®
RT8406
High Voltage Buck LED Driver with Dimming
Control
General Description
The RT8406 is a current-mode LED driver supporting wide
input voltage range from 10V to 65V. With internal
adjustable operating frequency 65kHz and 130kHz, the
size of the external inductor and input/output capacitors
can be minimized at high operating frequency. High
efficiency is achieved by a 100mV current sensing control.
In addition, the RT8406 features low standby power. LED
dimming control can be done from either analog or PWM
signal and share the same pin. The RT8406 provides
thermal shutdown to prevent the device from overheat.
The RT8406 is available in the SOP-8 package.
Features
Precise and Wide Dimming Range (0.5% to 100%)
Low Standby Power Consumption
High Input Voltage : VIN up to 65V
Current-Mode PWM Control
65kHz/130kHz Adjustable Switching Frequency
Analog and PWM Dimming Control and Share the
Same Pin
Under-Voltage Lockout
Cycle-by-Cycle Current Limitation
Thermal Shutdown
Driver Capability : 350mA /
−
500mA
RoHS Compliant and Halogen Free
Ordering Information
RT8406
Package Type
S : SOP-8
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
½
Applications
DC-DC LED Lighting Driver
Marking Information
RT8406GS : Product Number
RT8406
GSYMDNN
YMDNN : Date Code
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
Pin Configuration
(TOP VIEW)
DIM
VC
CS
GATE
2
3
4
8
7
6
5
VCC
ISN
CREG
GND
SOP-8
Copyright
©
2019 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8406-03 May 2019
www.richtek.com
1
RT8406
Typical Application Circuit
R1
V
IN
C1
RT8406
8
VCC
Analog/PWM
R5
C7
R6
C6
C5
1
DIM
6
CREG
VC
2
C4
GND
5
C3
CS
R4
R3
GATE
3
ISN
7
4
R2
Q1
L1
D1
C2
Suggested Component Values
C3 (nF)
1
C4 (nF)
1
C5 (F)
1
C6 (F)
1
C7 (F)
1
R2 ()
22
R5 ()
51k
R6 ()
510k
Switch Frequency
130kHz
65kHz
R4 (k)
1
2
Functional Pin Description
Pin No.
1
2
3
4
5
6
7
8
Pin Name
DIM
VC
CS
GATE
GND
CREG
ISN
VCC
Pin Function
Analog or PWM dimming control input.
PWM loop compensation node.
MOSFET current sense input.
Gate driver output for external MOSFET switch.
Ground of the controller.
Regulator output.
LED current sense input. Voltage threshold between VCC and ISN is100mV.
Supply voltage input. The controller will be enabled when VDD exceeds V
TH_ON
and
disabled when VDD is lower than V
TH_OFF
.
Copyright
©
2019 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS8406-03 May 2019
RT8406
Functional Block Diagram
VCC
GND
OSC
Regulator
CREG
DIM
Dimming
ISN
CS
Current
Limit
Constant
Current
Control
GATE
VC
Operation
The RT8406 is a current mode PWM controller for Buck
converter applications. With the fixed frequency and
current-mode control scheme, the excellent line and load
regulation can be obtained. Two operating frequencies,
65k and 130k Hz, can be set by the selection of resistance
connected to CS pin. The control loop has a current sense
amplifier which senses the voltage between the VCC and
ISN pins and provides an output voltage at the VC pin. In
normal operation, the GATE turns to high when the gate
driver is set by the oscillator (OSC). Once the sensed
power switch current exceeds the compensated VC pin
voltage, a PWM comparator will reset the gate driver and
then turns off the external power switch. In protection or
abnormal operation, the compensated VC pin voltage could
be pulled low. When the VC voltage is lower than 0.75V
(typ.), the PWM switching signal for GATE will be
terminated.
The current through the sense resistor is set by the signal
at DIM pin and the sense resistance. The voltage across
the sense resistor can be programmed by the analog or
PWM signal on the DIM pin with good dimming linearity.
The Max. current sense threshold voltage (100mV typ.)
can be obtained with DIM pin voltage greater than dimming
high threshold voltage (V
DIM_H
, 2.8V typ.). The sense
threshold is intentionally forced to zero by an internal
comparator when the DIM pin voltage is lower than dimming
disabled voltage (V
DIM_DIS
, 0.25V typ.). When the DIM pin
voltage rises to be higher than dimming enabled voltage
(V
DIM_EN
, 0.3V typ.), the sense threshold turns to positive
and makes GATE turn on.
