RT4531
LED Current Setting
DAC code
1024
I
I
(2)
FBX
FB
The dual channels of the RT4531 can provide up to 20 mA
current each.
Where :
No matter either 1-wire Brightness Dimming or PWM
Brightness Dimming is selected, the full-scale current
(current when dimming duty cycle is 100%) of each
channel should be programmed by an external resistor
RISET at ISET pin according to Equation 1.
IFB : the full-scale LED current set by the RISET at ISET
pin.
Code : the 10-bit DAC code D1~D10 programmed by 1-
wire interface.
To enter 1-wire dimming mode, the following digital pattern
on the EN pin must be recognized by the IC when the IC
starts from the shutdown mode.
V
ISET
IFB
KISET
(1)
RISET
Where :
1. Pull the ENpin high to enable the RT4531 and start the
detection window for digital dimming.
VISET = 1V,
KISET = 1268
2. After the digital dimming detection delay time (T-
es_delay, >300μs), drive the EN low for more than the
detection time (T-es_det, >400μs).
Brightness Control
a. 1-wire Brightness Dimming
3. Pull the EN pin high after the detection time (>400μs)
The RT4531 is built-in a 10-bit resolution brightness
control. The EN pin features a simple 1-wire interface to
allow digital brightness control. If the 1-wire dimming is
needed, signals of a specific pattern should be input
detection window into EN pin; Otherwise, PWM pin need
to be enabled.(refer to Timing Diagram1 for Continuous
Coding).The Register Program and register map give an
overview of the protocol used by RT4531.By the 1-wire
BrightnessDimming, a master can program the 10-bit code
D1(LSB) to D10(MSB) to any of 1024 steps with a single
command. The programmed value will be stored in an
internal register and set the dual-channel current according
to Equation 2. The code will be reset to default value when
the IC is shut down or disabled.
and before the detection window (Tes_win, <1.23ms), once
the above 3 conditions are met, the IC immediately enters
the 1-wire dimming mode. The digital dimming
communication can start before the detection window
expires. Once the dimming mode is selected, it cannot
be changed without another start up. This means the IC
needs to be shut down by pulling the EN low for 2.5ms
and restarts. See the dimming mode detection and soft-
start for a graphical explanation. (see TimingDiagram1 for
1-wire Continuous Coding).
L1
4.7µH
D1
V
IN
2.5V to 5.5V
C1
1µF
C3
1µF / 50V
R1
10
SW
VIN
C2
1µF
RT4531
2P10S
WLEDs
PWM
EN
IFB1
IFB2
ISET
1-wire interface
GND AGND
R2
63.4k
Figure 1. RT4531 1-wireDimming TypicalApplication
Copyright 2016 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS4531-01 July 2016
www.richtek.com
10
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