DS4501A 00

®
RT4501/A
High Efficiency Backlight LED Driver
General Description
Features
The RT4501/A is a high-efficiency LED driver for backlight
applications. An asynchronous boost converter with an
internal Schottky diode and a current source driver are
designed to support 6LED/channel with wide input voltage
range from 2.5V to 5.5V.

Input Voltage Range : 2.5V to 5.5V

An I2C interface can provide easy backlight control in fast

Internal Schottky Diode
Fast-speed mode I2C Compatible Interface
Drive Up to 7 WLEDs in 2 String
External PWM/Pulse Brightness Control
550k/1.1MHz Switching Frequency
Built-in Internal Soft-Start
PWM Dimming/Pulse Dimming Resolution 256/128
Steps
I 2 C Programmable 256 Steps Linear Current
Regulation
Up to 85% Efficiency with Small Magnetics
Programmable 16V/25.5V OVP
Current Accuracy ±5% and Current Balance ±3%
UVLO, OVP, OCP, OTP Protection
Shutdown Current : < 1μ
μA
Temperature Range : −40°°C to 85°°C
RoHS Compliant and Halogen Free
and high speed mode. The RT4501 supports linear
mappings with 256 steps to setup the brightness of
backlight LEDs. It also supports PWM dimming to adjust
the brightness.
For brightness dimming, the RT4501A supports 128 steps
pulse dimming which determines the LED current, and
RT4501 support 256 steps PWM dimming which
determines the LED current.
The RT4501/A provides complete protection functions such
as input under-voltage lockout, over-current, output overvoltage and over-temperature protection. The OVP
threshold voltage can be set at 16V and 25.5V for different
applications. The RT4501/A is available in the
WL-CSP-10B 0.87x2.07 (BSC) package.
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Applications

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Cellular Phones
Digital Cameras
PDAs and Smart Phones
Portable Instruments
Simplified Application Circuit
RT4501/A
L
LX
VOUT
COUT
VIN
VOUT
VIN
CIN
Enable
EN
PWM
SCL
SDA
GND
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
DS4501/A-00
September 2014
FB1
FB2
is a registered trademark of Richtek Technology Corporation.
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1
RT4501/A
Pin Configurations
Ordering Information
(TOP VIEW)
RT4501/A
Package Type
WSC : WL-CSP-10B 0.87x2.07 (BSC)
RT4501 : PWM Dimming
RT4501A : Pulse Dimming
Note :
Richtek products are :

RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.

Suitable for use in SnPb or Pb-free soldering processes.
LX
A1
A2
GND
VOUT
B1
B2
VIN
PWM
C1
C2
EN
SDA
D1
D2
SCL
FB2
E1
E2
FB1
WL-CSP-10B 0.87x2.07(BSC)
Marking Information
RT4501WSC
RT4501AWSC
1T : Product Code
28 : Product Code
W : Date Code
1TW
28W
W : Date Code
Functional Pin Description
Pin No.
Pin Name
Pin Function
A1
LX
Switch Node of Boost Converter. Connect an inductor between LX and
VIN.
A2
GND
Ground.
B1
VOUT
Power Output of the Asynchronous Boost Converter for Backlight LEDs.
Connect a 1F or larger ceramic capacitor from VOUT to ground.
B2
VIN
Power Input. Connect this pin to the input power supply voltage.
Connect a 10F or larger ceramic capacitor from the VIN to ground.
C1
PWM
C2
EN
D1
SDA
I2C Serial Data Input/Output. An external pull-up resistor is required.
D2
SCL
I2C Serial Clock Input. An external pull-up resistor is required.
E1
FB2
Single Output 2 for Backlight LED.
E2
FB1
Single Output 1 for Backlight LED.
PWM Dimming Input for Backlight LED.
Enable Control Input (Active High). The chip is in shutdown mode when
the EN pin is low.
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is a registered trademark of Richtek Technology Corporation.
DS4501/A-00
September 2014
RT4501/A
Function Block Diagram
VIN
FB1
Current
Source Gen.
