RT7251BZQW Evaluation Board Purpose The RT7251B is a high-efficiency current mode synchronous step-down regulator that can deliver up to 1.5A output current from a wide input voltage range of 4V to 17V. This document explains the function and use of the RT7251B evaluation board (EVB) and provides information to enable operation and modification of the evaluation board and circuit to suit individual requirements. Table of Contents Purpose.............................................................................................................................................................. 1 Introduction ........................................................................................................................................................ 2 General Product Information ............................................................................................................................... 2 Key Performance Summary Table ...................................................................................................................... 3 Bench Test Setup Conditions ............................................................................................................................. 4 Headers Description and Placement ................................................................................................................... 4 Test Points ......................................................................................................................................................... 4 Power-up & Measurement Procedure ................................................................................................................. 5 Output Voltage Setting........................................................................................................................................ 5 Schematic, Bill of Materials and Board Layout .................................................................................................... 6 EVB Schematic Diagram .................................................................................................................................... 6 Bill of Materials ................................................................................................................................................... 7 EVB Layout ........................................................................................................................................................ 8 More Information .............................................................................................................................................. 12 Important Notice for Richtek Evaluation Board .................................................................................................. 12 UG7251BZQW-00 April 2014 www.richtek.com RT7251BZQW Evaluation Board Introduction General Product Information General Description The RT7251B is a high efficiency, monolithic synchronous step-down DC/DC converter that operates at 800kHz and delivers up to 1.5A output current from a 4V to 17V input supply. The RT7251B’s current mode architecture allows the transient response to be optimized. Cycle-by-cycle current limit provides protection against shorted outputs and soft-start eliminates input current surge during start-up. Fault conditions also include output under voltage protection, output over voltage protection, and thermal shutdown. The low current (<5μA) shutdown mode provides output disconnect, enabling easy power management in battery-powered systems. The RT7251B is available in a WDFN-8L 2x2 package. Feature 4V to 17V Input Voltage Range 1.5A Output Current Internal N-MOSFETs Current Mode Control Fixed Frequency Operation : 800kHz Output Adjustable from 0.8V to 12V Up to 95% Efficiency Internal Compensation Stable with Low ESR Ceramic Output Capacitors Cycle-by-Cycle Over Current Protection Input Under Voltage Lockout Output Under Voltage Protection Output Over Voltage Protection Power Good Indicator Thermal Shutdown Protection UG7251BZQW-00 April 2014 www.richtek.com 2 RT7251BZQW Evaluation Board Key Performance Summary Table Key features Evaluation board number: PCB005_V1 Default Input Voltage 12V Max Output Current 1.5A Default Output Voltage 3.3V Default Marking & Package Type