®
RT4531
Dual Channel 10s2p WLED Drivers
General Description
The RT4531 is a dual-channel current source with high-
efficiency asynchronous boost converter for backlight
application. The RT4531 has built-in 1.5A/36V power
MOSFET and two high current-matching capability current
sink, so RT4531 can drives up 10s2p white LED. The
RT4531 can allow very low voltage headroom control,
therefore to improve LED strings efficiency effectively.
The RT4531 supports both PWM dimming and 1-wire
digital dimming interface and it can realize 10 bit
brightness code programming.
The RT4531 provides complete protection functions such
as input Under-Voltage Lockout (UVLO), Over-Current
Protection (OCP), Output Over Voltage (OVP) and Over-
Temperature Protection (OTP).
The RT4531 is available in the WL-CSP-9B 1.35x1.35
(BSC) package.
Features
Input Voltage Range : 2.5V to 5.5V
Internal Soft-Start, UVLO, OTP, OCP, OVP
Typical Shutdown Current : < 1μA
μ
1MHz Switching Frequency
Drives Up to 10 WLEDs in Two Strings
Independent PWM Dimming and 1-Wire Dimming
Control
PWM Dimming Frequency from 20k to 100kHz
Up to 10 Bit Dimming Resolution
LED Current Accuracy
±
2% ( > 5mA)
LED Current Matching
±
2% ( > 5mA)
Built-in IFB1/IFB2 pin OVP, Short Protection, and
Un-Use Detection
Ordering Information
RT4531
Package Type
WSC : WL-CSP-9B 1.35x1.35 (BSC)
Note :
Richtek products are :
½
Applications
Smart Phones
Probable Instruments
Backlight for Small and Media Form
Factor LCD Display with Single-cell Battery Input
RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
½
Simplified Application Circuit
L
V
IN
C1
R1
VIN
C2
EN
PWM
SW
…
…
C3
RT4531
2P10S
WLEDs
Enable
PWM Dimming
IFB1
IFB2
ISET
R2
GND AGND
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS4531-01 July 2016
www.richtek.com
1
RT4531
Pin Configurations
(TOP VIEW)
IFB2
Marking Information
33 : Product Code
33W
A3
B3
C3
W : Date Code
ISET
PWM
EN
A1
B1
C1
A2
B2
IFB1
GND
SW
AGND
C2
WL-CSP-9B 1.35x1.35 (BSC)
Functional Pin Description
Pin No.
A1
A2
A3
B1
B2
B3
C1
C2
C3
Pin Name
ISET
IFB2
IFB1
PWM
AGND
GND
EN
VIN
SW
Pin Function
Full-Scale LED Current Set Pin. Connecting a resistor to the pin programs the
full-scale LED current.
Single Output 2 for Backlight LED.
Single Output 1 for Backlight LED.
Enable Control, and PWM Dimming Signal Input.
Analog Ground.
Power Ground.
Enable Control, and 1-Wire Dimming Signal Input.
Supply Input Pin.
Switch Node of Boost Converter.
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
VIN
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS4531-01 July 2016
RT4531
Function Block Diagram
VIN
UVLO
OSC
OTP
OVP
SW
DC to DC Core
BL
PWM/Drv
GND
AGND
EN
Control
Logic
PWM
Logic
OCP
PWM
FB
OVP
ISET
ISET
Current Source/
FB Short Detect
MINFB
IFB1
IFB2
Operation
The RT4531 is a high efficiency solution with 10S2P string
for backlight applications. The RT4531 optimizes the
feedback regulation voltage to provide high efficiency and
also keep high current matching. The RT4531 can receive
either the 1-wire dimming at EN pin or PWM dimming at
PWM pin for brightness dimming. If the 1-wire dimming is
selected, the PWM pin should be kept high; If the PWM
dimming is selected, the EN pin should be kept high.
OCP Protection
The RT4531 features a 1.5A OCP. The driver provides
cycle-by-cycle current limit function to control the current
on power switch. The boost switch turns off when the
inductor current reaches this current threshold and it
remains off until the beginning of the next switching cycle.
This protects the RT4531 and external component under
overload conditions.
OTP Protection
The OTP function will disable boost and current source
when the junction temperature exceeds 150°C. Then
restart to soft-start when the junction temperature is
smaller than 135°C.
OVP Protection
The OVP function monitors the SW pin's voltage. Once it
exceeds OVP threshold = 36.5V twice, the boost and
current source will be latched off. Until PWM or EN go
high from low again, the latch state will be released.
1-wire Brightness Dimming
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.
PWM Brightness Dimming
Besides programmable built-in 1-wire backlight LED
current control, the RT4531 features a built-in PWM
dimming current control by PWM pin, offering a linear
current dimming by external clock source. In order to
guarantee the PWM dimming resolution, recommending
PWM dimming frequency have to be operated at range of
20kHz to 100kHz.