PWM2DC
PWM
VREF
Digital
Control
SDA
EN
LEDs
OTP
VFB
EA
SCL
LX
FB2
OVP
VOUT
+
-
PWM
Logic
VSLOPE
OCP
GND
Operation Description
The RT4501/A is a high efficiency solution with 14 WLEDs
in 2 parallels 7 series for backlight applications. The
RT4501/A optimizes the feedback regulation voltage to
provide up to 85% high efficiency with as high as 8bits
resolution application.
OCP Protection
Linear Brightness Dimming
OTP Protection
2
The RT4501/A features a 1A current limitation. Once
detecting current level over current limitation, the
RT4501/A's LX witching will be forced off to avoid large
current damage.
The RT4501/A is built-in a I C 8-bit resolution brightness
control with maximum 20mA/30mA selection.
Reg0x02<3> corresponds to full-scale LED current control.
Reg0x04 sets 8bits resolution brightness dimming.
The over-temperature protection function will be latched
at shutdown status when the junction temperature
exceeds 150°C for 2ms. After re-power on sequence, the
converter will automatically resume switching.
PWM Brightness Dimming
OVP Protection
2
Besides programmable built-in I C backlight LED current
control, the RT4501 features a built-in PWM dimming
current control by setting Reg0x02<6> to 1, offering a
linear current dimming by external clock source. In order
to guarantee the PWM dimming resolution, recommending
dimming frequency have to be operated at range of 400Hz
to 20kHz.
The over-voltage protection function monitors the output
voltage via the VOUT pin voltage. The OVP threshold
voltage is 25.5V/16V by selection Reg0x02<7>, Once the
LED is open, the output voltage will be limited at OVP
protection level to avoid device breakdown. RT4501 is
shunt-down latched, by triggering OVP event over 40 times.
Pulse Brightness Dimming
The EN pin features a simple digital interface to allow
digital brightness control. Using the one-wire dimming
brightness control can achieve as high as 128 steps
resolution, recommending dimming pulse is larger than
0.2μs. RT4501/A keeps shunt down status, when EN pin
is pulled low keeping 1ms.
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
DS4501/A-00
September 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
3
RT4501/A
Absolute Maximum Ratings
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

(Note 1)
Supply Input Voltage, VIN ----------------------------------------------------------------------------------------------Boost Output Voltage, VOUT ------------------------------------------------------------------------------------------Switching Voltage, LX ---------------------------------------------------------------------------------------------------Current Source Voltage, FB1, FB2 -----------------------------------------------------------------------------------Other Pins, EN, PWM, SCL, SDA -----------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
−0.3V to 6V
−0.3V to 27V
−0.3V to 27V
−0.3V to 27V
−0.3V to 6V
WL-CSP-10B 0.87X2.07 (BSC) ---------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
WL-CSP-10B 0.87x2.07 (BSC), θJA ---------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------------------MM (Machine Model) -----------------------------------------------------------------------------------------------------
1W
Recommended Operating Conditions



99.6°C/W
260°C
150°C
−65°C to 150°C
2kV
200V
(Note 4)
Supply Input Voltage, VIN ----------------------------------------------------------------------------------------------- 2.5V to 5.5V
Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range -------------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 3.6V, CIN = 10μF, COUT = 1μF, L = 10μH, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
2.5
--
5.5
V
Input Power Supply
Input Supply Voltage
VIN
VIN Quiescent Current
IQ
PWM, No Switching
--
0.6
--
mA
Shutdown Current
ISHDN
VIN = 4.2V, EN = GND
--
1
3
A
Under-Voltage Lockout
Threshold
VUVLO
VIN Falling, Check IQ < 200A
--
--
2.3
V
Under-Voltage Lockout
Hysteresis
VUVLO
After UVLO, VIN Rising,
Until IQ > 200µA
--
200
--
mV
Backlight LED Current Source
Accuracy of Output Current
ILED_ACC
FB1, FB2 = 0.15V, IFB1 = IFB2 = 20mA
5
--
5
%
Matching of Output Current
ILED_MAT
FB1, FB2 = 0.15V, IFB1 = IFB2 = 20mA
3
--
3
%
Operating Frequency
f SW
Reg0x03 [6] = 1
0.88
1.1
1.32
MHz
Maximum Duty Cycle
DMAX
FB1 = FB2 = 0V, check MAX duty
90
95
--
%
Brightness Ramp Rate
TRAMP
Reg0x03 [5:0] = 111111
Oscillator and Timing
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209.72 262.14 314.58
ms
is a registered trademark of Richtek Technology Corporation.
