0.6V typically.
PGOOD
Power Good test point
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 UVP, OTP, dropout, EN shutdown, or during slow start.
VOUT
Output Voltage
Output Voltage Sense Input. This pin is used to monitor and adjust output voltage
for superior load transient regulation.
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.
AGND
Ground
Analog Ground. Provides the ground return path for control circuitry and internal
reference.
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2016
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Power-up & Measurement Procedure
1. Connect input power (2.5V < VIN < 6V) and input ground to VIN and GND test pins respectively.
2. Connect positive end and negative terminals of load to VOUT and GND test pins respectively.
3. There is a 3-pin header “EN” for enable control. To use a jumper at “H” option to tie EN test pin to input power
VIN for enabling the device. Inversely, to use a jumper at “L” option to tie EN test pin and ground GND for
disabling the device.
4. Verify the output voltage (approximately 1.0V) between VOUT and GND.
5. Connect an external load up to 2A 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:
VOUT = VFB x (1 + R1 / R2)
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2016
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Schematic, Bill of Materials & Board Layout
EVB Schematic Diagram
Bill of Materials
Reference
Qty
Part number
Description
Package
Manufacturer
U1
1
RT5785AGJ8F
RT5785AGJ8F
TSOT-23-8 (FC)
RICHTEK
ROUT, A-PGND
2
0R
0R/0603
REN2, CF2, CFF,
CEN, C1, C5
6
NC
NC
C2, C4
2
10μF/16V
10μF/25V/X5R/1206
TDK
C3, C6
2
0.1μF/0603
0.1μF/±10%/50V/X7R/0603
TDK
J1
1
EN
單排排針
L
1
1.0μH
1.0μH/4.2A/6mm*6mm
REN1, RPG
2
100k/0603
100k/0603
WALSIN
R1
1
200k/0603
200k/0603
WALSIN
R2
1
300k/0603
300k/0603
WALSIN
EVB_RT5785AGJ8F-00
November
2016
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WALSIN
6x6x4.5mm
TAIYO YUDEN
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RT5785AGJ8F
Evaluation Board
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PCB Layout
st
Top View (1 layer)
PCB Layout—Inner Side (2
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2016
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nd
Layer)
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RT5785AGJ8F
Evaluation Board
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rd
PCB Layout—Inner Side (3 Layer)
th
Bottom View (4 Layer)
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2016
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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 TO
BUYER OR USER FOR ANY AND ALL DAMAGES INCLUDING WITHOUT LIMITATION TO DIRECT, INDIRECT, SPECIAL, PUNITIVE OR CONSEQUENTIAL
DAMAGES.
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2016
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