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS4531-01 July 2016
www.richtek.com
3
RT4531
Absolute Maximum Ratings
(Note 1)
−0.3V
to 6V
38V
−0.3V
to 6V
−0.3V
to 6V
−0.3V
to 6V
1.22W
Supply Voltage, V
IN
-------------------------------------------------------------------------------------------------------
LED Switching Voltage, SW --------------------------------------------------------------------------------------------
LED Current Source Voltage, IFB1, IFB2 ----------------------------------------------------------------------------
Digital Clock Control Pin, EN, PWM ---------------------------------------------------------------------------------
Other Pins, ISET ----------------------------------------------------------------------------------------------------------
Power Dissipation, P
D
@ T
A
= 25°C
WL-CSP-9B 1.35x1.35 (BSC) ------------------------------------------------------------------------------------------
Package Thermal Resistance (Note 2)
WL-CSP-9B 1.35x1.35 (BSC),
θ
JA
------------------------------------------------------------------------------------ 81.5°C/W
Junction Temperature ----------------------------------------------------------------------------------------------------- 150°C
Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------- 260°C
Storage Temperature Range --------------------------------------------------------------------------------------------
−65°C
to 150°C
ESD Susceptibility (Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------------------- 2kV
MM (Machine Model) ----------------------------------------------------------------------------------------------------- 200V
Recommended Operating Conditions
(Note 4)
Supply Input Voltage, V
IN
------------------------------------------------------------------------------------------------ 2.5V to 5.5V
Junction Temperature Range --------------------------------------------------------------------------------------------
−40°C
to 125°C
Ambient Temperature Range --------------------------------------------------------------------------------------------
−40°C
to 85°C
Electrical Characteristics
(V
IN
= 3.6V, C
IN
= 2.2μF, C
OUT
= 1μF, L = 4.7μH, T
A
= 25°C, unless otherwise specified)
Parameter
Power Supply
UVLO
UVLO Hysteresis Voltage
VIN Supply Current
VIN Shutdown Current
Thermal Shutdown
Thermal Shutdown
Hysteresis
Back Light LED
Accuracy of Back Light
Output Current 1/2
Matching of Output Current
Symbol
V
UVLO
V
UVLO
I
Q
I
SHDN
T
SD
Test Conditions
VIN falls
VIN rises after UVLO
EN = High, Non-switching
V
IN
= 5V
Min
--
30
--
--
--
--
Typ
2.2
50
1.2
1
150
15
Max
2.3
200
--
--
--
--
Unit
V
mV
mA
A
C
C
AIBL1, 2
MIBL
I
FBx
= 20mA
I
FBx
= 20mA
I
FBx
= 500A
I
FBx
= 20mA, measured on
IFBx pin which has a lower
voltage.
2
--
--
200
0.88
--
1
1
300
1
2
2
--
430
1.12
%
%
%
mV
MHz
BLED Sense Voltage 1/2
Back Light Switching
Frequency
VDSBL
f
blosc
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS4531-01 July 2016
RT4531
Parameter
Maximum Duty Cycle
Back Light N-MOSFET Ron
Back Light Current Limit
Back Light Over Voltage
Protection
IFBx Pin Over Voltage
Threshold
Logic Control
One Wire Detection Delay
One Wire Detection Time
One Wire Detection Window
Start Time of Program
Stream
End Time of Program
Stream
High Time Low Bit
Low Time Low Bit
High Time High Bit
Low Time High Bit
EN Input
Voltage
PWM Input
Voltage
Logic-Low
Logic-High
Logic-Low
Logic-High
tes_delay
tes_det
tes_win
t
start
t
EOS
t
H_LB
t
L_LB
t
H_HB
t
L_HB
V
EN_L
V
EN_H
V
PWM_L
V
PWM_H
R
EN
R
PWM
T
SD_PWM
T
DS_EN
PWM pin high to low, then
shutdown
EN pin high to low, then
shutdown
Logic 0
Logic 0
Logic 1
Logic 1
Measure from En low to high
En pin low time in detection
window
Measure from En low to high,
Fblosc = 1MHz
300
400
--
3
3
2
2x
tH_LB
2x
tL_HB
2
--
1.4
--
1.4
280
280
20
2.5
--
--
1
--
--
--
--
--
--
--
--
--
--
400
400
--
--
--
--
--
--
--
180
360
360
180
0.4
--
0.4
--
520
520
--
--
s
s
ms
s
s
s
s
s
s
V
Symbol
D
MAX
R
DS(ON)_BLN
I
LIM_BL
V
BLOVP
V
IFBXOVP
After 5ms in soft-start
Close loop, V
IN
= 3.6V
Measure on IFBx pin
Test Conditions
Min
90
100
1.15
35.5
--
Typ
95
270
1.5
36.5
5
Max
--
400
1.85
37.5
--
Unit
%
m
A
V
V
V
k
k
ms
ms
EN Pull Low Resistor
PWM Pull Low Resistor
PWM Logic Low Width to
Shutdown
EN Logic Low Width to
Shutdown
Note 1.
Stresses beyond those listed
“Absolute
Maximum Ratings” may cause permanent damage to the device. These are
stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in
the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may
affect device reliability.
Note 2.
θ
JA
is measured at T
A
= 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7.
Note 3.
Devices are ESD sensitive. Handling precaution is recommended.
Note 4.
The device is not guaranteed to function outside its operating conditions.
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS4531-01 July 2016
www.richtek.com
5
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