®
RT8477A
High Voltage High Multiple-Topology Current LED Driver
General Description
The RT8477A is a current mode PWM controller designed
to drive an external MOSFET for high current LED
applications with wide input voltage (4.5V to 50V) and
output voltage (up to 50V) ranges. With internal 380kHz
operating frequency, the size of the external PWM inductor
and input/output capacitors can be minimized. High
efficiency is achieved by a 100mV current sensing control.
LED Dimming control can be done by analog.
The RT8477A is now available in the SOP-8 (Exposed
Pad) package.
Features
Support Multiple-Topologies (Buck/Boost/Buck-
Boost)
High Voltage : V
IN
up to 50V, V
OUT
up to 50V
380kHz Fixed Switching Frequency
Analog or PWM Control Signal for LED Dimming
Internal Soft-Start to Avoid Inrush Current
Under-Voltage Lockout
Thermal Shutdown
Applications
Ordering Information
RT8477A
Package Type
SP : SOP-8 (Exposed Pad-Option 1)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
½
Desk Lights and Room Lighting
Industrial Display Backlight
Pin Configurations
(TOP VIEW)
VCC
ISP
ISN
VC
2
3
4
8
7
CREG
DRV
SENS
CTL
GND
9
6
5
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.
SOP-8 (Exposed Pad)
½
Marking Information
RT8477AGSP : Product Number
RT8477A
GSPYMDNN
YMDNN : Date Code
Simplified Application Circuit
V
IN
C1
R5
RT8477A
VCC
C6
ISN
Analog Dimming
CTL
CREG
C2
GND
DRV
SENS
VC
C5
R3
R4
C3
ISP
R1
D1
C4
LEDs
L1
...
M1
R2
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8477A-03 August 2016
www.richtek.com
1
RT8477A
Functional Pin Description
Pin No.
1
2
3
4
5
6
7
8
9 (Exposed Pad)
Pin Name
VCC
ISP
ISN
VC
CTL
SENS
DRV
CREG
GND
Positive Input Current Sense.
Negative Input Current Sense. Voltage threshold between ISP and ISN is 100mV.
VC Compensation Node for Current Loop.
Analog Dimming Control Input. Effective programming range is 0.33V to 2V.
Current Sense Input for LED Current. Connect the current sense resistor
between external N-MOSFET switch and the ground.
External MOSFET Switch Gate Driver Output.
Regulator Output. Placed 1F capacitor to stabilize the 5V regulator output.
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.
Pin Function
Supply Voltage Input. For good bypass, a low ESR capacitor is required.
Function Block Diagram
OSC
VCC
4.5V
CREG
-
+
S
R
R
DRV
5V
LDO
+
-
VC
Soft-Start
-
GM
+
SENS
ISN
ISP
CTL
+
-
GND
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS8477A-03 August 2016
RT8477A
Operation
The RT8477A is a current mode PWM controller designed
to drive an external MOSFET for high current LED
applications. This device uses a fixed frequency, current-
mode control scheme to provide excellent line and load
regulation.
The control loop has a current sense amplifier which
senses the voltage
between the ISP and ISN pins.
A PWM comparator then turns off the external power
switch when the sensed power switch current exceeds
the internal compensated voltage.
The power switch will
not be reset by the oscillator clock in each cycle. If the
comparator does not turn off the switch in a cycle, the
power switch will be on for more than a full switching period
until the comparator is tripped. In this manner, the
programmed voltage across the sense resistor is regulated
by the control loop.
The current through the sense resistor is set by the
programmed voltage and the sense resistance. The voltage
across the sense resistor can be programmed by the
analog or digital signal at the CTL pin with good dimming
linearity. The max sense threshold of 100mV can be
obtained with CTL pin voltage greater than 2V (max
dimming point). The sense threshold is intentionally forced
to zero by an internal comparator when the CTL pin voltage
is less than around 0.33V (min dimming point). Because
of that, the actual sense threshold right before cut off may
vary from part to part over process variation.
The RT8477A provides protection functions which include
over-temperature, and switch current limit to prevent
abnormal situations.
