®
RT8476
Two-Stage Hysteretic LED Driver Controller
General Description
The RT8476 is a two-stage controller with dual gate drivers
consist of a Boost converter (first stage) and a Buck
converter (second stage). The advantage of the two-stage
topology is highly compatible with ET (Electronic
Transformer) in MR16 / AR111 lighting market field
applications.
The first stage is a Boost converter for constant voltage
output with inductor peak current over current protection.
The second stage is a Buck converter for constant output
current by typical constant peak current regulation.
The RT8476 is equipped with dual output gate drivers for
external power MOSFETs, suitable for higher power
applications.
The RT8476 is available in the SOP-8 and SOP-8 (Exposed
pad) packages.
Features
Two-Stage Topology (Boost + Buck)
Wide Input Voltage Range : 4.5V to 40V
Adjustable Peak Input Current Control
Adjustable Boost Output Voltage
Independent Dual Stage Function
Adjustable LED Current with
±
5% LED Current
Accuracy
Input Under Voltage Lockout Detection
Thermal Shutdown Protection
SOP-8 and SOP-8 (Exposed Pad) Packages
RoHS Compliant and Halogen Free
Ordering Information
RT8476
Package Type
S : SOP-8
SP : SOP-8 (Exposed Pad-Option 2)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
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.
Applications
MR16 Lighting
Signage and Decorative LED Lighting
Architectural Lighting
High Power LED Lighting
Low Voltage Industrial Lighting
Indicator and Emergency Lighting
Automotive LED Lighting
Simplified Application Circuit
L1
D1
VL
AC 12V
VN
D3
D4
R6
D2
D6
C
OUT
R4
RT8476
OVP
VCC
ISN
CREG
LED+
C3
M2
GATE2
GND
D7
L2
C6
LED-
R
SENSE
R5
C
IN
M1
GATE1
CS
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8476-00 April 2013
www.richtek.com
1
RT8476
Marking Information
RT8476GS
RT8476GS : Product Number
Pin Configurations
(TOP VIEW)
GATE1
CS
OVP
GND
2
3
4
8
7
6
5
RT8476
GSYMDNN
YMDNN : Date Code
GATE2
CREG
VCC
ISN
RT8476GSP
RT8476GSP : Product Number
SOP-8
GATE1
CS
OVP
GND
2
3
4
8
RT8476
GSPYMDNN
YMDNN : Date Code
GATE2
CREG
VCC
ISN
7
6
5
GND
9
SOP-8 (Exposed Pad)
Functional Pin Description
Pin No.
SOP-8
1
2
3
4
5
6
7
8
SOP-8
(Exposed Pad)
1
2
3
4,
9 (Exposed Pad)
5
6
7
8
Pin Name
GATE1
CS
OVP
GND
ISN
VCC
CREG
GATE2
Pin Function
Gate Driver Output for External MOSFET Switch in the First Stage.
Current Sense Input for External MOSFET Switch.
Over Voltage Protection Sense Input.
Ground. The exposed pad must be soldered to a large PCB and
connected to GND for maximum power dissipation.
LED Current Sense Amplifier Negative Input.
Supply Voltage Input. For good bypass, place a ceramic capacitor
near the VCC pin.
Internal Regulator Output. Place an 1μF capacitor between the
CREG and GND pins.
Gate Driver Output for External MOSFET Switch in the Second
Stage.
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS8476-00 April 2013
RT8476
Function Block Diagram
ISN VCC
-130mV
V
VCC
-
+
Regulator
CREG
UV
EN2
EN1
EN1
CS
+
-
OVP
Core
Logic
EN2
CREG
GATE2
GATE1
V
240mV
GND
Operation
The VCC of the RT8476 is supplied from the first stage
Boost output. The first stage is a constant output voltage
Boost topology. The CS pin senses the peak inductor
current for over current protection. The peak inductor
current level can be adjusted by the sense resistor
between MOSFET Source and GND pins.
