SC4505
High Efficiency Boost Converter
for Backlight/Flash LED Driver
POWER MANAGEMENT
Description
The SC4505 is a high-frequency PWM current-mode step-
up switching regulator with an integrated 2A power tran-
sistor. Its high switching frequency (1MHz) allows the use
of tiny surface-mount external passive components. The
internal switch is rated at 36V which makes the con-
verter ideal for multiple LED series operation with opti-
mal current matching. Two programmable independent
current source structure allows dual panel LED backlight
and flash operation.
The operating frequency of the SC4505 is set at 1MHz.
The selected operating frequency gives the SC4505 de-
sign flexibility for size, cost and efficiency optimization.
The SC4505 is available in thermally enhanced 16-pin
MLPQ package (3x3x0.9mm) with embedded over tem-
perature protection.
Features
Two independent current sources for dual LED strands
with optimal current/light matching. Backlight up to
75mA, Flash up to 125mA
Wide input range from 2.6V to 12V
Adaptive output voltage up to 28V with OVP protec-
tion against open circuit conditions
Low shutdown current (<1µA )
Internal Flash/Torch mode with flash timeout to pro-
tect LEDs
1MHz Fixed Frequency Current-Mode Control
Internal 2A current limit for driving large numbers of
LEDs
Supports PWM Dimming from 50Hz to 50kHz
Internal undervoltage lockout
Small, low profile, thermally enhanced 16-MLPQ pack-
age is fully WEEE and RoHS compliant
Applications
White LED power supplies
Flat screen LCD bias supplies
TFT bias supplies
Dual panel Handset/Liquid Crystal Display Monitor
Portable media players
Digital video cameras
Digital still cameras
Boost Converter Efficiency vs Input Voltage
(2 String of 3 LEDs @30mA)
87
Typical Application Circuit
L1
IHLP -2525CZ-01-1R5-M-01
C2
PGND
2.2u
C1
VIN: 2.6 V ~ 6.0V
LED: SML-LX0603UWD
2
D1
1
D2
L ED
D3
L ED
10BQ015
2.2u F
0
C3
0 .33uF
SC4505
16
15
14
13
12
11
VIN
FTO
FL_TRB
EN_FL
EN_BL
IO1SET
IO2SET
AGND
PGND
PGND
SW
SW
VO
IO2
IO1
COMP
1
2
3
4
5
6
7
8
R1
3.0 1k
C6
12n
85
D5
L ED
0
0
Efficiency (%)
C5
12n
(Optional)
D4
L ED
FL_TRB
EN_FL
EN_BL
AGND
RO1SET
6.9 8k
83
D6
L ED
D7
L ED
81
10
9
RO2SET
1.5 4k
C4
12n
(Optional)
79
0
0
0
77
2.5
3
3.5
4
4.5
5
Input Voltage (V)
Power
Ground
Analog
Ground
All Capacitors are Ceramic.
Figure 1. SC4505 Application Circuit for Backlight and Flashlight LED Driver
Revision: December 12, 2007
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SC4505
POWER MANAGEMENT
Absolute Maximum Rating
Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified
in the Electrical Characteristics section is not implied. Exposure to Absolute Maximum rated conditions for extended periods of time may affect device
reliability.
Parameter
Supply Voltage
SW Voltage, Output Voltage, Current Source Voltage
I
0SET
Voltage
FTO Voltage
EN_BL, EN_FL, FL_TRB Voltage
Thermal Resistance Junction to Ambient
Maximum Junction Temperature
Storage Temperature Range
IR Reflow (Soldering) 10s to 30s
ESD Rating (Human Body Model)
Symbol
V
IN
V
SW
, V
O
, V
IO1
, V
IO2
V
IO1SET,
V
IO2SET
V
FTO
V
EN_BL
, V
EN_FL
V
FL_TRB
θ
J A
T
J
T
STG
T
PKG
ESD
Typ
-0.3 to 20
-0.3 to 36
-0.3 to 2
-0.3 to V
IN
+ 0.3
-0.3 to V
IN
+ 0.3
37
150
-65 to +150
260
1
Units
V
V
V
V
V
°C/W
°C
°C
°C
kV
Unless specified: V
IN
= 3.6V, -40°C < T
A
= T
J
< 85°C, R
O1SET
=6.98K
Ω
,
R
O2SET
=1.54K
Ω
Electrical Characteristics
Parameter
Supply Input Voltage V
IN
UVLO Threshold
UVLO Hysteresis
V
IN
Supply Current
V
IN
Supply Current in Shutdown
Switching Frequency
Maximum Duty Cycle
Minimum Duty Cycle
Switch Current Limit
Switch Leakage Current
Switch Saturation Voltage
EN_FL, FL_TRB, EN_BL
High Voltage
EN_FL, FL_TRB, EN_BL
Low Voltage
Test Conditions
Min
2.6
Typ
Max
12
Unit
V
V
mV
mA
V
IN
rising
2.45
50
2.59
Not switching
EN_FL = FL_TRB = EN_BL = 0
T
J
= 25°C
0.8
85
1.7
1.0
1
90
0
1.75
2.25
0.01
300
2
0.4
1
1.2
µA
MHz
%
%
A
µA
mV
V
V
V
S W
= 28V
I
SW
= 1A
V
IN
= 2.6V to 4.7V
V
IN
= 2.6V to 4.7V
2
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SC4505
POWER MANAGEMENT
Electrical Characteristics (Cont.)
