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RT4530A
6-String 43V White LED Driver with Boost Regulator
General Description
Features
The RT4530A is a high efficiency white LED driver. It is
designed for LCD panel that employs an LED array as the
lighting source. An integrated switch current mode Boost
controller drives six strings in parallel and supports up to
10 pieces of LEDs per string. The internal current sinks
support maximum ±2% current matching for excellent
brightness uniformity in each LED string. To provide enough
headroom for the operating of current sink, Boost controller
monitors the minimum voltage of feedback pins and
regulates an optimized output voltage for power efficiency.

Wide Input Voltage : VIN 2.5V to 24V

High Output Voltage : VOUT up to 43V
Current Mode Boost Regulator
 600kHz to 1.2MHz Switching Frequency
 Up to 85% High Frequency
Adjustable Full Channel Current from 5mA to 50mA
and Matched to 2%
Channel Current Regulation with ±3.5% Accuracy
Dimming Controls
 Direct PWM Dimming up to 20kHz and Minimum
On-Time to 500ns
 PWM to Analog Dimming up to 20kHz with 8 bit
resolution
Built-In Soft-Start to Prevent Inrush Current without
External Capacitor
Disconnects LED in Shutdown
Protection
 Strings Open Detection
 Current Limit Protection
 Adjustable Over-Voltage Protection
 Over-Temperature Protection
20-Lead UQFN Package
RoHS Compliant and Halogen Free




The RT4530A has wide input voltage range from 2.5V to
24V and provides adjustable 5mA to 50mA LED current.
The internal 200mΩ, 43V power switch with current-mode
control provides cycle-by-cycle over-current protection.
The RT4530A also integrates PWM and analog dimming
functions for accurate LED current control. The input PWM
dimming frequency can operate from 100Hz to 20kHz
without inducing any inrush current in LED or inductor.



The RT4530A is available in thin UQFN-20L 3x3 package.
Applications



UMPC and Notebook Computer Backlight
Simplified Application Circuit
D1
L1
VIN
VOUT
COUT
CIN
LX
VIN
Enable
RT4530A OVP
EN
ROVP1
PWM
PWM Signal
COMP
CC
RCOMP
CCOMP
ISET
FREQ
RISET
RFSW
December 2015
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LED1
LED2
LED3
LED4
LED5
LED6
AGND PGND
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DS4530A-00
ROVP2
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RT4530A
Ordering Information
Pin Configurations
RT4530A
COMP
VIN
VDC
PWM
LX
(TOP VIEW)
Package Type
QU : UQFN-20L 3x3 (U-Type)
20 19 18 17 16
Lead Plating System
G : Green (Halogen Free and Pb Free)
EN
FREQ
ISET
MODE
AGND
Note :
Richtek products are :
15
2
14
4
21
5
13
12
11
6
RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.

