®
RT8471
1.2A/1A, Hysteretic, High Brightness LED Driver with
Internal Switch
General Description
The RT8471 is a high efficiency, continuous mode inductive
step-down
converter, designed for driving single or multiple
series connected LEDs from a voltage source higher than
the LED voltage. It operates from an input voltage of 7V to
36V and employs hysteretic control with a high side current
sense resistor to set the constant output current.
The RT8471 includes an output switch and a high side
output current sensing circuit, which uses an external
resistor to set the nominal average output current. LED
brightness control is achieved with PWM dimming from
an analog or PWM input signal.
The RT8471 is available in a small TSOT-23-5 package or
a more thermal efficient SOP-8 (Exposed Pad) and MSOP-
8 (Exposed Pad) packages.
Features
7V to 36V Input Voltage Range
Hysteretic Control with High Side Current Sensing
Internal N-MOSFET with 350mΩ Low R
DS(ON)
Ω
1A Output
Current (For TSOT-23-5 Only)
1.2A Output Current (For SOP-8 (Exposed Pad) and
MSOP-8 (Exposed Pad) Only)
Up to 97% Efficiency
Typical
±
5% LED Current Accuracy
Analog or PWM Control Signal for
LED Dimming
300Hz On-Board Ramp Generator
Input Under Voltage Lockout
Thermal Shutdown Protection
RoHS Compliant and Halogen Free
Applications
Ordering Information
RT8471
Package Type
J5 : TSOT-23-5
SP : SOP-8 (Exposed Pad-Option 1)
FP : MSOP-8 (Exposed Pad)
Lead Plating System
G : Green (Halogen Free and Pb Free)
(for MSOP-8 (Exposed Pad) and
TSOT-23-5 )
Z : ECO (Ecological Element with
Halogen Free and Pb free)
(for SOP-8 (Exposed Pad) Only)
Note :
Richtek products are :
½
Automotive LED Lighting
High Power LED Lighting
Indicator and Emergency Lighting
Architectural Lighting
Low Voltage Industrial Lighting
Signage and Decorative LED Lighting
Marking Information
RT8471GJ5
01= : Product Code
01=DNN
DNN : Date Code
RT8471ZSP
RT8471ZSP : Product Number
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.
RT8471
ZSPYMDNN
YMDNN : Date Code
½
RT8471GFP
0D= : Product Code
0D=YM
DNN
YMDNN : Date Code
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8471-02
December 2013
www.richtek.com
1
RT8471
Pin Configurations
(TOP VIEW)
VIN
5
2
SENSE
4
3
VIN
SENSE
GND
ADJ
2
3
4
8
GND
LX
NC
NC
GND
9
7
6
5
SENSE
GND
GND
ADJ
8
2
3
4
GND
9
7
6
5
VIN
NC
LX
LX
LX GND ADJ
TSOT-23-5
SOP-8 (Exposed Pad)
MSOP-8 (Exposed Pad)
Typical Application Circuit
V
IN
7V to 36V
C
IN
RT8471
VIN
SENSE
optional
R
S
ADJ
GND
LX
L
D
Functional Pin Description
Pin No.
TSO T-23-5
1
SOP-8
(Exposed Pad)
7
MSOP-8
(Exposed Pad)
5, 6
Pin Name
LX
Pin Function
Switch O utput Terminal. Dr ai n of inter nal N-MOSFET.
2
3, 8,
2, 3,
GND
9 (Exposed Pad) 9 (Exposed Pad)
4
4
ADJ
Ground. The exposed pad must be soldered to a
large PCB and connected to GND for maximum
power dissipation.
Dimming Control Input :
--- Analog signal input for analog PWM dimming.
--- PWM signal input for digital PWM dimming.
Output Current Sense. Sense LED string current with
an external resistor connected between VIN and
SENSE.
Supply Input Voltage.
No Internal Connection.
3
4
5
--
2
1
5, 6
1
8
7
SENSE
VIN
NC
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS8471-02
December 2013
RT8471
Function Block Diagram
VIN
Regulator
Bandgap
SENSE
-
+
UVLO
UVLO
V
CC
1.25V
+
-
Ramp Gen.
