SC4505 Datasheet, PDF (1/15 Pages) Semtech Corporation – High Efficiency Boost Converter for Backlight/Flash LED Driver

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
Typical Application Circuit
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
VIN: 2.6V ~ 6.0V
PGND
C2
2.2u
L1
IHLP-2525CZ-01-1R5-M-01
LED: SML-LX0603UWD
D1
2
1
10BQ015
D2
D3
LED
LED
C1
2.2uF
0
16
FL_TRB
EN_FL
EN_BL
AGND
C3
15
0.33uF
14
13
12
11
RO1SET
10
6.98k
9
RO2SET
1.54k
VIN
FTO
FL_TRB
EN_FL
EN_BL
IO1SET
IO2SET
AGND
SC4505
PGND ¹
PGND ²
SW ³
SW ⁴
VO ⁵
IO2 ⁶
IO1 ⁷
COMP ⁸
0
R1
1.47k C6
12n
0 ^D4
D5
LED
LED
D6
D7
LED LED
C4
12n
(Optional)
C5
12n
(Optional)
0
0
0
Power
Ground
Analog
Ground
Boost Converter Efficiency vs Input Voltage
(2 String of 3 LEDs @30mA)
87
85
83
81
79
77
2.5
3
3.5
4
4.5
5
Input Voltage (V)
All Capacitors are Ceramic.
Figure 1. SC4505 Application Circuit for Backlight and Flashlight LED Driver
Revision: December 15, 2006
1
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