GND
3
7
8
LX
PGND
PGND
OVP
LED1
9 10
LED6
LED5
LED4
LED3
LED2

1
Suitable for use in SnPb or Pb-free soldering processes.
UQFN-20L 3x3
Marking Information
00= : Product Code
00=YM
DNN
YMDNN : Date Code
Functional Pin Description
Pin No.
Pin Name
Pin Function
Enable Control Input (Active High). There is an internal 400k pull-low
resistor connected to AGND.
1
EN
2
FREQ
3
ISET
4
MODE
Mode Selection Pin. Floating the MODE pin for PWM dimming mode.
Connecting the MODE pin to GND for mixed mode. Connecting the MODE pin
to VDC for pure DC mode.
5
AGND
Analog Ground of LED Driver.
LED6 to LED1
Current Sink for LED String. (Leav e the pin floating or short to GND, if not
used.)
OVP
Over-Voltage Protection for Boost Converter. The detecting threshold is 1.2V.
13, 14
PGND
Power Ground of Boost Converter.
15, 16
LX
The Switching for Boost Converter.
17
PWM
PWM Dimming Control Input.
18
VDC
Internal Regulator Voltage. Connect a capacitor to ground or floating.
19
VIN
Power Supply Input for LED Driver.
20
COMP
Compensation Node for Boost Converter. Connect a compensation network
to ground.
GND
The Exposed Pad must be Soldered to a Large PCB and Connected to GND
for Maximum Power Dissipation.
6, 7, 8, 9, 10, 11
12
21
(Exposed Pad)
Switching Frequency of Boost Converter Setting Input. Connect a resistor to
ground.
LED Current Setting. LED current is set by the value of the resistor RISET
connected from the ISET pin to ground. VISET is typically 1V.
ILED  mA  
1000
RISET  k  
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is a registered trademark of Richtek Technology Corporation.
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December 2015
RT4530A
Function Block Diagram
VIN VDC
OVP
FREQ
+
1.2V
-
OSC
EN
LDO
Q
R
Q
OCP
+
+
PWM
Controller
OTP
PGND
+
COMP
PWMO
Generator
PWM-to-DC
MUX
PWM
S
LX
GND
0.5V
6
Mini LED
Selection
LED Open
Detection
MODE
LED1
LED2
……
DAC
LED6
+
-
+
+
-
-
……
+
-
ISET
AGND
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 3.8V if VIN is higher than 3.8V.
OSC
The switching frequency is adjustable by the external
resistor connected between the FREQ pin and GND.
the LX N-MOSFET will be turned off until the temperature
is lower than the 120°C (typically).
OVP
When the OVP pin voltage is higher than 1.2V, the LX
N-MOSFET is turned off immediately to protect the LX
N-MOSFET.
Minimum LED Selection
PWM Controller
This controller includes some logic circuit to control LX
N-MOSFET on/off. This block controls the minimum ontime and max duty of LX.
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 600mV and
Vout can be Boost to the highest forward voltage of LED
strings.
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. That
OCP > 2.5A and keeps 2ms, IC will be shutdown. When
the junction temperature is higher than 150°C (typically),
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
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December 2015
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.
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RT4530A
Absolute Maximum Ratings










(Note 1)
Supply Input Voltage, VIN to GND -----------------------------------------------------------------------------------EN, PWM, ISET, COMP, MODE, FREQ to GND -----------------------------------------------------------------LX, OVP, LED1 to LED6 to GND --------------------------------------------------------------------------------------VDC to GND ---------------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
−0.3V to 26.5V
−0.3V to 26.5V
−0.3V to 48V
−0.3V to 7V
UQFN−20L 3x3 ------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
UQFN−20L 3x3, θJA ------------------------------------------------------------------------------------------------------UQFN−20L 3x3, θJC -----------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------------------MM (Machine Model) -----------------------------------------------------------------------------------------------------
3.36W
Recommended Operating Conditions



29.7°C/W
12.1°C/W
260°C
150°C
−65°C to 150°C
2kV
200V
(Note 4)
Supply Input Voltage, VIN ----------------------------------------------------------------------------------------------- 2.5V to 24V
Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range -------------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 5V, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
IVIN
PWM = COMP = 0V, Not Switching
--
3
--
IVIN_SW
PWM = COMP = 2V, Switching
--
4
--
VIN Shutdown Current
ISHDN
VIN = 4.5V, EN = 0V
--
--
10
VIN Under-Voltage Lockout
Threshold
VUVLO
VIN Rising
2.1
2.3
2.5
Hysteresis
0.1
0.2
0.3
Logic-High VIH
VIN = 2.5V to 24V
1.3
--
--
Logic-Low
VIN = 2.5V to 24V
--
--
0.7
RfSW = Open
--
0.6
--
RfSW = 110k
--
0.8
--
RfSW = 59k
--
1
--
RfSW = 38.2k
--
1.2
--
VIN > 4.5V
--
0.2
--
VIN Quiescent Current
Unit
mA
A
V
Control Input
EN, PWM, MODE
Input Voltage
VIL
V
Boost Converter
Switching Frequency
LX On-Resistance
(N-MOSFET)
fSW
RLX
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MHz

