®
RT8555
36V High Efficiency Boost Converter with I
2
C Controlled
6-CH LED Driver
General Description
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 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.
The RT8555 is available in the WL-CSP-20B 1.65 x 2.05
(BSC), with pitch 0.4mm package.
Features
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
½
Direct PWM Dimming up to 20kHz and Minimum
½
On-Time to 400ns
PWM to Analog Dimming up to 20kHz with 8-bit
Resolution
I
2
C Programs LED Current, Switching Frequency,
Dimming Mode
Embedded Memory by OTP
Switching Frequency : 300kHz to 2MHz
Protections
½
LED Strings Open Detection
½
Current Limit
½
Programmable Over Voltage Protection
½
Over-Temperature Protection
20-Ball WL-CSP, with pitch 0.4mm Package
RoHS Compliant and Halogen Free
Ordering Information
RT8555
Package Type
WSC : WL-CSP-20B 1.65x2.05 (BSC)
Note :
Richtek products are :
½
Applications
Tablet and Notebook Backlight
Pin Configuration
(TOP VIEW)
A1
A2
A3
A4
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.
LX PGND SDA SCL
B1
B2
B3
B4
½
LX PGND PWM EN
C1
C2
C3
C4
Marking Information
1X : Product Code
VIN VOUT GND FB3
D1
D2
D3
D4
VIN VCP GND FB2
E1
E2
E3
E4
1XW
W : Date Code
FB6 FB5
FB4
FB1
WL-CSP-20B 1.65 x 2.05 (BSC)
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8555-01 August 2016
www.richtek.com
1
RT8555
Functional Pin Description
Pin No.
A1, B1
A2, B2
A3
A4
B3
B4
C1, D1
C2
C3, D3
C4
D2
D4
E1
E2
E3
E4
Pin Name.
LX
PGND
SDA
SCL
PWM
EN
VIN
VOUT
GND
FB3
VCP
FB2
FB6
FB5
FB4
FB1
Switch node of boost converter.
Power ground.
Data signal input of I
2
C interface.
Clock signal input of I
2
C interface.
PWM dimming control input.
Enable control input (Active High).
Power input.
Output of boost converter.
Ground.
Current sink for LED3.
Output of internal regulator.
Current sink for LED2.
Current sink for LED6.
Current sink for LED5.
Current sink for LED4.
Current sink for LED1.
Pin Function
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS8555-01 August 2016
RT8555
Functional Block Diagram
VIN
VCP
EN
VOUT
1.2V
LDO
-
+
OSC
S
R
Q
Q
LX
OTP
PWM
Controller
+
-
+
+
-
OCP
PGND
V
DS
Mini LED
Selection
LED Open
Detection
6
MUX
PWM
SDA
SCL
I C
2
>
DAC
FB1
FB2
FB6
+
-
+
-
+
-
……
+
-
……
GND
Operation
Enable Control
When VIN is higher than the UVLO voltage and the EN pin
input voltage is higher than rising threshold, the VDC will
be regulated around 3.2V if VIN is higher than 3.2V.
Switching Frequency
The LED driver switching frequency is adjusted by the
I
2
C. The switching frequency is from 300kHz to 1.9MHz.
PWM Controller
This controller includes some logic circuit to control LX
N-MOSFET on/off. This block controls the minimum on-
time and max duty of LX.
OCP & OTP
When LX N-MOSFET peak current is higher than
2.5A(typically), the LX N-MOSFET is turned off
immediately and resumed again at next clock pulse. When
the junction temperature is higher than 150°C (typically),
the LX N-MOSFET will be turned off until the temperature
is lower than the 130°C (typically).
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
OVP
The RT8555 integrates over voltage protection. The over
voltage protection could be set by the I
2
C, When the OVP
pin voltage is higher than 36V, the LX N-MOSFET is turned
off immediately to protect the LX N-MOSFET.
Minimum LED Selection
This block detects all LEDx voltage and select a minimum
voltage to EA (Error Amplifier). This function can guarantee
the lowest of the LED pin voltage is around 500mV and
Vout can be Boost to the highest forward voltage of LED
strings.
LED Open Detection
If the voltage at LEDx pin is lower than 100mV, this
channel is defined as open channel and the Minimum LED
Selection function will discard it to regulate other used
channels in proper voltage.
is a registered trademark of Richtek Technology Corporation.