Dimming
UVLO
Dimming
LX
GND
+
ADJ
-
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8471-02
December 2013
www.richtek.com
3
RT8471
Absolute Maximum Ratings
(Note 1)
−0.3V
to 40V
−0.3V
to (V
IN
+ 0.7V)
(V
IN
−
5V) to (V
IN
+ 0.3V)
−0.3V
to 6V
0.37W
0.43W
Supply Input Voltage, V
IN
-------------------------------------------------------------------------------------
Switch Voltage, LX ---------------------------------------------------------------------------------------------
Sense Voltage, SENSE --------------------------------------------------------------------------------------
All Other Pins -----------------------------------------------------------------------------------------------------
Power Dissipation, P
D
@ T
A
= 25°C
TSOT-23-5 (Two-layer PCB) ----------------------------------------------------------------------------------
TSOT-23-5 (Four-layer PCB) ---------------------------------------------------------------------------------
SOP-8 (Exposed pad, Two-layer PCB) -------------------------------------------------------------------- 2.35W
SOP-8 (Exposed pad, Four-layer PCB) ------------------------------------------------------------------- 3.26W
MSOP-8 (Exposed pad, Two-layer PCB) ----------------------------------------------------------------- 1.38W
MSOP-8 (Exposed pad, Four-layer PCB) ---------------------------------------------------------------- 2.1W
Package Thermal Resistance (Note 2)
TSOT-23-5,
θ
JA
(Two-layer PCB) ---------------------------------------------------------------------------- 264.4°C/W
TSOT-23-5,
θ
JC
(Two-layer PCB) ---------------------------------------------------------------------------- 21.8°C/W
TSOT-23-5,
θ
JA
(Four-layer PCB) --------------------------------------------------------------------------- 230.6°C/W
TSOT-23-5,
θ
JC
(Four-layer PCB) --------------------------------------------------------------------------- 21.8°C/W
SOP-8 (Exposed pad, Two-layer PCB),
θ
JA
--------------------------------------------------------------
SOP-8 (Exposed pad, Two-layer PCB),
θ
JC
--------------------------------------------------------------
SOP-8 (Exposed pad, Four-layer PCB),
θ
JA
-------------------------------------------------------------
SOP-8 (Exposed pad, Four-layer PCB),
θ
JC
-------------------------------------------------------------
MSOP-8 (Exposed pad, Two-layer PCB),
θ
JA
-----------------------------------------------------------
MSOP-8 (Exposed pad, Two-layer PCB),
θ
JC
-----------------------------------------------------------
MSOP-8 (Exposed pad, Four-layer PCB),
θ
JA
----------------------------------------------------------
MSOP-8 (Exposed pad, Four-layer PCB),
θ
JC
----------------------------------------------------------
Junction Temperature ------------------------------------------------------------------------------------------
Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------
Storage Temperature Range ---------------------------------------------------------------------------------
ESD Susceptibility (Note 3)
HBM (Human Body Model) -----------------------------------------------------------------------------------
MM (Machine Model) ------------------------------------------------------------------------------------------
(Note 4)
42.5°C/W
3.4°C/W
30.6°C/W
3.4°C/W
72°C/W
11.9°C/W
47.4°C/W
11.9°C/W
150°C
260°C
−65°C
to 150°C
2kV
200V
Recommended Operating Conditions
Supply Input Voltage, V
IN
------------------------------------------------------------------------------------- 7V to 36V
Junction Temperature Range ---------------------------------------------------------------------------------
−40°C
to 125°C
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS8471-02
December 2013
RT8471
Electrical Characteristics
(V
IN
= 12V, T
A
= 25°C, unless otherwise specified)
Parameter
Mean Current Sense Threshold
Voltage
Sense Threshold Hysteresis
Symbol
V
SENSE
V
SENSE
Test Conditions
Measure on SENSE Pin with
Respecting to V
IN
. ADJ is
Floating.
Min
95
--
Typ
100
±15
350
0.01
5.2
400
300
--
--
--
1.2
0.4
210
170
450
1000
25
300
150
30
Max
105
--
500
10
--
--
--
--
0.2
1.3
1.3
--
--
--
--
--
--
--
--
--
Unit
mV
%
m
A
V
mV
Hz
V
V
V
ns
ns
A
A
ns
nA
C
C
Low Side Switch On-Resistance
R
DS(ON)
Low Side Switch Leakage Current
Under Voltage Lockout Threshold
Under Voltage Lockout Threshold
Hysteresis
Ramp Frequency
ADJ Input Threshold
Voltage
Logic-High
Logic-Low
Logic-High
Logic-Low
t
ON(MIN)
t
OFF(MIN)
I
VIN, Off
I
VIN, On
t
PD
I
SENSE
T
SD
T
SD
V
UVLO
V
UVLO
f
RAMP
V
ADJ, H
V
ADJ, L
V
LX
= 12V, V
ADJ
= 0V
VIN Rising
--
--
--
--
--
1.4
--
0.3
--
0.3
Analog Dimming Range
Analog Dimming
Threshold Voltage
Minimum Switch On-Time
Minimum Switch Off-Time
Quiescent Input Current with
Output Off
Quiescent Input Current with
Output Switching
Internal Propagation Delay
Sense Pin Input Current
Thermal Shutdown
Thermal Shutdown Hysteresis
LX Switch On
LX Switch Off
V
ADJ
= 0V
ADJ is Floating, f
SW
= 250kHz,
V
IN
= 8V
V
SENSE
= V
IN
0.1V
--
--
--
--
--
--
--
--
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 in natural convection at T
A
= 25°C on a two-layer and four-layer test board of JEDEC 51 thermal
measurement standard. For SOP-8 (Exposed Pad) and MSOP-8 (Exposed Pad) the measurement case position of
θ
JC
is on the exposed pad of the package. For TSOT-23-5, the measurement case position of
θ
JC
is on the lead of the
package.
Note 3.
Devices are ESD sensitive. Handling precaution is recommended.
Note 4.
The device is not guaranteed to function outside its operating conditions.
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8471-02
December 2013
www.richtek.com
5
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