Purpose
The RT5795A is an Advanced Constant-On-Time (ACOT) synchronous step-down converter with the input voltage range from 2.5V to 5.5V and provides 2A output current. This document explains the function and use of the RT5795A 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 RT5795A is a full featured 5.5V, 2A, Advanced Constant-On-Time (ACOT) synchronous step-down converter with two integrated MOSFETs. The advanced COT operation allows transient responses to be optimized over a wide range of loads, and output capacitors to efficiently reduce external component count. The RT5795A provides up to 2.7MHz switching frequency to minimize the size of output inductor and capacitors.
Product Feature
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2.5V to 5.5V Input Voltage Range
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Advanced COT Control loop design
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Fast Transient Response
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Internal 100mΩ and 80mΩ Synchronous Rectifier
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Highly Accurate VOUT Regulation Over Load/Line Range
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Robust Loop Stability with Low-ESR COUT
Key Performance Summary Table
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Key Features
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Evaluation Board Number : PCB035_V1
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Default Input Voltage
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3.3V
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Max Output Current
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2A
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Default Output Voltage
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1.2V
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Default Marking & Package Type
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RT5795AGQW, WDFN-8SL 2x2
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Operation Frequency
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Fixed 2.7MHz
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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.
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Test point/Pin name
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Signal
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Comment (expected waveforms or voltage levels on test points)
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VIN
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Input voltage
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Power input supply voltage, 2.5V to 5.5V.
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EN
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Enable test point
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Enable control input. Pull high to enable.
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PGOOD
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Power Ground
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The exposed pad must be soldered to a large PCB and connected to GND for maximum thermal dissipation.
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AGND
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Analog Ground
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Should be electrically connected to GND close to the device.
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PGND
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Power Ground
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The exposed pad must be soldered to a large PCB and connected to PGND for maximum power dissipation.
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VOS
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No internal connection
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Output voltage sense pin for the Internal Control Loop. Must be connected to output.
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FB
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Feedback test point
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Feedback voltage input.
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LX
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Switch node test point
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Switch node. The source of the internal high-side power MOSFET, and drain of the internal low-side (synchronous) rectifier MOSFET.
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Power-up & Measurement Procedure
1. Apply a 12V nominal input power supply (2.5V < VIN < 5.5V) to the VIN and GND terminals.
2. Set the jumper at JP1 to connect terminals 2 and 3, connecting EN to enable operation.
3. Verify the output voltage (approximately 1.2V) between VOUT and GND.
4. 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 (R24, R29) between VOUT and GND with the midpoint connected to FB. The output is set by the following formula :
Schematic, Bill of Materials & Board Layout
EVB Schematic Diagram
Bill of Materials
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Reference
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Qty
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Part Number
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Description
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Package
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Manufacture
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U4
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1
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RT5795AGQW
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DC/DC Converter
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WDFN-8SL 2x2
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RICHTEK
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C12, C13, C31
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3
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NC
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C10, C14
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2
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C1608X7R1H104KT000N
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0.1μF/±10%/50V/X7R
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C-0603
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TDK
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C11
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1
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GRM31CR61A226KE19L
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22μF/10V/X5R
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C-1206
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MURATA
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C15
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1
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GRM31CR71E106KA12L
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10μF/25V/X7R
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C-1206
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MURATA
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L1
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1
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PIFE25201T-R47MS
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0.47μH
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2.5 x 2.0 mm
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CYNTEC
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R24
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1
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65.3kΩ
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R-0603
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R29
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1
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39.2k
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R-0603
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R30
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1
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100k
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R-0603
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R31
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1
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180k
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R-0603
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PCB Layout
Top View
Bottom View