DS4501/A-00
September 2014
RT4501/A
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Power Switch
N-MOSFET On-Resistance
RDS(ON)_N VIN = 3.6V
90
175
350
m
N-MOSFET Current Limit
IOCP
0.8
1
1.2
A
N-MOSFET Leakage
Current
ILEAK
LX = 24V, No Switching
--
--
1
A
Reg0x02 [7] = 0
14
16
18
V
Reg0x02 [7] = 1
24.5
25.5
26.5
V
--
150
--
°C
Protection Function
Over Voltage Protection
Thermal Shutdown
Threshold
OVP
TSD
Thermal latch
Logic Control
Logic-High
VENH
1.3
--
--
Logic-Low
VENL
--
--
0.4
Logic-High
VPWML
1.3
--
--
Logic-Low
VPWML
--
--
0.4
Logic-High
VSCLH
1.3
--
--
Logic-Low
VSCLL
--
--
0.4
Logic-High
VSDAH
1.3
--
--
Logic-Low
VSDAL
--
--
0.4
EN Pull-Down Resistance
--
400
--
k
PWM Pull-Down Resistance
--
400
--
k
f SCL
--
--
400
kHz
tOFF
1
--
--
ms
tHigh_Min
0.2
--
--
s
tLow
0.2
--
500
s
EN Input
Voltage
PWM Input
Voltage
SCL Input
Voltage
SDA Input
Voltage
Clock Frequency of SCL
Pulse Dimming Control
EN Minimum Shut Down
Pulse Width
EN Minimum Logic High
Pulse Width
EN Minimum Logic Low
Pulse Width
V
V
V
V
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.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
DS4501/A-00
September 2014
is a registered trademark of Richtek Technology Corporation.
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5
RT4501/A
Typical Application Circuit
L
10µH
VIN
2.5V to 5.5V
RT4501/A
10
2
CIN
10µF
3
Enable
LX
VOUT 9
COUT
1µF
VIN
VOUT
EN
1
PWM
4 SCL
5
SDA
8, 11 (Exposed Pad)
GND
FB1 7
FB2 6
Timing Diagram
PWM Dimming
Reg0x04 = FF Reg0x04 = Reg0x02 = C7 Count 2^17
Clock
As Reg Default
00
PWM Enable
EN
Count 2^17
Clock
Reg0x02<0> = 0
DEV_EN Disable
Duty =50%
PWM
I(MAX)
I(MAX)/2
I(LED)
I(MIN)
0
0
Note : PWM prd : count by OSC : 17.6MegHz
> 1024 : Resolution = 7bits & < 1000 : Resolution = 8bits
Pulse Dimming
32µs/step x 127 steps
POR = 1 & EN power on
Hold at least 50µs
EN
32µs/step x 127 steps
Ton > 0.2µs
0.2µs < Toff < 500µs
1ms
7bits = 1111111 =
I(LED)max *[127/128+1/256]
MAX
7bits = 1111010
I(LED)
MIN
OFF
32µs/step
32µs/step
7bits = 0000000 =
I(LED)max*1/256
7bits = 1111111
7bits = 1111100
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is a registered trademark of Richtek Technology Corporation.
DS4501/A-00
September 2014
RT4501/A
Protection Timing
OTP
EN
2ms
sOTP
2ms
sEnbl
Reg0x05
record
Register
LED Short
EN
FB1 or FB2 Short
2ms
2ms
sEnbl
Reg0x05
record
Register
LED Open
EN
40 times
sOVP
… x 39 times
sEnbl
Register
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
DS4501/A-00
September 2014
Reg0x05
record
is a registered trademark of Richtek Technology Corporation.