Parameter
EN_FL, FL_TRB, EN_BL
Input Current
EN_BL PWM Dimming
Control Frequency
EN_BL PWM Dimming
Control Duty Cycle
FTO Sourcing Current
FTO Trip Threshold Voltage
FTO Pull Down Current
Overvoltage Protection
Thermal Shutdown Temperature
Thermal Shutdown Hysteresis
Backlight Current Accuracy ( I
O1
)
Max Backlight Current ( I
O1
)
Flash Current Accuracy ( I
O2
)
Max Flash Current ( I
O2
)
Torch Output Current ( I
O2
)
I
O1
Off Leakage Current
I
O2
Off Leakage Current
V
O
Pulldown in Overvoltage Fault
Note 1: Guaranteed by Design
Unless specified: V
IN
= 3.6V, -40°C < T
A
= T
J
< 85°C, R
O1SET
=6.98K
Ω
,
R
O2SET
=1.54K
Ω
Test Conditions
V
EN_FL
= 0V to 4.7V
Note 1
F
PWM
=32kHz , Note 1
EN_FL = FL_TRB = 1
Min
Typ
0.01
Max
1
50K
100
Unit
µA
Hz
%
µA
V
mA
V
°C
°C
50
12
1.2
1.25
EN_FL = 1, FL_TRB = 0
2.6
28
155
10
EN_BL = 1
T
J
= 25°C, R
O1SET
=6.98K
Ω
19
20
75
21
mA
mA
EN_FL = FL_TRB = 1
T
J
= 25°C, R
O2SET
=1.54K
Ω
92
100
125
108
mA
mA
mA
EN_FL=1, FL_TRB=0
T
J
= 25°C, R
O2SET
=1.54K
Ω
V
IO1
=28V
V
IO2
=28V
18
0.1
0.1
7
1
1
µA
µA
KΩ
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SC4505
POWER MANAGEMENT
Pin Configurations
TOP VIEW
Ordering Information
Device
(1)(2)
SC4505MLTRT
SC4505EVB
(3)
P ackag e
MLPQ-16
Temp. Range( T
A
)
-40 to 85°C
EVALUATION BOARD
Notes:
(1) Only available in tape and reel packaging. A reel
contains 3000 devices.
(2) Lead free product. This product is fully WEEE and
RoHS compliant.
(3) Consult factory for all other available options.
(16 Pin - MLPQ)
Block Diagram
VCC
VO
OVP
VOUT
UVLO
Thermal
Shutdown
S
R
OSC
Q
Sense
Amp
Comparator
Rsense-
5mOhm
Reference&
Internal Regulator
COMP
Error signal selection
and summation
ADJ1
ADJ1
EN_BL
BL Setpoint
IO1
EN_FL
FL Setpoint
FL_TRB
ADJ2
ADJ2
IO2
IO1SET
RO1SET
PGND
AGND
IO2SET
RO2SET
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SC4505
POWER MANAGEMENT
Pin Descriptions
Block Diagram
Pin
1,2
3,4
5
6
7
8
9
10
11
12
13
14
15
16
Pin Name
PGND
SW
VO
IO2
IO1
COMP
AGND
IO2SET
IO1SET
EN_BL
EN_FL
FL_TRB
FTO
VIN
Exposed Pad
Pin Function
Power ground.
Collector of the internal power transistor. Connect to the boost inductor and the rectifying diode.
Boost output voltage pin. Internal overvoltage protection also monitors the voltage at this pin.
Connect the output capacitor and the anode of the LED strings to this pin.
Provides constant source current to LED string 2.
Provides constant source current to LED string 1.
The output of the internal transconductance error amplifier. This pin is used for loop
compensation.
Analog ground.
Current source IO2 value set pin. By selecting the resistor connected from this pin to GND, the
corresponding maximum current on string 2 is set.
Current source IO1 value set pin. By selecting the resistor connected from this pin to GND, the
corresponding maximum current on string 1 is set.
Enable and Brightness control pin for LED backlight string 1. (See Table 2 for logic).
Enable and Brightness control pin for LED flash light string 2. (See Table 1 for logic).
Flash time out pin. By selecting the capacitor connected to this pin, the time out duration is
determined. By pulling this pin to AGND, the FTO function is disabled.
Power Supply Pin. Bypassed with capacitors close to the pin.
The exposed pad must be soldered to the analog ground plane on the PCB for good thermal
conduction.
E N _F L
0
0
1
1
F L _T R B
0
1
0
1
Status
Flash disable
Flash disable
20% max. output current set by
external resistor, RO2SET
100% max. output current set
by external resistor, RO2SET
E N _B L
0
1
Status
Backlight disable
Backlight enable
Table 2
Table 1
Note: When
EN_FL = 0
FL_TRB = 0
EN_BL = 0
The boost is turned OFF and disabled.
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