RT8008GB Evaluation Board

Purpose

The RT8008 is a high-efficiency 1.5MHz current mode synchronous step-down regulator that can deliver up to 600mA output current from an input voltage range of 2.5V to 5.5V. This document explains the function and use of the RT8008 evaluation board (EVB) and provides information to enable operation and modification of the evaluation board and circuit to suit individual requirements.

Introduction

General Product Information

The RT8008 is a high-efficiency pulse-width-modulated (PWM) step-down DC/DC converter. Capable of delivering 600mA output current over an input voltage range of 2.5V to 5.5V, the RT8008 is ideally suited for portable electronic devices that are powered from 1-cell Li-ion battery (or from other power sources within that range) such as cellular phones, PDAs and handy-terminals.

An internal synchronous rectifier with low R_DS(ON) dramatically reduces conduction losses in PWM mode. No external Schottky diode is required in practical applications. The RT8008 automatically turns off the synchronous rectifier when the inductor current is low entering discontinuous PFM mode to increase efficiency at light loads.

The RT8008 enters Low-Dropout mode when normal PWM operation cannot regulate the output voltage, turning on the upper P-MOSFET continuously. The RT8008 enters shutdown mode and consumes less than 0.1μA when EN pin is pulled low.

The switching ripple is easily smoothed-out by small sized filtering elements due to a fixed operating frequency of 1.5MHz. This, along with its small SOT-23-5 and TSOT-23-5 packages provides a small PCB area. Other features include soft start, low internal reference voltage with 2% accuracy, over temperature protection, and over current protection.

Product Feature

• 2.5V to 5.5V Input Range
• Adjustable Output from 0.6V to VIN
• 1.0V, 1.2V, 1.5V, 1.8V, 2.5V and 3.3V Fixed/ Adjustable Output Voltage
• 600mA Output Current, 1A Peak Current
• 95% Efficiency
• No Schottky Diode Required
• 1.5MHz Fixed Frequency at PWM Operation
• Small SOT-23-5 and TSOT-23-5 Package
• RoHS Compliant and 100% Lead (Pb)-Free

Key Performance Summary Table

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.

Power-up & Measurement Procedure

1.Apply a 5V nominal input power supply (2.5V < V_IN < 5.5V) to the VIN and GND terminals.

2.Place a shorting block across pins 1 and 2 of the J1 jumper to connect EN to VIN (>1.5V), to turn on the converter. Short pins 2-3, connecting EN to GND, to turn off the converter.

3.Verify the output voltage (approximately 1.2V) between VOUT and GND.

4.Connect an external load up to 600mA 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:

The installed VOUT capacitor (C4) is a 10μF, 6.3V X5R ceramic type. For higher output voltages, consider its 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 RT8008 IC datasheet.

Schematic, Bill of Materials and Board Layout

EVB Schematic Diagram

C3: 4.7μF/6.3V/X5R, 0603, TDK C2012X5R0J475M

C4: 10μF/6.3V/X5R, 0805, TDK C2012X5R0J106M

L1: 2.2μH TAIYO YUDEN NR3015T2R2M, DCR=60mΩ

Bill of Materials

EVB Layout

Top View (1^stlayer)

Bottom View (2^nd Layer)

Component Placement Guide—Component Side (1^stlayer)

PCB Layout—Component Side (1^stLayer)

Component Placement Guide—Bottom Side (2^nd Layer)

PCB Layout—Bottom Side (2^nd layer)