Purpose
The RT5710A is a high efficiency synchronous step-down DC-DC converter. Its input voltage range is from 2.5V to 6V and provides an adjustable regulated output voltage from 0.6V to 3.4V while delivering up to 1A of output current. This document explains the function and use of the RT5710A 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 RT5710A is a high efficiency synchronous step-down DC-DC converter. Its input voltage range is from 2.5V to 6V and provides an adjustable regulated output voltage from 0.6V to 3.4V while delivering up to 1A of output current. The internal synchronous low on-resistance power switches increase efficiency and eliminate the need for an external Schottky diode. The Current Mode Constant-On-time (CMCOT) operation with internal compensation allows the transient response to be optimized over a wide range of loads and output capacitors.
Product Feature
- Efficiency Up to 95%
- RDSON 160mΩ HS / 110mΩ LS
- VIN Range 2.5V to 6V
- VREF 0.6V with ±2% Accuracy
- CMCOTTM Control Loop Design for Best Transient Response, Robust Loop Stability with Low-ESR (MLCC) COUT
- Fixed Soft-Start 1.2ms
- Cycle-by-Cycle Over-Current Protection
- Input Under-Voltage Lockout
- Output Under-Voltage Protection (UVP Hiccup)
- Thermal Shutdown Protection
- Power Saving at Light Load
Key Performance Summary Table
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Key Features
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Evaluation Board Number : PCB104_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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1A
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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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RT5710AHGQW, WDFN-6L 2x2
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Operation Frequency
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1.5MHz in CCM mode
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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.
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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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NC, IC
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No Internal Connection
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No internal connection.
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EN
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Enable Control Input
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Enable control input.
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VIN
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Supply Voltage Input
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The RT5710A operates from a 2.5V to 6V input.
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LX
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Switch Node
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Switch node.
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GND
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Ground
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Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum thermal dissipation.
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FB
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Feedback
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Feedback.
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VOUT
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Output Voltage
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Output voltage.
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Power-up & Measurement Procedure
1. Apply a 3.3V nominal input power supply (2.5V < VIN < 6V) to the VIN and GND terminals.
2. Set the jumper at JP1 to connect terminals 2 and 3, connecting EN to VIN through resistor R2 (100kΩ). The Enable pin can connected to VIN directly as well to enable operation.
3. Verify the output voltage (approximately 1.2V) between VOUT and GND.
4. Connect an external load up to 1A 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, R3) between VOUT and GND with the midpoint connected to FB. The output is set by the following formula :
The placement of the resistive divider should be within 5mm of the FB pin. The resistance of R3 is suggested between 10kΩ and 150kΩ to minimize power consumption, and noise pick-up at the FB pin. The resistance of R1 can then be obtained as below :
For better output voltage accuracy, divider resistors (R1 and R3) should have tolerance of ±1% tolerance or better.
Schematic, Bill of Materials & Board Layout
EVB Schematic Diagram
Note :
1. Do not hot-plug a live 3.3V supply to the board; if hot-plugging is required, add ~100µF electrolytic capacitor at the input.
A small feedforward capacitor (C4) can be introduced into the feedback network to speed up the transient response of high output voltage circuits. Adding C4 can also improve the light load PSM switching behavior. The feedforward capacitor is added across the upper FB divider.
To optimize transient response, C4 value is chosen so that the gain and phase boost of the feedback network increases the bandwidth of the converter, while still maintaining an acceptable phase margin. Generally, larger C4 values provide higher bandwidth, but may result in an unacceptable phase margin or instability.
Measurement Results
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Output ripple measurement, 10mA load
Blue : VOUT ; Cyan : V-LX
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Output ripple measurement, 1A load
Blue : VOUT ; Cyan : V-LX
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Output ripple : 24mVpp
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Output ripple : 5.6mVpp, Frequency : 1.519MHz
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Dynamic load 30mA to 800mA
Blue : VOUT ; Green : Load current step
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Dynamic load 300mA to 800mA
Blue: VOUT ; Green : Load current step
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Overshoot : 13mV, undershoot : 30mV
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Overshoot : 13mV, undershoot : 15mV
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OCP measurement : Dynamic load close to OCP
Yellow : VOUT; Blue : Load current step
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OCP measurement : Gradually increase load
Yellow : VOUT; Blue : IOUT
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V-out starts to drop at 1.78A load current
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Auto recovery hiccup mode when OC limit is exceeded.
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Start-up measurement from Enable : EN pin low – high
Green : Enable; Yellow : VOUT; Blue : IOUT
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Start-up measurement from VIN :
Green : VIN; Yellow : VOUT; Blue : IOUT
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Start-up time 1.3msec. Soft-start 1.2msec
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VIN > 2.22V initiates start-up
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Efficiency Measurements
3.3V to 1.2V
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VIN (V)
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VOUT (V)
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IIN (A)
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IOUT (A)
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Efficiency (%)
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3.299
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1.220
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0.0005141
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0.001
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71.93
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3.299
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1.220
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0.00433738
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0.01
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85.26
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3.299
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1.215
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0.04215278
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0.1
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87.37
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3.299
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1.203
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0.12214476
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0.3
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89.56
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3.299
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1.203
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0.20562464
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0.5
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88.67
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3.299
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1.203
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0.33956308
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0.8
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85.91
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3.300
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1.202
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0.43489106
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1
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83.75
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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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Manufacturer
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U1
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1
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RT5710AHGQW
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DC-DC Converter
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WDFN-6L 2x2
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Richtek
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C1, C7
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2
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NC
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C-1206
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C2, C6
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2
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GRM31CR71E106KA12L
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10uF/25V/X7R/1206
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C-1206
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MURATA
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C3
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1
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C1608X7R1H104K080AA
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100nF/50V/X7R/0603
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C-0603
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TDK
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C4, C5
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1
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NC
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C-0603
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L1
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1
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74404042015
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1.5µH
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4.0x4.0x1.8mm
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WURTH ELEKTRONIK
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R1, R2, R3
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3
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100k/0603
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R-0603
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R4
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1
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NC
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R-0603
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PCB Layout
Top View (1st layer)
PCB Layout—Inner Side (2nd Layer)
PCB Layout—Inner Side (3rd Layer)
Bottom View (4th Layer)