RT7251BZQW (WDFN-8L 2x2) Operation Frequency Steady 800kHz at all load currents Other Key Features 4V to 17V Input Voltage Range Power Good Indicator Tiny WDFN-8L 2x2 package Protection Over Current Protection Hiccup Mode Output Under-Voltage & Over-Voltage Protection Thermal Shutdown UG7251BZQW-00 April 2014 www.richtek.com 3 RT7251BZQW Evaluation Board 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/ Signal Comment (expected waveforms or voltage levels on test points) VIN Input voltage Input voltage range= 4V to 17V VOUT Output voltage Default output voltage = 3.3V Pin name Output voltage range= 0.8V to 12V (see ‘’ Output Voltage Setting’’ section for changing output voltage level) SW Switching node test point SW waveform EN Enable test point Enable signal. EN is automatically pulled high (by R4) to enable operation. Connect EN low to disable operation. BS Boot strap supply test point Floating supply voltage for the high-side N-MOSFET switch PG Power Good test point Power Good Indicator V1 External Voltage for PG External voltage terminal for PG pull-up voltage. GND Ground Ground UG7251BZQW-00 April 2014 www.richtek.com 4 RT7251BZQW Evaluation Board Power-up & Measurement Procedure 1. Apply a 12V nominal input power supply (4V < VIN < 17V) to the VIN and GND terminals. 2. The EN voltage is pulled to logic high by R4 (100kΩ to VIN) to enable operation. Drive EN high (>2.5V) to enable operation or low (<0.4V) to disable operation. 3. Verify the output voltage (approximately 3.3V) 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 (R1, R2) between VOUT and GND with the midpoint connected to FB. The output is set by the following formula: VOUT = 0.8 x (1 + R1 ) R2 The installed VOUT capacitors (C4, C5) are 22μF, 16V X5R ceramic types. Do not exceed their operating voltage range and consider their voltage coefficient (capacitance vs. bias voltage) and ensure that the capacitance is sufficient to maintain stability and provide sufficient transient response for your application. This can be verified by checking the output transient response as described in the RT7251 IC datasheet. UG7251BZQW-00 April 2014 www.richtek.com 5 RT7251BZQW Evaluation Board Schematic, Bill of Materials and Board Layout EVB Schematic Diagram BS D3 VIN GP1 NF U1 TP3 WDFN-8L 2x2 BOOT VOUT GP3 TP6 SW 10nF 3 C7 L1 SW GND Short GND FB PGOOD 5 6 100k R3 TP5 V1 GND TP1 GND TP2 GND GP2 22uF 22uF 0.1uF 15k R2 C10 NF EN 7,8,9 4 EN TP4 47k R1 R4 C8 NF 0.1uF C3 C2 C1 10uF NF C9 C6 NF R6 100k 10uF CP1 6.8uH C5 VIN 1 C4 2 TP7 PG C1, C2: 10μF/50V/X5R, 1206, TDK C3216X5R1H106K C4, C5: 22μF/16V/X5R, 1210, Murata GRM32ER61C226K L1: 6.8μH TAIYO YUDEN NR8040T6R8N, DCR=25mΩ UG7251BZQW-00 April 2014 www.richtek.com 6 RT7251BZQW Evaluation Board Bill of Materials Reference Qty Part number Description Package Manufacture U1 1 RT7251BZQW DC-DC Converter WDFN-8L 2x2 Richtek C1, C2 2 C3216X5R1H106K160AB 1206 TDK 1210 Murata 0603 Murata 0603 TDK 10μF/±10%/50V/X5R Ceramic Capacitor 22μF/±10%/16V/X5R C4, C5 2 GRM32ER61C226KE20# Ceramic Capacitor 10nF/±10%/50V/X7R C7 1 GRM32MR71H103KA01# Ceramic Capacitor 0.1μF/±10%/50V/X7R C3, C6 2 C1608X7R1H104K080AA Ceramic Capacitor C8, C9, C10 0 Not Installed 0603 L1 1 R1 1 47kΩ/±1%, Resistor 0603 R2 1 15kΩ/±1%, Resistor 0603 R3, R4 1 100kΩ/±1%, Resistor 0603 CP1 1 Short D3, R6 0 Not Installed TP 6 Test Pin GP 4 Golden Pin 6.8uH/3.7A/±30%, UG7251BZQW-00 NR8040T6R8N April 2014 DCR=25mΩ, Inductor 8mmx8mmx4mm TAIYO YUDEN www.richtek.com 7 RT7251BZQW Evaluation Board EVB Layout Top View (1st layer) Bottom View (4th Layer) UG7251BZQW-00 April 2014 www.richtek.com 8 RT7251BZQW Evaluation Board Component Placement Guide—Component Side (1st layer) PCB Layout—Component Side (1st Layer) UG7251BZQW-00 April 2014 www.richtek.com 9 RT7251BZQW Evaluation Board PCB Layout—Inner Side (2nd layer) PCB Layout—Inner Side (3rd layer) UG7251BZQW-00 April 2014 www.richtek.com 10 RT7251BZQW Evaluation Board Component Placement Guide—Bottom Side (4th Layer) PCB Layout—Bottom Side (4th Layer) UG7251BZQW-00 April 2014 www.richtek.com 11 RT7251BZQW Evaluation Board 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 TO BUYER OR USER FOR ANY AND ALL DAMAGES INCLUDING WITHOUT LIMITATION TO DIRECT, INDIRECT, SPECIAL, PUNITIVE OR CONSEQUENTIAL DAMAGES. UG7251BZQW-00 April 2014 www.richtek.com 12