RT8498 Step-Down Converter Evaluation Board

Purpose

The RT8498 is specifically designed to be operated in Buck, Boost and Buck-Boost converter applications. This document explains the function and use of the RT8498 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 RT8498 is a current-mode LED driver supporting wide input voltage range from 3V to 18V and output voltage up to 18V. With internal 350kHz operating frequency, the size of the external PWM inductor and input/output capacitors can be minimized. High efficiency is achieved by a 100mV current sensing control. LED dimming control can be done from either analog or PWM signal. The RT8498 provides an internal soft-start function to avoid inrush current and thermal shutdown to prevent the device from overheat. The RT8498 is available in the SOT-23-6 package.

Product Feature

• High Voltage : V_IN Up to 18V, V_OUT Up to 18V
• Built-In 2A Power Switch
• Current-Mode PWM Control
• 350kHz Fixed Switching Frequency
• Analog, PWM Digital or PWM Converting to Analog with One External Capacitor
• Internal Soft-Start to Avoid Inrush Current
• Under-Voltage Lockout
• Internal Over Voltage Protection to Limit Output Voltage
• Cycle-by Cycle Current Limit
• Thermal Shutdown

Key Performance Summary Table

Bench Test Setup Conditions

Headers Description and Placement

Carefully inspect all the components used in the EVB according to the following Bill of Materials table, and then make sure all the components are undamaged and correctly installed. If there is any missing or damaged component, which may occur during transportation, please contact our distributors or e-mail us at 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. Connect input power (4.5V < V_IN < 18V) and input ground to VIN and GND test pins respectively.

2. Connect positive end and negative terminals of load to VOUT2 and VOUT1 test pins respectively..

3. Verify the output voltage/output current (approximately 3.0V/1A) between VOUT2 and VOUT1.

4. V_IN = 12V, V_OUT = 3V, I_OUT = 1A (Buck) ,

LED+ = VOUT2, LED- = VOUT1, LOAD = 1LEDs or Electronic Load CV mode

measure check SW pin freq = 350kHZ , ISP-ISN Threshold = 100mV

LED Current Setting

The LED current can be calculated by the following equation :

where (V_VCC - V_ISN) is the voltage between the VCC and ISN pins (100mV typ. if ACTL dimming is not applied) and

the R_SENSE is the resister between the VCC and ISN pins.

Schematic, Bill of Materials & Board Layout

EVB Schematic Diagram

Bill of Materials

Efficiency:

Line regulation:

Load regulation:

Waveform:

Test condition:VIN = 10V, VOUT = 3V, IOUT = 1A
CH1 = SW, CH2 = VOUT, CH3 = VIN, CH4 = IL	CH1 = SW, CH2 = VOUT, CH3 = VIN, CH4 = IOUT

Analog / PWM Dimming :

PCB Layout

Top View (1^st layer)

Bottom View (4^th Layer)