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7
RT4501/A
Typical Operating Characteristics
Power On
Power Off
VEN
(2V/Div)
VEN
(2V/Div)
VOUT
(10V/Div)
VOUT
(10V/Div)
ILX
(200mA/Div)
ILX
(200mA/Div)
CIN = 10μF, COUT = 1μF, L = 10μH
CIN = 10μF, COUT = 1μF, L = 10μH
Time (5ms/Div)
Time (10ms/Div)
Efficiency vs. Output Current
Efficiency vs. Input Voltage
100
100
95
95
90
VIN = 3.7V
VIN = 4.2V
85
80
Efficiency (%)
Efficiency (%)
90
75
70
65
60
ILED = 20mA
ILED = 30mA
85
80
75
70
65
60
55
55
CIN = 10μF, COUT = 1μF, L = 10μH
50
CIN = 10μF, COUT = 1μF, L = 10μH
50
0
5
10
15
20
25
30
2.5
3
Output Current (mA)
4
4.5
5
5.5
Input Voltage (V)
OVP Threshold vs. Input Voltage
LED Current Accuracy vs. Input Voltage
26
2.00
1.80
Reg0x02 [7] = 1, 23V
24
1.60
ILED _30mA
ILED_20mA
1.40
OVP Threshold (V)
LED Current Accuracy (%)
3.5
1.20
1.00
0.80
0.60
0.40
22
20
18
Reg0x02 [7] = 0, 16V
16
0.20
6S2PWLED
0.00
2.5
3
3.5
4
4.5
5
Input Voltage (V)
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8
5.5
14
2.5
3
3.5
4
4.5
5
5.5
Input Voltage (V)
is a registered trademark of Richtek Technology Corporation.
DS4501/A-00
September 2014
RT4501/A
PWM Dimming Operation
PWM Dimming
35
LED Current (mA)
30
ILED2 = 20mA
ILED1 = 20mA
25
20
VPWM
(2V/Div)
15
ILED2 = 20mA
ILED1 = 20mA
10
I LED
(10mA/Div)
5
Frequency = 20kHz, Duty Cycle = 50%
0
0
10
20
30
40
50
60
70
80
90
100
Time (10μs/Div)
Dimming Duty (%)
Quiescent Current vs. Input Voltage
800
1.11
700
Quiescent Current (μA) 1
Switching Frequency (MHz)1
Switching Frequency vs. Input Voltage
1.12
1.10
1.09
1.08
1.07
1.06
Non-Switching
600
500
400
300
200
100
CIN = 10μF, COUT = 1μF, L = 10μH
1.05
2.5
3
3.5
4
4.5
5
0
5.5
2.5
3
Input Voltage (V)
3.5
4
4.5
5
5.5
Input Voltage (V)
Shutdown Current vs. Input Voltage
Enable Voltage vs. Input Voltage
0.35
0.94
Enable Voltage (V)
Shutdown Current (μA)1
0.30
0.25
0.20
0.15
0.10
0.93
Enable
Shutdown
0.92
0.05
0.00
0.91
2.5
3
3.5
4
4.5
5
Input Voltage (V)
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
DS4501/A-00
September 2014
5.5
2.5
3
3.5
4
4.5
5
5.5
Input Voltage (V)
is a registered trademark of Richtek Technology Corporation.
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RT4501/A
Table 1. Pulse Dimming Register Map
Slave address =0100010x
Address
Address
Name
0x00
Device ID
0x01
0x02
0x03
0x05
Manufacture
Config1
Timing
FLAG
BIT
LABEL
Description
7:0
DEV_ID
7:2
REV
000000
Revision number
1:0
VID
11
Vendor ID : Richtek
7
OVPsel
1
OVP threshold ([0] 16V, [1] 25.5V)
6
Reserved
5
Reserved
4
Reserved
3
MAX_Current 0
[0] 20mA, [1] 30mA,
2
LED1_EN
1
Backlight LED1 : [0] OFF, [1] ON
1
LED2_EN
1
Backlight LED2 : [0] OFF, [1] ON
0
DEV_EN
1
CHIP enable : [0] OFF, [1] ON
7
RST_SW
0
Software reset : [0] Disable(Auto), [1] Reset
all registers
6
FSW
1
Switching frequency ([0]550kHz, [1]1.1MHz)
5:0
Reserved
7:4
Reserved
0
3
LED1_FT
0
LED1 short : [0] Normal, [1] Fault
2
LED2_FT
0
LED2 short : [0] Normal, [1] Fault
1
OVP
0
Output over voltage : [0] Normal, [1] Fault
0
OTP
0
Over temperature : [0] Normal, [1] Fault
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
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Default
(Reset Value)
is a registered trademark of Richtek Technology Corporation.