To reduce the power consumption in shutdown, the RT8406
provides standby mode operation. When the DIM pin
voltage is lower than V
DIM_DIS
and the duration exceeds
1s (typ.), the CREG pin voltage and VC voltage will both
decrease to 0V to disable most control functions. That
means RT8406 enters standby mode. When the DIM pin
voltage rises to be higher than V
DIM_EN
, the GATE will start
to switch after the CREG pin voltage exceeds CREG UV
(6.7V typ.) and VC voltage exceeds 0.75V. That means
RT8406 returns to normal operation.
The RT8406 provides protection functions which include
input voltage under-voltage lockout (UVLO), over-
temperature protection (OTP), and cycle-by-cycle current
limitation to prevent abnormal situations.
Copyright
©
2019 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8406-03 May 2019
www.richtek.com
3
RT8406
Absolute Maximum Ratings
(Note 1)
VCC, ISN to GND ----------------------------------------------------------------------------------------------------------
−0.3V
to 72V
CREG, GATE to GND -----------------------------------------------------------------------------------------------------
−0.3V
to 20V
DIM, VC, CS to GND -----------------------------------------------------------------------------------------------------
−0.3V
to 7.5V
Power Dissipation, P
D
@ T
A
= 25°C
SOP-8 ------------------------------------------------------------------------------------------------------------------------ 0.53W
Package Thermal Resistance (Note 2)
SOP-8,
θ
JA
------------------------------------------------------------------------------------------------------------------ 188°C/W
SOP-8,
θ
JC
------------------------------------------------------------------------------------------------------------------ 47°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
Recommended Operating Conditions
(Note 4)
Supply Input Voltage, VCC ---------------------------------------------------------------------------------------------- 12V to 65V
Junction Temperature Range --------------------------------------------------------------------------------------------
−40°C
to 125°C
Ambient Temperature Range --------------------------------------------------------------------------------------------
−40°C
to 85°C
Electrical Characteristics
(V
CC
= 12V, C
IN
= 1μF, T
A
= 25°C, unless otherwise specified)
Parameter
VCC Section
Rising UVLO Threshold Voltage
Falling UVLO Threshold Voltage
Supply Current
Shutdown Current
Current Sense Section
Input Current of ISN Pin
Mean Current Sense Threshold
Voltage
Current Limit
Dimming Section
Dimming High Threshold
Voltage
Dimming Enabled Voltage
Dimming Disabled Voltage
Symbol
Test Conditions
Min
Typ
Max
Unit
V
TH_ON
V
TH_OFF
I
VCC
I
SD
9
7
--
--
10
8
--
60
11
9
1.2
--
V
V
mA
A
A
mV
mV
I
ISN
VISN = 60V
VCC
ISN
DIM = 3V
--
96
175
30
100
210
--
104
--
V
DIM_H
V
DIM_EN
V
DIM_DIS
--
--
0.19
2.8
0.3
0.25
--
0.35
--
V
V
V
Copyright
©
2019 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS8406-03 May 2019
RT8406
Parameter
Timing Control Section
High Switching Frequency
Low Switching Frequency
Leading Edge Blanking Time
Maximum Duty Ratio
Gate Driving Section
Rising Time
Falling Time
Gate Output Clamping Voltage
Internal Pull Low Resistor
t
R
t
F
V
CLAMP
R
GATE
VCC = 15V, C
L
= 1nF (10%~90%)
VCC = 15V, C
L
= 1nF (90%~10%)
VCC = 15V
VCC = 15V
--
--
8.5
--
40
25
10.25
40
70
50
12
--
ns
ns
V
k
f
SW_H
f
SW_L
t
LEB
D
MAX
R
LP
= 1k, C
LP
= 680pF
R
LP
= 2k, C
LP
= 1nF
110
50
100
94
130
65
150
97
150
80
200
--
kHz
kHz
ns
%
Symbol
Test Conditions
Min
Typ
Max
Unit
Note 1.
Stresses beyond those listed under
“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 under natural convection (still air) at T
A
= 25°C with the component mounted on a high effective-
thermal-conductivity four-layer test board on a JEDEC 51-7 thermal measurement standard.
θ
JC
is measured at the
exposed pad 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
©
2019 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS8406-03 May 2019
www.richtek.com
5
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