is a registered trademark of Richtek Technology Corporation.
DS4530A-00
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RT4530A
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Minimum On-Time
TMON
f SW = 1MHz
--
80
--
ns
Maximum Duty
DMAX
f SW = 600kHz
88
91
96
%
LX Current Limit
ILIM
2.2
2.5
2.8
A
Regulated VLEDx
VLEDx
Highest LED String, ILED = 20mA
--
0.5
--
V
ISET = 20mA, MODE = PWM Mode
3
--
3
%
ISET = 20mA, MODE = Mixed Mode,
PWM Duty < 25%
ISET = 20mA, MODE = Mixed Mode,
PWM Duty = 25% to 100%
MODE = Pure DC Mode PWM
Duty = 15% to 100%
ISET = 20mA, MODE = Pure DC Mode PWM
Duty = 5% to 15%
8
--
8
%
5
--
5
%
8
--
8
%
ISET = 20mA, MODE = Pure DC Mode PWM
Duty = 1% to 5%
10
--
10
%
ISET = 20mA, MODE = PWM Mode
2
--
2
%
ISET = 20mA, MODE = Mixed Mode,
PWM Duty < 25%
2
--
2
%
ISET = 20mA, MODE = Mixed Mode & Pure
DC Mode, PWM Duty = 25% to 100%
2
--
2
%
ISET = 20mA, MODE = Pure DC Mode,
PWM Duty = 5% to 25%
2
--
2
%
ISET = 20mA, MODE = Pure DC Mode,
PWM Duty = 1% to 5%
5
--
5
%
VISET
--
1
--
V
OVP Threshold
VOVP
1.16
1.2
1.24
V
OVP Fault Threshold
VOVPF
--
50
--
mV
Thermal Shutdown
Temperature
TSD
--
150
--
C
LED Pin Under-Voltage
Threshold
VLSD
--
0.1
--
V
LED Current Programming
LED Current Accuracy
(ILEDx ISET) / ISET x
100%
Current Balance
Between CSx (ICSx 
IAVG) / IAVG x 100%
ISET Pin Voltage
ILEDA
ILEDM
Fault Protection
Un-Connection
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. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC 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 © 2015 Richtek Technology Corporation. All rights reserved.
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December 2015
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RT4530A
Typical Application Circuit
L1
10µH
VIN
5V to 24V
CIN
4.7µF
REN
10k
Enable
R1
100
C1
1µF
15, 16
LX
19 VIN
1
RPWM
10k
RT4530A OVP 12
17
RCOMP
5.1k
CCOMP
22nF
RISET
49.9k
COVP
EN
MODE
CPWM
10nF
ROVP2
1M
ROVP1
VDC
PWM
LED1
LED2
LED3
LED4
LED5
LED6
20 COMP
CC
VOUT
43V MAX
COUT
4.7µF
CEN
10nF
PWM Signal
D1
SS26
3 ISET
2 FREQ
RFSW
NC
4
18
47pF
:
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CDC
1µF
11
10
9
8
7
6
AGND PGND GND
5
13, 14 21 (Exposed Pad)
Figure 1. For General Application Circuit
L1
10µH
VIN
2.5V to 24V
D1
SS14
R1
100
VAVDD
5V
C1
1µF
REN
10k
Enable
19 VIN
1
RT4530A OVP 12
EN
MODE
VDC
17
CPWM
10nF
PWM Signal
15, 16
LX
PWM
20 COMP
CC
RCOMP
5.1k
CCOMP
22nF
RISET
49.9k
3 ISET
2 FREQ
RFSW
NC
ROVP2
1M
ROVP1
CEN
10nF
RPWM
10k
VOUT
25V MAX
(VOUT depends
on DMAX)
COUT
4.7µF
CIN
4.7µF
LED1
LED2
LED3
LED4
LED5
LED6
4
18
COVP
47pF
:
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CDC
1µF
11
10
9
8
7
6
AGND PGND GND
5
13, 14 21 (Exposed Pad)
Figure 2. For Low Input Voltage Application Circuit
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RT4530A
Typical Operating Characteristics
LED Driver Efficiency
LED Current vs. Input Voltage
100
22
CH1
CH2
CH3
CH4
CH5
CH6
LED Current (mA)
Efficiency (%)
80
60
40
21
20
19
20
VIN = 12V, LEDs = 10S6P, RISET = 49.9kΩ
VIN = 12V, RISET = 49.9kΩ
0
18
0
10
20
30
40
50
60
70
80
90
100
4
8
Dimming Duty (%)
LED Current vs. PWM Duty Cycle
20
24
