RT2855BHGQW Evaluation Board your power partner. 4A, 18V, 650kHz, ACOT™ Synchronous Step-Down Converter Purpose The RT2855BH is an Advanced Constant On-Time (ACOT™) control architecture step-down converter with the input voltage range from 4.5V to 18V and provides 4A output current. This document explains the function and use of the RT2855BH 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_RT2855BHGQW-00 October 2015 1 http://www.richtek.com RT2855BHGQW Evaluation Board your power partner. Introduction General Product Information The RT2855BH is a high-performance 650kHz 4A step-down regulator with internal power switches and synchronous rectifiers. It features quick transient response using its Advanced Constant On-Time (ACOT™) control architecture that provides stable operation with small ceramic output capacitors and without complicated external compensation, among other benefits. The input voltage range is from 4.5V to 18V and the output is adjustable from 0.765V to 7V. Product Feature Fast Transient Response Steady 650kHz Switching Frequency at all Load 4A Output Current Advanced Constant On-Time (ACOT™) Control Optimized for Ceramic Output Capacitors 4.5V to 18V Input Voltage Range Internal 70mΩ Switch and 30mΩ Synchronous Rectifier 0.765V to 7V Adjustable Output Voltage Externally-adjustable, Pre-biased Compatible Soft-Start Cycle-by-Cycle Current Limit Optional Output Discharge Function Output Over- and Under-voltage Shut-down in Hiccup Mode Input Under Voltage Lockout Thermal Shutdown Key Performance Summary Table Key Features Evaluation Board Number : PCB023_V1 Default Input Voltage 12V Max Output Current 4A Default Output Voltage 1.05V Default Marking & Package Type RT2855BHGQW, WQFN-16 3x3 EVB_RT2855BHGQW-00 October 2015 2 http://www.richtek.com RT2855BHGQW 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. Support 4.5V to18V Input Voltage. Must bypass with a suitable large ceramic capacitor at this pin. EN Enable test point A logic-high enables the converter; a logic-low forces the IC into shutdown mode reducing the supply current to less than 10µA. GND Ground Ground. VCC Internal regulator output VCC supplies power for the internal linear regulator that powers the IC. Connect VIN to the input voltage and bypass to ground with a 0.1µF ceramic capacitor. BOOT Bootstrap supply test point Bootstrap supply for high-side gate driver. Connect a 0.1µF capacitor between BOOT and SW to power the internal gate driver. SW Switch node test point SW is the source of the internal N-channel MOSFET switchand the drain of the internal N-channel MOSFET synchronous rectifier. Connect SW to the inductor with a wide short PCB trace and minimize its area to reduce EMI. VREG5 Internal regulator Connect a 1µF capacitor to GND to stabilize output voltage. SS Soft-start control Connect an external capacitor between this pin and GND to set the soft-start time. PG Open drain power good output PGOOD connects to PGND whenever VFB is less than 90% of its regulation threshold (typical). EVB_RT2855BHGQW-00 October 2015 3 http://www.richtek.com RT2855BHGQW Evaluation Board your power partner. Power-up & Measurement Procedure 1. Apply a 12V nominal input power supply (4.5V < VIN < 18V) to the VIN and GND terminals. 2. Connect JP1 to connect VIN to VCC. Set the jumper at JP2 to connect terminals 2 and 3, connecting EN to VCC to enable operation. 3. Verify the output voltage (approximately 1.05V) between VOUT and GND. 4. Connect an external load up to 4A 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 = 0.765 x (1 + EVB_RT2855BHGQW-00 R2 ) R3 October 2015 4 http://www.richtek.com RT2855BHGQW Evaluation Board your power partner. Schematic, Bill of Materials & Board Layout EVB Schematic Diagram Bill of Materials Reference Qty Part Number Description Package Manufacture U4 1 RT2855BHGQW DC/DC Converter WQFN-16 3x3 RICHTEK C1 1 C2, C5, C6, C8, C12 5 C1608X7R1H104K080AA 0.1μF/±10%/50V/X7R C-0603 TDK C3, C4 2 UMK325BJ106MM 10µF/50V/X7R C-1210 TAIYO YUDEN C7 1 0603B332K500 3.3nF/50V/X7R C-0603 WALSIN C9 1 C3225X5R1E226MT 22µF/25V/X5R C-1210 TDK C10 1 C3225X5R1E226MT 22µF/25V/X5R C-1210 TDK C13 1 NA C14 1 NA L1 1 1.4µH/7A 8 x 8 x 4.2 mm TAIYO YUDEN R1 1 0 R-0603 R2 1 8.25k R-0603 R3 1 22.1k R-0603 R4, R5 2 100k R-0603 R6, R7 2 NA EVB_RT2855BHGQW-00 NC NR8040T1R4N October 2015 5 http://www.richtek.com RT2855BHGQW Evaluation Board your power partner. PCB Layout Top View (1st layer) PCB Layout—Inner Side (2nd Layer) EVB_RT2855BHGQW-00 October 2015 6 http://www.richtek.com RT2855BHGQW Evaluation Board your power partner. PCB Layout—Inner Side (3rd Layer) Bottom View (4th Layer) EVB_RT2855BHGQW-00 October 2015 7 http://www.richtek.com RT2855BHGQW 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_RT2855BHGQW-00 October 2015 8 http://www.richtek.com