DS4501/A-00
September 2014
RT4501/A
Table 2. PWM Dimming Register Map
Slave address =0100010x
Address
Address
Name
0x00
Device ID
0x01
0x02
Manufacture
Config1
BIT
0x04
0x05
7:2
REV
000000
Revision number
1:0
VID
11
Vendor ID : Richtek
7
OVPsel
1
OVP threshold ([0] 16V, [1] 25.5V)
6
PWM_EN
0
PWM enable : [0] Ignored, [1] Enable
0
PWM active setup : [0] High active, [1] Low
active
5
PWM _SET
4
Reserved
3
MAX_Current 0
[0] 20mA, [1] 30mA,
2
LED1_EN
1
Backlight LED1 : [0] OFF, [1] ON
1
LED2_EN
1
Backlight LED2 : [0] OFF, [1] ON
0
DEV_EN
1
CHIP enable : [0] OFF, [1] ON
7
RST_SW
0
Software reset : [0] Disable(Auto), [1] Reset
all registers
6
FSW
1
Switching frequency ([0]550kHz, [1]1.1MHz)
000
Brightness ramp-up rate : [000] 32s, [001]
4.096ms,
[010] 8.192ms, [011] 16.383ms, [100]
32.768ms,
[101] 65.536ms, [110] 131.072ms, [111]
262.144ms
UP_RATE
Timing
Linear
Brightness
Control
FLAG
Description
DEV_ID
2:0
DN_RATE
000
Brightness ramp-down rate : [000] 32µs, [001]
4.096ms,
[010] 8.192ms, [011] 16.383ms, [100]
32.768ms,
[101] 65.536ms, [110] 131.072ms, [111]
262.144ms
7:0
BRIGHT_LIN
11111111
[00000000] 0.39%, [00000001] 0.39%,
……
[111111111] 100%
7:4
Reserved
0
3
LED1_FT
0
LED1 short : [0] Normal, [1] Fault
2
LED2_FT
0
LED2 short : [0] Normal, [1] Fault
1
OVP
0
Output over voltage : [0] Normal, [1] Fault
0
OTP
0
Over temperature : [0] Normal, [1] Fault
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
DS4501/A-00
Default
(Reset Value)
7:0
5:3
0x03
LABEL
September 2014
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RT4501/A
Application Information
LED Short Protection
LED short protection prevents abnormal connection to
cause IC damage avoiding FB1/FB2 connecting power
supply. And, If unbalanced LEDs series (cause FB1 or
FB2 >12V) is different between channel1 and channel2,
IC will also occur LED short event. As LED short event
occur more than deglitch time 2ms, IC will shut-down latch
until IC is reset by EN pin.
Soft-Start
The RT4501/A includes a soft-start function to avoid high
inrush current during start-up. The soft-start function is
achieved by clamping the output voltage of the error
amplifier with another voltage source that is increased
slowly from zero to near VIN during the soft-start period.
threshold, the device is shut down. If the input voltage
rises over under-voltage lockout hysteresis (200mV
typical), the IC restarts.
Linear Brightness Dimming
The chip is built-in an I2C 8-bit resolution brightness control
with maximum 20mA/30mA selection. Reg0x02 <3>
corresponds to full-scale LED current control. Reg0x04
<7:0> sets 8bits resolution brightness dimming control.
ILED =
Code
 ILED, Full
255
Where
ILED, Full : the full-scale LED current set by Reg0x02 <3>.
Code : the 8bit brightness code Reg0x04 <7:0>
programmed by I2C interface.
OCP Protection
The RT4501/A features a 1A current limitation. The current
flowing through the inductor during a charging period is
detected by a current sensing circuit. If the value exceeds
the current limit, the N-MOSFET will be turned off. The
inductor will then be forced to leave charging stage and
enter discharging stage. Therefore, the inductor current
will not increase to reach current limit.
