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DS8555-01 August 2016www.richtek.com
RT8555
©
Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
Table 12. Brightness Control Table
B
Control2
B
Control1
pwm/26K
Mix Mode
Duty
PWM/I
2
C PWM/MIX ILED Max
PWMO
Duty
Register
MODE
08h[1] 08h[0] 00[7] 00h[3:2] 00h[1] 00h[0]
PWM 0 0 0 Don’t care 0 0 PWMI PWMI
PWM*I
2
C 0 1 0 Don’t care 0 0
PWMI*
04h, 05h
PWMI
I
2
C-PWM-26K 0 0 1 Don’t care 1 0 04h, 05h
04h,
05h
I
2
C-DC-26K 0 0 1 00 1 1 04h, 05h
LED Driver Headroom
The LED driver headroom could be set by the I
2
C, it is shown in the Table 13.
Table 13. LED Driver Headroom
Address Bit Name Default Value Description Resolution R/W
08h [3:2]
LED driver
headroom
B00
LED driver headroom
B00 : 500mV
B01 : 570mV
B10 : 600mV
B11 : 700mV
-- R/W
The RT8555 detects all FBx voltage and selects a minimum voltage to EA (Error Amplifier). When the LED driver
headroom command is below B00, the LED driver headroom will be kept at 500mV and V
OUT
can be boost to the highest
forward voltage of LED strings. This function can guarantee the highest of FB pin voltage is 700mV.
Advanced Brightness Control
Dimming control is received either from PWM input pin or from I
2
C register bits which is shown in the Table 11 below.
Table 11. Advanced Brightness Control
Address Bit Name Default Value Description Resolution R/W
08h [1:0]
Advanced
Brightness
Control
B00
B00 : PWMO = PWMI or I
2
C (04h, 05h)
B01 : PWMO = PWMI multiply I
2
C(04h, 05h)
or I
2
C(04h, 05h)
B10 : PWMO = PWMI multiply I
2
C(06,07h)
or I
2
C(04h, 05h) multiply I
2
C (06, 07h)
B11 : same as B10
R/W
