RT7255AGV8 Evaluation Board your power partner. 1.5A, 18V, 500kHz ACOT™ Synchronous Step-down Converter Purpose The RT7255 is an Advanced Constant On-Time (ACOT™) mode control synchronous step-down converter with the input voltage range from 4.3V to 18V and provides 1.5A output current. This document explains the function and use of the RT7255 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_RT7255AGV8-00 October 2015 1 http://www.richtek.com RT7255AGV8 Evaluation Board your power partner. Introduction General Product Information The RT7255 is a synchronous step-down converter with Advanced Constant On-Time (ACOT™) mode control. The ACOT™ provides a very fast transient response with few external components. The low impedance internal MOSFET supports high efficiency operation with wide input voltage range from 4.3V to 18V. The proprietary circuit of the RT7255 supports all ceramic capacitors. Product Feature 4.3V to 18V Input Voltage Range Adjustable Soft-Start Time PGOOD Function 1.5A Output Current Advanced Constant On-Time Control Fast Transient Response Support All Ceramic Capacitors Up to 95% Efficiency 500kHz Switching Frequency Adjustable Output Voltage from 0.6V to 8V Cycle-by-Cycle Current Limit Input Under-Voltage Lockout Hiccup Mode Under-Voltage Protection Thermal Shutdown Key Performance Summary Table Key Features Evaluation Board Number : PCB037_V1 Default Input Voltage 12V Max Output Current 1.5A Default Output Voltage 1.2V Default Marking & Package Type RT7255AGV8, SOT-23-8 Operation Frequency Fixed 500kHz EVB_RT7255AGV8-00 October 2015 2 http://www.richtek.com RT7255AGV8 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 [email protected] 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. The input voltage range is from 4.3V to 18V. Must bypass with a suitable large ceramic capacitor at this pin. EN Enable test point Enable control input. Connect EN to a logic-high voltage to enable the IC or to a logic-low voltage to disable. Do not leave this high impedance input unconnected. GND Ground Power ground. Bootstrap supply for high-side gate driver. Connect a 1µF ceramic capacitor between the BOOT and SW pins. BOOT FB Feedback Feedback voltage input. The pin is used to set the output voltage of the converter via a resistive divider. The converter regulates VFB to 0.6V. SW Switch node test point Switch node. PGOOD Power good test point Power good indicator output. SS Soft-start test point Soft-start time setting. Connect a capacitor from SS to GND to set the soft-start period. EVB_RT7255AGV8-00 October 2015 3 http://www.richtek.com RT7255AGV8 Evaluation Board your power partner. Power-up & Measurement Procedure 1. Apply a 12V nominal input power supply (4.3V < VIN < 18V) to the VIN and GND terminals. 2. Set the jumper at JP2 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 1.5A 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 = 0.6 x (1 + EVB_RT7255AGV8-00 R2 ) R3 October 2015 4 http://www.richtek.com RT7255AGV8 Evaluation Board your power partner. Schematic, Bill of Materials & Board Layout EVB Schematic Diagram Bill of Materials Reference Qty Part Number Description Package Manufacture U1 1 RT7255AGV8 DC/DC Converter SOT-23-8 RICHTEK C3 1 GRM31CR71E106KA12L 10μF/25V/X5R C-1206 MURATA C8 1 C1608X7R1H104K080AA 1μF/25V/X5R C-0603 MURATA C4, C6, C10, C11, C12, C1, D2 7 C9 1 22μF/16V/X7R C-1210 MURATA R4, R5 2 10k R-0603 C13 1 10nF/50V/X7R C-0603 R2 1 10k R-0603 R3 1 10k R-0603 L1 1 3.6μH/4.9A 8 x 8 mm EVB_RT7255AGV8-00 N/A GRM32ER61C226KE20L October 2015 0603B103K500 NR8040T3R6N 5 WALSIN TAIYO YUDEN http://www.richtek.com RT7255AGV8 Evaluation Board your power partner. PCB Layout Top View (1st layer) PCB Layout—Inner Side (2nd Layer) EVB_RT7255AGV8-00 October 2015 6 http://www.richtek.com RT7255AGV8 Evaluation Board your power partner. PCB Layout—Inner Side (3rd Layer) Bottom View (4th Layer) EVB_RT7255AGV8-00 October 2015 7 http://www.richtek.com RT7255AGV8 Evaluation Board your power partner. 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. EVB_RT7255AGV8-00 October 2015 8 http://www.richtek.com