11
DS8555-01 August 2016 www.richtek.com
RT8555
©
Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
The RT8555 is a general purpose 6-CH LED driver and is
capable of delivering a maximum 35mA LED current. The
IC is a current mode Boost converter integrated with a
2.5A power switch and can cover a wide VIN range from
2.7V to 24V and contains I
2
C 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.
Programmable functions include :
PWMO frequencies
LED constant current
Boost switching frequency
Slope for brightness changes
Output Current Resolution
Dithering options
Start-up time
Note : DC mode = Dimming Mode Selection (00h[0] = B1) + Mixed Mode Change Duty = 0% (00h[3:2] = B00)
Address Bit Name Default Value Description R/W
[0] Dimming Mode Selection PWM Mode (B0)
B0 : PWM mode
B1 : Mixed mode
R/W
[3:2] Mixed Mode Change Duty 25% (B11)
B00 : 0%
B01 : 6.25%
B10 : 12.5%
B11 : 25%
R/W 00h
[7] MIX-26K PWM pin (B0)
B0 : follow PWM pin frequency
B1 : fixed 26kHz
R/W
Table 2. Dimming Control Mode Selection
Current limit protection
Over voltage protection
LDO regulation voltage setting
One time programmable (OTP) functions include
0x00~0x03 :
Dimming Control Mode Selection
Dimming Control Signal Selection
Switching Frequency Setting
Current Limit Protection Setting
OVP Voltage Setting
LED Current Setting
LDO Regulation Voltage Setting
ILED Brightness Compensation
Brightness Control by PWM Pin
The RT8555 provide three dimming modes for controlling
the LED brightness. The three dimming modes include
PWM mode, DC mode and Mixed mode, and the dimming
mode could be set by register 00h.