DS8555-01 August 2016
www.richtek.com
3
RT8555
Absolute Maximum Ratings
(Note 1)
−0.3V
to 26.4V
−0.3V
to 40V
−0.3V
to 6V
2.72W
36.7°C/W
Supply Voltage, VIN to GND ---------------------------------------------------------------------------------------------
LX, VOUT, FB1, FB2, FB3, FB4, FB5, FB6 to GND ---------------------------------------------------------------
EN, PWM, SDA, SCL, VCP to GND -----------------------------------------------------------------------------------
Power Dissipation, P
D
@ T
A
= 25°C
WL-CSP-20B 1.65 x 2.05 (BSC) ---------------------------------------------------------------------------------------
Package Thermal Resistance (Note 2)
WL-CSP-20B 1.65 x 2.05 (BSC),
θ
JA
----------------------------------------------------------------------------------
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
(Note 4)
Recommended Operating Conditions
Junction Temperature Range ---------------------------------------------------------------------------------------------
−40°C
to 125°C
Ambient Temperature Range ---------------------------------------------------------------------------------------------
−40°C
to 85°C
Electrical Characteristics
(V
IN
= 3.8V, C
IN
= 1μF, T
A
= 25°C, unless otherwise specified)
Parameter
Input Power Supply
Input Supply Voltage
Quiescent Current
Shutdown Current
Under-Voltage Lockout Threshold
Under-Voltage Lockout Hysteresis
Over-Temperature Protection
Threshold
Over-Temperature Protection
Hysteresis
Interface Characteristic
EN, PWM, SCL, SDA
Input Voltage
Logic-High
Logic-Low
Symbol
V
IN
I
Q
I
SHDN
V
UVLO
V
UVLO
T
OTP
T
OTP_HYS
Test Conditions
Min
2.7
Typ
3.8
2.7
--
2.3
200
150
20
Max
24
--
1
--
--
--
--
Unit
V
mA
A
V
mV
C
C
LX no switching
V
IN
= 3.8V, EN = 0V
V
IN
Rising
--
--
--
--
--
--
V
IH
V
IL
I
IH_1
I
IH_2
V
OL
I
LK_DIO
External Pull High Current = 3mA
SDA Pin Voltage = 3.3V
1.4
--
--
--
--
--
--
--
--
0.01
0.3
--
--
0.8
10
1
0.5
1
V
V
A
A
V
A
Internal Pull-Low Current for EN,
PWM
Internal Pull-Low Current for SCL,
SDA
Output Low Level for SDA
Output Leakage Current for SDA
I
2
C Interface Timing
Maximum I
2
C Clock Frequency
f
SC_MAX
--
400
--
kHz
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS8555-01 August 2016
RT8555
Parameter
Hold Time for START And
Repeated START Condition
SCL Clock Low Time
SCL Clock High Time
Setup Time for A Repeated
START Condition
SDA Data Hold Time
SDA Data Setup Time
Rising Time of SDA, SCL
Falling Time of SDA, SCL
Setup Time for STOP Condition
I
2
C Bus Free Time Between a
STOP and a START
Capacitive Load for I
2
C Bus
Boost Converter
Switching Frequency Accuracy
Switching Frequency Setting
Range
Maximum Duty Cycle
Boost Switch R
DS(ON)
Switching Current Limitation
LED Current
Leakage Current of FBx
Maximum LED Current Setting
Minimum LED Current Setting
LED Current Accuracy
LED Current Matching
FBx Channel Unused Threshold
Light Bar Open Threshold
PWM Minimum On Duty
I
LK_FB
I
FB(MAX)
I
FB(MIN)
I
FB_ACC
I
FB_MAT
V
FB_UNUSE
V
FB_OPEN
D
PWM_MIN
PWM Dimming Frequency = 20kHz
V
FBx
= 36V, I
FBx
= 0mA
I
FBx
= 20mA
LED 100% Setting
Setting By Dimming
PWM Duty = 100%, I
FBx
= 20mA
PWM Duty = 100%, I
FBx
= 20mA
--
0.3
10
0.2
3
2
--
--
0.8
--
--
--
--
--
--
0.1
0.1
--
1
--
35
--
3
2
--
--
--
A
V
mA
mA
%
%
V
V
%
Minimum FBx Regulation Voltage V
FB(MIN)
f
SW_ACC
f
SW_RG
D
MAX
R
DS(ON)
I
OCP
Boost Operates at PWM Mode,
f
SW
= 600kHz
Boost Operates at PWM Mode
f
SW
= 600kHz
10
0.3
--
--
2
--
--
95
0.1
2.5
10
2
--
0.3
3
%
MHz
%
A
Symbol
t
HD,STA
t
LOW
t
HIGH
t
SU,STA
t
HD,DAT
t
SU,DAT
t
R
t
F
t
SU,STO
t
BUF
C
B
Test Conditions
Min
0.6
1.3
600
600
50
100
--
--
600
1.3
--
Typ
--
--
--
--
--
--
--
--
--
--
--
Max
--
--
--
--
--
--
300
300
--
--
400
Unit
s
s
ns
ns
ns
ns
ns
ns
ns
s
pF
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.
DS8555-01 August 2016
www.richtek.com
5
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