OVP Threshold Voltage vs. Input Voltage
OVP Threshold Voltage (V)
1.5
16
PWM = 100Hz
PWM = 1kHz
PWM = 10kHz
PWM = 20kHz
12
8
4
1.4
1.3
1.2
1.1
VIN = 12V, RISET = 49.9kΩ
VIN = 12V, RISET = 49.9kΩ
0
1.0
0
20
40
60
80
100
4
8
PWM Duty Cycle (%)
12
16
20
24
Input Voltage (V)
Quiescent Current vs. Input Voltage
LED Current vs. Temperature
2.5
Quiescent Current (mA)
22
LED Current (mA)
16
Input Voltage VIN (V)
20
LED Current (mA)
12
21
20
19
2.3
2.0
1.8
No Switching
VIN = 12V, RISET = 49.9kΩ
1.5
18
-50
-25
0
25
50
75
100
Temperature (C)
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
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December 2015
125
2.5
7.0
11.5
16.0
20.5
25.0
Input Voltage (V)
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RT4530A
Power On from EN
LED Line Transient Response
EN
(5V/Div)
VIN
(5V/Div)
VLED
(20V/Div)
I LED
(10mA/Div)
LX
(20V/Div)
I IN
(500mA/Div)
VIN = 5V to 13V, RISET = 49.9kΩ
Time (50ms/Div)
Time (5ms/Div)
Power On PWM Mode
Power On Mixed Mode1
VIN
(10V/Div)
EN
(5V/Div)
PWM
(5V/Div)
VIN
(10V/Div)
EN
(5V/Div)
I LED
(50mA/Div)
I LED
(100mA/Div)
PWM
(5V/Div)
VIN = 12V, 60 LEDs, RISET = 49.9kΩ
VIN = 12V, 60 LEDs, RISET = 49.9kΩ
Time (10ms/Div)
Time (10ms/Div)
Power On Mixed Mode2
Power On Mixed Mode3
VIN
(10V/Div)
EN
(5V/Div)
VIN
(10V/Div)
EN
(5V/Div)
PWM
(5V/Div)
PWM
(5V/Div)
I LED
(100mA/Div)
I LED
(100mA/Div)
VIN = 12V, 60 LEDs, RISET = 49.9kΩ
Time (10ms/Div)
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VIN = 12V, 60 LEDs, RISET = 49.9kΩ
VIN = 12V, 60 LEDs, RISET = 49.9kΩ
Time (10ms/Div)
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RT4530A
Application Information
The RT4530A is a general purpose 6-CH LED driver capable
of delivering an adjustable 5mA to 50mA LED current. The
IC is a current mode Boost converter integrated with a
43V/2.5A power switch and can cover a wide VIN range
from 2.5V to 24V. The part integrates built-in soft-start
with PWM dimming control provides over voltage, over
temperature and current limit protection features. It also
integrates PWM and mixed mode dimming function for
accurate LED current control. The PWM dimming
frequency can operate from 100Hz to 20kHz without
inducing any inrush current in LED or inductor.
LED Driver Inductor Selection
LED Power Soft-Start Function
IOUT is the sum of current from all LED strings.
The period from EN is enabled to LED current rises, is
several tens of milliseconds according to the brightness
dimming mode (PWM Mode or Mixed Mode). The LED
current starts up after VIN, PWM and EN signals are all
ready. The RT4530A supports soft-start function to reduce
inrush current, and the soft-start inrush peak current must
be less than 2.5A.
The LED Boost converter operates in DCM over the entire
input voltage range when the inductor value L1 is less
than this value L. With an inductance greater than L, the
converter operates in CCM at the minimum input voltage
and may be discontinuous at higher voltages. The inductor
must be selected with saturation current rating greater
than the peak current calculated by the following
equation :
 VOUT  IOUT   VIN  TSW   VOUT  VIN 
IPEAK 