The over-temperature protection function will be latched
at shutdown status when the junction temperature
exceeds 165°C for 2ms. After re-power on sequence, the
converter will automatically resume switching.
OVP Protection
The chip provides over-voltage protection function to limit
the output voltage in abnormal conditions. The OVP
threshold voltage is 25.5V/16V by selecting Reg0x02 <7>.
Once the LED is open, the output voltage will be limited
at OVP protection level to avoid device breakdown.
PWM Brightness Dimming
Besides programmable built-in I2C backlight LED current
control, the RT4501/A features a built-in PWM dimming
current control by setting Reg0x02 <6> to 1, offering a
linear current dimming by external clock source. In order
to guarantee the PWM dimming resolution (7 bit at >
15kHz application), recommending dimming frequency
have to be operated at range of 400Hz to 20kHz.
Pulse Brightness Dimming
The EN pin features a simple digital interface to allow
digital brightness control. Using the one-wire dimming
brightness control can achieve as high as 128 steps
resolution, recommending dimming pulse is larger than
0.2μs. RT4501/A keeps shunt down status, when EN pin
is pulled low keeping 1ms.
1 
 Code
ILED = 
+
  ILED, Full
256 
 128
Where
Under-Voltage Lockout
ILED, Full : the full-scale LED current set by Reg0x02 <3>.
An under-voltage lockout circuit prevents the operation of
the device at input voltages below under-voltage threshold
(2.3V maximum). When the input voltage is below the
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12
is a registered trademark of Richtek Technology Corporation.
DS4501/A-00
September 2014
RT4501/A
The recommended inductor value for dual-channel 6
WLEDs applications is 10μH. When selecting the
inductor, the inductor rated saturation current should be
higher than the peak current at maximum load. Small size
and better efficiency are major concerns for portable
devices. The inductor should have low core loss at 1.1MHz
and low DCR for better efficiency.
Capacitor Selection
10μF input ceramic capacitor and 1μF output ceramic
capacitor are recommended for driving dual-channel 6
WLEDs applications. For better voltage filtering, ceramic
capacitors with low ESR are recommended. X5R and X7R
types are suitable because of their wide voltage and
temperature ranges.
Thermal Considerations
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.
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
WL-CSP-10B 0.87x2.07 (BSC) package, the thermal
resistance, θJA, is 99.6°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 :
resistance, θJA. The derating curve in Figure 1 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
1.2
Maximum Power Dissipation (W)1
Inductor Selection
Four-Layer PCB
1.0
0.8
0.6
0.4
0.2
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 1. Derating Curve of Maximum Power Dissipation
Layout Consideration
As for all switching power supplies, the layout is an
important step in the design, especially at high peak
currents and switching frequencies. If the layout is not
carefully done, the regulator might expose noise problems
and duty cycle jitter. Therefore, use wide and short traces
for high current paths. The input capacitor should be placed
as close as possible to the input pin for good input voltage
filtering. The inductor should be placed as close as possible
to the switch pin to minimize the noise coupling into other
circuits. The output capacitor needs to be placed directly
from the VOUT pin to GND rather than across the LEDs.
This reduces the ripple current in the trace to the LEDs.
When doing the PCB layout, the bold traces should be
routed first, as well as placement of the inductor, and input
and output capacitors.
P D(MAX) = (125°C − 25°C) / (99.6°C/W) = 1W for
WL-CSP-10B 0.87x2.07 (BSC) package
The maximum power dissipation depends on the operating
ambient temperature for fixed T J(MAX) and thermal
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
DS4501/A-00
September 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
13
RT4501/A
Outline Dimension
Symbol
Dimensions In Millimeters
Dimensions In Inches
Min.
Max.
Min.
Max.
A
0.500
0.600
0.020
0.024
A1
0.170
0.230
0.007
0.009
b
0.240
0.300
0.009
0.012
D
2.020
2.120
0.080
0.083
D1
E
1.600
0.820
0.063
0.920
0.032
0.036
E1
0.400
0.016
e
0.400
0.016
10B WL-CSP 0.87x2.07 Package (BSC)
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.
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DS4501/A-00
September 2014