The second stage is a constant output current Buck
topology. The current sense voltage threshold between
the VCC and ISN pins is only 130mV to reduce power
loss.
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8476-00 April 2013
www.richtek.com
3
RT8476
Absolute Maximum Ratings
(Note 1)
Supply Input Voltage, VCC to GND -----------------------------------------------------------------------------------
−0.3V
to 45V
CS, GATE1, GATE2, CREG, OVP to GND --------------------------------------------------------------------------
−0.3V
to 6V
VCC to ISN -----------------------------------------------------------------------------------------------------------------
−1V
to 3V
Power Dissipation, P
D
@ T
A
= 25°C
SOP-8 ------------------------------------------------------------------------------------------------------------------------ 0.53W
SOP-8 (Exposed Pad) --------------------------------------------------------------------------------------------------- 3.44W
Package Thermal Resistance (Note 2)
SOP-8,
θ
JA
------------------------------------------------------------------------------------------------------------------ 188°C/W
SOP-8 (Exposed Pad),
θ
JA
---------------------------------------------------------------------------------------------- 29°C/W
SOP-8 (Exposed Pad),
θ
JC
--------------------------------------------------------------------------------------------- 2°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, VCC ---------------------------------------------------------------------------------------------- 4.5V to 40V
Junction Temperature Range --------------------------------------------------------------------------------------------
−40°C
to 125°C
Ambient Temperature Range --------------------------------------------------------------------------------------------
−40°C
to 85°C
Electrical Characteristics
(V
CC
= 10V, No Load, C
LOAD
= 1nF, T
A
= 25°C, unless otherwise specified)
Parameter
Supply Voltage
CREG UVLO_ ON
CREG UVLO_ OFF
Supply Current
VCC Shutdown Current
VCC Quiescent Current
Internal Reference Voltage
Internal Reference Voltage
Current Sense Comparator
CS Threshold Voltage
CS Pin Leakage Current
Symbol
Test Conditions
Min
Typ
Max
Unit
V
UVOL_ON
V
UVOL_OFF
CS/OVP = 0V
CS/OVP = 0V
4
--
4.3
4.2
4.6
--
V
V
I
SHDN
I
Q
V
CREG
Before Start-Up, V
CC
= 3.5V
After Start-Up, V
CC
= 5V, GATE1
and GATE2 Stand Still
--
--
--
10
1.5
5
4.9
--
--
--
--
μA
mA
V
V
I
CREG
= 20mA
--
V
CS
I
CS
215
--
240
1
265
--
mV
μA
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS8476-00 April 2013
RT8476
Parameter
OVP Threshold
OVP High Level
OVP Low Level
OVP Pin Leakage Current
Gate Driver
GATE1 Duty Off-Time
UGATE1 Drive Sink
LGATE1 Drive Source
GATE1 Default Pull Down Resistor
Buck Converter
ISN Threshold
ISN Hysteresis
ISN Pin Leakage Current
UGATE2 Drive Sink
LGATE2 Drive Source
GATE2 Default Pull Down Resistor
Temperature Protection
Thermal Shutdown Temperature
Thermal Shutdown Hysteresis
T
SD
ΔT
SD
140
--
155
35
170
--
°C
°C
V
ISN
ΔV
ISN
I
ISN
R
UGATE2sk
R
LGATE2sr
Sink = 50mA
Source =
−50mA
123.5
10
--
--
--
--
130
15
1
2
1.25
90
136.5
20
--
--
--
--
mV
%
μA
Ω
Ω
kΩ
R
UGATE1sk
R
LGATE1sr
Sink = 50mA
Source =
−50mA
--
--
--
--
1.5
2
1.25
90
--
--
--
--
μs
Ω
Ω
kΩ
V
OVP_H
V
OVP_L
I
OVP
1.71
1.44
--
1.9
1.6
1
2.09
1.76
--
V
V
μA
Symbol
Test Conditions
Min
Typ
Max
Unit
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
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8476-00 April 2013
www.richtek.com
5
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