  VIN
 2  L   VOUT

LED Driver Compensation
The control loop can be compensated by adjusting the
external components connected to the COMP pin. The
COMP pin is the output of the internal error amplifier. The
compensation capacitors, CC and CCOMP, will adjust the
zero and pole respectively to maintain stability. Moreover,
the resistor, RCOMP, will adjust the mid-band gain for fast
transient response.
Setting and Regulation of LED Current
The LED current can be calculated by the following
equation :
ILED  1000 (mA)
RISET
where, RISET is the resistor between the ISET pin and
GND. This setting is the reference for the LED current at
LED1 to LED6 and represents the sensed LED current for
each string. The DC/DC converter regulates the LED
current according to the setting.
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The value of the inductor (L) calculated by the following
equation determines the criteria of the transition from DCM
to CCM mode :
L
 VOUT  VIN   VIN2
2  IOUT  fSW  VOUT 2
where,
VOUT is the maximum output voltage.
VIN is the minimum input voltage.
fSW is the switching frequency.
LED Driver Diode Selection
Schottky diode is a good choice for any asynchronous
Boost converter due to its small forward voltage and fast
switching speed. However, when selecting a Schottky
diode, important parameters such as power dissipation,
reverse voltage rating and pulsating peak current must all
be taken into consideration. Choose a suitable diode with
reverse voltage rating greater than the maximum output
voltage.
LED Driver Capacitor Selection
The input capacitor reduces current spikes from the input
supply and minimizes noise injection to the converter. For
most applications, a 4.7μF ceramic capacitor is sufficient.
A value higher or lower may be used depending on the
noise level from the input supply and the input current to
the converter. It is recommended to choose a ceramic
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RT4530A
capacitor based on the output voltage ripple requirements.
The minimum value of the output capacitor, COUT, can be
calculated by the following equation :
COUT 
100% 50%
PWM Mode / Mixed Mode and Pure DC Mode
Brightness Dimming
The RT4530A allows three ways of LED brightness control.
T
OA
Figure 3. LED Current Control Using PWM Dimming
Mode (MODE = Floating)
Duty =
100%
Duty =
90%
Duty =
10%
Duty =
50%
Duty =
100%
Duty =
50%
PWM
100%
ISET
100%
ISET
90%
ISET
50%
ISET
50%
ISET
IOUT
25%
ISET
Figure 4. LED Current Control Using Mixed Dimming
Mode (MODE = GND)
(b) PWM Duty < 25%, the DC dimming will translate to
DC-PWM dimming to control the LED current. In this state,
the LED current is fixed at 0.25 x ISET, and the dimming
duty is 4 x PWM duties.
The minimum D/A converter is 512 steps resolution for
ISET regulation.
T
IOUT
(a) When 25% ≤ PWM duty ≤ 100%, the current source
outputs are DC dimming, and the PWM duty cycle
modulates the amplitude of the currents.
Pure DC Mode Dimming : If the MODE pin is set to VDC,
the PWM and IOUT will delay by two periods. First cycle
delay is required for the period, while the second cycle
delay is for the duty rate calculation.
12.5%
ISET
PWM Mode Dimming : When the MODE pin is set to
float, the dimming mode operates in PWM Mode (Figure
3). During the PWM dimming, the current source turn-on/
