Purpose

The RT8555 is a 36V High Efficiency Boost Converter with I²C Controlled 6-CH LED Driver. This document explains the function and use of the RT8555 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 RT8555 is a high efficiency driver for white LEDs. It is suitable for single/two cell battery input to drive LED light bars which contains six strings in parallel and up to 10 WLEDs per string. The internal current sinks support a maximum of ±2% current mismatching for excellent brightness uniformity in each string of LEDs. To provide enough headroom for current sink operation, the Boost controller monitors the minimum voltage of the feedback pins and regulates an optimized output voltage for power efficiency.

The RT8555 has a wide input voltage operating range from 2.7V to 24V and contains I²C interface for controlling the dimming mode, operating frequency and the LED current. The internal 100mΩ, 36V power switch with current-mode control provides over-current protection. The switching frequency of the RT8555 is adjustable from 300kHz to 2MHz, which allows flexibility between efficiency and component size.

The RT8555 is available in the WL-CSP-20B 1.65 x 2.05 (BSC), with pitch 0.4mm package.

Product Feature

• Wide Operating Input Voltage : 2.7V to 24V
• High Output Voltage : Up to 36V
• Programmable Channel Current : 10mA to 35mA
• Channel Current Regulation with Accuracy ±3% and Matching ±2%
• Dimming Controls
► Direct PWM Dimming up to 20kHz and Minimum On-Time to 400ns
► PWM to Analog Dimming up to 20kHz with 8-bit
• I²C Programs LED Current, Switching Frequency, Dimming Mode
• Switching Frequency : 300kHz to 2MHz
• Current Limit, Over-Temperature Protection and Over-Voltage Protection
• Input Under-Voltage Lockout
• RoHS Compliant and Halogen 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. Connect input power and input ground to VIN and GND test pins respectively.

2. Connect LED ligh bars to VOUT and FB1 ~ FB6 test pins respectively.

3. There is a 3- pin header “EN” for enable control. To use a jumper at “H” option to tie EN test pin to input power VIN for enabling the device. Inversely, to use a jumper at “L” option to tie EN test pin and ground GND for disabling the device.

4. There is a 3- pin header “PWM” for PWM dimming control. To use a jumper at “H” option to tie PWM test pin to input power VIN for PWM = 100% dimming the device. Inversely, to use a jumper at “L” option to tie PWM test pin and ground GND for PWM = 0% dimming the device.

5. Usually use Function Generator to produce PWM signal to PWM dimming RT8555 ILED current.

6. Input PWM frequency about 200Hz ~ 20kHz.

7. For detailed RT8555 function operation, please reference RT8555 datasheet.

Schematic, Bill of Materials & Board Layout

EVB Schematic Diagram

Bill of Materials

EVB Layout

Top View (1^st layer)

PCB Layout—Inner Side (2^nd Layer)

PCB Layout—Inner Side (3^rd Layer)

Bottom View (4^th Layer)