Purpose
The RT7296A is a current mode step-down converter with the input voltage range from 4.5V to 17V and provides 3A output current. This document explains the function and use of the RT7296A 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 RT7296A is a high-efficiency, 3A current mode synchronous step-down DC/DC converter with a wide input voltage range from 4.5V to 17V. The device integrates 80mΩ high-side and 30mΩ low-side MOSFETs to achieve high efficiency conversion. The current mode control architecture supports fast transient response and internal compensation. A cycle-by-cycle current limit function provides protection against shorted output. The RT7296A provides complete protection functions such as input under-voltage lockout, output under-voltage protection, over-current protection, and thermal shutdown. The PWM frequency is adjustable by the EN/SYNC pin. The RT7296A is available in the TSOT-23-8 (FC) package.
Product Feature
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4.5V to 17V Input Voltage Range
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3A Output Current
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Internal N-Channel MOSFETs
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Current Mode Control
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Fixed Switching Frequency : 500kHz
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Synchronous to External Clock : 200kHz to 2MHz
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Cycle-by-Cycle Current Limit
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TTH Power-Save Mode
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Internal Soft-Start Function
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Input Under-Voltage Lockout
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Output Under-Voltage Protection
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Thermal Shutdown
Key Performance Summary Table
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Key Features
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Evaluation Board Number : PCB040_V1
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Default Input Voltage
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12V
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Max Output Current
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3A
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Default Output Voltage
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3.3V
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Default Marking & Package Type
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RT7296AGJ8F, TSOT-23-8 (FC)
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Operation Frequency
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Steady 500kHz at all loads
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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. Support 4.5V to17V Input Voltage. Must bypass with a suitable large ceramic capacitor at this pin.
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EN/SYNC
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Enable test point
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High = Enable. Apply an external clock to adjust the switching frequency.
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GND
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Ground
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Ground.
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TTH
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Transition threshold
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Connect a resistor divider to let the RT7296A into power saving mode under light loads. Connect to PVCC to force RT7296A into forced PWM mode.
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PVCC
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Internal regulator output
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5V bias supply output. Connect a 0.1µF capacitor to ground.
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BOOT
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Bootstrap supply test point
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Bootstrap supply for high-side gate driver. Connect a 0.1µF ceramic capacitor between the BOOT and SW pins.
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SW
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Switch node test point
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Connect this pin to an external L-C filter.
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Power-up & Measurement Procedure
1. Apply a 12V nominal input power supply (4.5V < VIN < 17V) to the VIN and GND terminals.
2. Set the jumper at JP1 to connect terminals 2 and 3, connecting EN to VIN through resistor R30, to enable operation.
3. Verify the output voltage (approximately 3.3V) between VOUT and GND.
4. Connect an external load up to 3A to the VOUT and GND terminals and verify the output voltage and current.
Output Voltage Setting
Set the output voltage with the resistive divider (R23, R28) 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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RT7296AGJ8F
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DC/DC Converter
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TSOT-23-8 (FC)
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RICHTEK
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C7, C9
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2
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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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C8, C10, C27, C29
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4
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C1608X7R1H104K080AA
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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, C12
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2
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C3225X5R1E226MT
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22µF/25V/X7R
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C-1210
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TDK
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C30
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1
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0603N220J500
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22pF/50V/NPO
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C-0603
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WALSIN
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C31
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1
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NC
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C32
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1
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C1608X5R1E105KT000E
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0.1μF/±10%/25V/X5R
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C-0603
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TDK
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L1
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1
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NR8040T4R7N
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4.7µH/4.1A
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8 x 8 x 4.2 mm
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TAIYO YUDEN
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R23
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1
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40.2k
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R-0603
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R24
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1
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10
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R-0603
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R25
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1
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33k
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R-0603
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R28
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1
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13k
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R-0603
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R29
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1
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10k
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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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91k
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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)