off is synchronized with the PWM signal. The LED current
frequency is equivalent to PWM input frequency.
Mixed Mode Dimming : If the MODE pin is set to GND,
the dimming mode operates in Mixed Mode (Figure 4). In
this mode, the PWM and IOUT dimming cycle will delay
by two periods. First cycle delay is required for the period,
while the second cycle delay is for the duty rate
calculation.
25%
PWM
 VOUT  VIN   IOUT
  VRIPPLE  VOUT  fSW
30%
Duty =
100%
Duty =
90%
Duty =
10%
Duty =
50%
Duty =
100%
Duty =
50%
PWM
100%
ISET
100%
ISET
90%
ISET
50%
ISET
50%
ISET
IOUT
10%
ISET
Figure 5. LED Current Control Using Pure DC Dimming
Mode (MODE = VDC)
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DS4530A-00
December 2015
RT4530A
Brightness Control
The RT4530A features the digital dimming control scheme.
A very high contrast ratio true digital PWM dimming can
be achieved by driving PWM pin with a the PWM signal
and the recommended PWM frequency is 100Hz to
10kHz. Dimming frequency can be sufficiently adjusted
from 100Hz to 20kHz. However, LED current cannot be
100% proportional to duty cycle especially for high
frequency and low duty ratio because of physical
limitation caused by inductor rising time. Please refer to
below Table.
VIN
2.3V
UVLO
2.1V
EN
Soft-Start
VOUT
IOUT
Figure 6. LED UVLO Function
Table. Input PWM Dimming Frequency vs Minimum
Duty ( Mixed, PWM and DC Dimming Mode)
VIN
PWM Input Dimming
Frequency
Duty (Min) Duty (Max)
120Hz to 8kHz
0.6%
100%
8.1kHz to 11kHz
0.7%
100%
11.1kHz to 14kHz
0.8%
100%
14.1kHz to 17kHz
0.9%
100%
17.1kHz to 20kHz
1%
100%
Note : The minimum duty in Table is based on the
application circuit and does not consider the deviation of
current linearity when fPWM > 10kHz, ILED may not
achieve setting current in duty (min.) due to different
VOUT / VIN ratio at VIN = 12V.
LED Driver Under Voltage Lockout (UVLO)
The UVLO circuit compares the LED driver input voltage
at VIN with the UVLO threshold (2.3V rising, typ.) to ensure
the input voltage is high enough for reliable operation.
The 200mV (typ.) hysteresis prevents supply transients
from causing a shutdown. Once VIN exceeds the UVLO
rising threshold, the LED soft-start will begin after a delay
time around several milliseconds. When VIN falls below
the UVLO falling threshold, the controller turns off all LED
driver functions.
EN
PWM
VOUT
IOUT
Figure 7. LED Driver Power On Sequence (PWM Mode)
VIN
PWM
EN
Soft-Start
VOUT
ISET x Duty
IOUT
Figure 8. LED Driver Power On Sequence (Mixed Mode)
VIN
PWM
20ms
EN
Soft-Start
VOUT
ISET
Duty x ISET
IOUT
Figure 9. LED Driver Power On Sequence (Mixed Mode;
Duty = 100%)
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS4530A-00
December 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
RT4530A
If at least one channel is in normal operation, the LED
driver will automatically ignore the open channels and
continue to regulate current for the channels in normal
operation.
LED Driver Over Voltage Protection
The LED driver equips an Over Voltage Protection (OVP)
function. When the voltage at the OVP pin reaches a
threshold of approximately 1.2V, the driver will turn off.
The drivers turn on again once the voltage at OVP drops
below the threshold voltage. Thus, the output voltage can
be clamped at a certain voltage level. This voltage level
can be calculated by the following equation :
 R