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8477A-03 August 2016
www.richtek.com
3
RT8477A
Absolute Maximum Ratings
(Note 1)
Supply Input Voltage, VCC ------------------------------------------------------------------------------------
−0.3V
to 60V
ISP, ISN ------------------------------------------------------------------------------------------------------------
−0.3V
to 60V
SENS, DRV, CREG, VC Pin Voltage -----------------------------------------------------------------------
−0.3V
to 5.5V
CTL Pin Voltage -------------------------------------------------------------------------------------------------
−0.3V
to 20V (Note 2)
Power Dissipation, P
D
@ T
A
= 25°C
SOP-8 (Exposed Pad) ----------------------------------------------------------------------------------------- 3.26W
Package Thermal Resistance (Note 3)
SOP-8 (Exposed Pad),
θ
JA
------------------------------------------------------------------------------------ 30.6°C/W
SOP-8 (Exposed Pad),
θ
JC
----------------------------------------------------------------------------------- 3.4°C/W
Junction Temperature ------------------------------------------------------------------------------------------- 150°C
Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------- 260°C
Storage Temperature Range ----------------------------------------------------------------------------------
−65°C
to 150°C
ESD Susceptibility (Note 4)
HBM (Human Body Model) ------------------------------------------------------------------------------------ 2kV
Recommended Operating Conditions
(Note 5)
Supply Input Voltage, VCC ------------------------------------------------------------------------------------ 4.5V to 50V
Junction Temperature Range ----------------------------------------------------------------------------------
−40°C
to 125°C
Ambient Temperature Range ----------------------------------------------------------------------------------
−40°C
to 85°C
Electrical Characteristics
(V
CC
= 12V, T
A
= 25°C, unless otherwise specified)
Parameter
Overall
Regulator Output Voltage
Supply Current
VIN Under Voltage Lockout
Threshold
Current Sense Amplifier
Input Threshold (V
ISP
V
ISN
)
Input Current
Output Current
VC Threshold for CTL Switch Off
LED Dimming
Input Current of CTL Pin
LED Current Off Threshold at CTL
LED Current On Threshold at CTL
Symbol
Test Conditions
Min
Typ
Max
Unit
V
CREG
I
VCC
V
UVLO
I
CREG
= 20mA
V
CTL
= 3V
V
IN
Rising
V
IN
Falling
4.5
Common Mode
20V
4.5
--
--
--
5
--
4.25
4.2
5.5
3
4.5
--
V
mA
V
95
--
--
--
--
100
150
50
10
0.4
105
--
--
--
--
mV
A
A
V
A
V
V
I
ISP
I
ISN
I
VC
V
ISP
= 24V
V
ISN
= 24V
2.4V > VC > 0.3V
I
CTL
V
CTL_OFF
V
CTL_ON
0.2V
V
CTL
1.2V
--
--
--
1
0.33
2
2
0.4
2.5
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS8477A-03 August 2016
RT8477A
Parameter
PWM Converter
Switch Frequency
Maximum Duty Cycle
Minimum On-Time
Gate High Voltage
Gate Driver Source
Gate Driver Sink
Soft-Start Time
Sense Current Limit Threshold
Over-Temperature Protection
Thermal Shutdown Temperature
Thermal Shutdown Hysteresis
T
SD
T
SD
--
--
150
20
--
--
C
C
I
SENS_LIM
(Note 7)
V
GATE_H
I
GATE
= 20mA
f
SW
D
MAX
(Note 6)
330
--
--
4.5
1
1
--
100
380
--
200
5
2.5
3.5
2
150
430
100
--
5.5
--
--
--
--
kHz
%
ns
V
A
A
ms
mV
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.
If connected with a 20kΩ serial resistor, CTL can go up to 40V.
Note 3.
θ
JA
is measured at T
A
= 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7.
θ
JC
is
measured at the exposed pad of the package.
Note 4.
Devices are ESD sensitive. Handling precaution is recommended.
Note 5.
The device is not guaranteed to function outside its operating conditions.
Note 6.
When the natural maximum duty cycle of the switching frequency is reached, the switching cycle will be skipped (not
reset) as the operating condition requires to effectively stretch and achieve higher on cycle than the natural maximum
duty cycle set by the switching frequency.
Note 7.
Guaranteed by design, not subjected to production test.
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8477A-03 August 2016
www.richtek.com
5
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