VOUT, OVP  VOVP   1  OVP2 
 ROVP1 
where ROVP1 and ROVP2 are the resistors in the voltage
divider connected to close to the OVP pin. It is suggested
to use 400kΩ to1MΩ for ROVP2 to reduce loading effect.
Over Temperature Protection
The RT4530A includes an Over Temperature Protection
(OTP) feature to prevent overheating due to excessive
power dissipation from damaging the device. The OTP
function will shut down LED driver when the junction
temperature exceeds 150°C. It will reactivate the device
when powered on again. To maintain continuous operation,
the junction temperature should be kept below 125°C.
Thermal Considerations
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
UQFN-20L 3x3 package, the thermal resistance, θJA, is
29.7°C/W on a standard JEDEC 51-7 four-layer thermal
test board. The maximum power dissipation at TA = 25°C
can be calculated by the following formula :
PD(MAX) = (125°C − 25°C) / (29.7°C/W) = 3.36W for
UQFN-20L 3x3 package
The maximum power dissipation depends on the operating
ambient temperature for fixed T J(MAX) and thermal
resistance, θJA. The derating curve in Figure 10 allows
the designer to see the effect of rising ambient temperature
on the maximum power dissipation.
4.0
Maximum Power Dissipation (W)1
LED Channel Open Circuit Protection
Four-Layer PCB
3.6
3.2
2.8
2.4
2.0
1.6
1.2
0.8
0.4
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 10. Derating Curve of Maximum Power
Dissipation
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and
difference between junction and ambient temperature. The
maximum power dissipation can be calculated by the
following formula :
PD(MAX) = (TJ(MAX) − TA) / θJA
where TJ(MAX) is the maximum junction temperature, TA is
the ambient temperature, and θJA is the junction to ambient
thermal resistance.
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
www.richtek.com
12
is a registered trademark of Richtek Technology Corporation.
DS4530A-00
December 2015
RT4530A
Layout Considerations
PCB layout is very important to design power switching
converter circuits. The following layout guide lines should
be strictly followed for best performance of the RT4530A.

The power components L1, D1, CIN and COUT must be
placed as close as possible to reduce the ac current
loop. The PCB trace between power components must
be short and wide as possible due to large current flow
through these trace during operation.

Place L1 and D1 connected to LX pins as close as
possible. The trace should be short and wide as possible.

It is recommend to place C1 close to VIN pin.

Pin 20 is the compensation point to adjust system
stability. Place the compensation components to pin
20 as close as possible.
Place the power components as
close as possible. The traces
should be wide and short
especially for the high-current loop.
Locate the C1 as close
to VIN as possible.
VIN
GND
CIN
GND
L1
D1
CCOMP
RCOMP
20
19
18
17
COMP
VIN
VDC
PWM
C1
Locate the RISET as close
to ISET as possible.
1
16
COUT
EN
LX
15
PGND 14
2 FREQ
GND
RISET
3
GND
ISET
PGND 13
LED2
LED1 11
LED3
5 AGND
LED4
OVP 12
LED5
4 MODE
LED6
GND
VOUT
R1
LX
The compensation circuit should be
kept away from the power loops and
should be shielded with a ground
trace to prevent any noise coupling.
6
7
8
9
10
Figure 11. PCB Layout Guide
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS4530A-00
December 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
13
RT4530A
Outline Dimension
1
1
2
2
DETAIL A
Pin #1 ID and Tie Bar Mark Options
Note : The configuration of the Pin #1 identifier is optional,
but must be located within the zone indicated.
Symbol
Dimensions In Millimeters
Dimensions In Inches
Min.
Max.
Min.
Max.
A
0.500
0.600
0.020
0.024
A1
0.000
0.050
0.000
0.002
A3
0.100
0.175
0.004
0.007
b
0.150
0.250
0.006
0.010
D
2.900
3.100
0.114
0.122
D2
1.650
1.750
0.065
0.069
E
2.900
3.100
0.114
0.122
E2
1.650
1.750
0.065
0.069
e
L
0.400
0.350
0.016
0.450
0.014
0.018
U-Type 20L QFN 3x3 Package
Richtek Technology Corporation
14F, No. 8, Tai Yuen 1st Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5526789
Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should
obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot
assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be
accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third
parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries.
www.richtek.com
14
DS4530A-00
December 2015