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PDF SC4539 Data sheet ( Hoja de datos )
| Número de pieza | SC4539 | |
| Descripción | High Effi ciency Boost Converter | |
| Fabricantes | Semtech Corporation | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de SC4539 (archivo pdf) en la parte inferior de esta página. Total 14 Páginas | ||
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POWER MANAGEMENT
SC4539
High Efficiency Boost Converter
for up to 6 LEDS
Features
Input voltage range — 2.8V to 5.5V
Current-mode PWM control — 800kHz
Programmable LED current up to 30mA
Soft-start to reduce in-rush current
PWM dimming — 100Hz to 50kHz
PWM dimming at ISET — Analog and filtered
www.DataSheeOt4vUe.cr-ovmoltage protection — 25V (max.)
Under-voltage lockout (UVLO)
Thermal shutdown
Shutdown current — <1μA
Ultra-thin package — 2mm x 2mm x 0.6mm
Lead-free package, WEEE and RoHS compliant
Applications
White LED Display Backlight Driver
Smartphones and PDAs
Cellular Handsets
MP3 and Portable Media Players
DSC, GPS, Satellite Radio, Game Players
Typical Application Circuit
Description
The SC4539 is designed to regulate current for a series
chain of white LEDs in LCD backlighting applications
where small size and high efficiency are priorities. This
device integrates an 800kHz current-mode PWM boost
converter and a 30mA programmable low dropout current
sink regulator.
An external resistor sets the LED current up to 30mA.
PWM dimming (100Hz to 50kHz) may be applied directly
to the enable (EN) pin, or dimming can be controlled by
applying an analog signal to the ISET circuit. The boost
circuit can output up to 22V (guaranteed) to drive up to 6
LEDs in series. The current regulator protects against
shorts between the BL and OUT pins and also eliminates
backlight glow during shutdown when using LEDs with
high leakage. Under-voltage lockout and thermal shut-
down provide additional protection. A small external
capacitor and series resistor control soft-start and loop
compensation. Over-voltage detection protects the
SC4539 if the LED pin is floating or shorted to ground.
The SC4539 is available in an MLPD-8 pin 2mm x 2mm x
0.6mm package, with a rated temperature range of -40°C
to +85°C.
2.8 to
5.5V
CIN
L1
IN
D
LX
OUT
SC4539
COUT
Enable and
PWM dimming
RISET
CCOMP RCOMP
EN
ISET
COMP
GND
BL
September 5, 2007
1
1 page  
SC4539
Typical Characteristics
All data taken with V = 20V (6 white LEDs), R = 5.76kΩ (I = 20mA), V = 3.6V, L = 22μH, and efficiency (η) = P /P unless otherwise noted.
OUT ISET BL IN
LED IN
Efficiency vs. I
BL
100
3.6VIN
Efficiency vs. Output Voltage
90
80 86 5.5VIN
60
www.DataSheet4U.com 5.5VIN
40
2.8VIN
82
78
3.3VIN
2.8VIN
20 74
0
0 6 12 18 24 30
I (mA)
BL
Efficiency vs. Input Voltage
90
86
70
0
5 10 15 20 25
VOUT (V)
Efficiency vs. Input Voltage
90
6 LED
86
82
VOUT
78
LED
82
4 LED
78
74
70
2.8
90
86
82
78
74
70
2.8
3.3 3.9 4.4 5.0
VIN (V)
Efficiency vs. Input Voltage
20mA
10mA
30mA
3.3 3.9 4.4 5.0
V (V)
IN
5.5
5.5
74
70
2.8
6.0
4.0
2.0
0.0
-2.0
-4.0
-6.0
0
3.3 3.9 4.4 5.0 5.5
VIN (V)
Normalized I vs. Output Voltage
BL
5 10 15 20 25
V (V)
OUT
5
5 Page 
SC4539
Applications Information (continued)
Soft-Start
The soft-start mode reduces in-rush current by utilizing
the external compensation network. As the error amplifier
slowly charges the COMP node voltage, the duty cycle of
the boost switch ramps from 0% to its final value once in
regulation. The gradual increase of the duty cycle slowly
charges the output capacitor and limits in-rush current
during start up. Soft-start is implemented only when the
input power is cycled.
www.DataSheet4U.com
Thermal Shutdown
A thermal shutdown system is included for protection in
the event the junction temperature exceeds 155°C. In
thermal shutdown, the on-chip power switch is disabled.
Switching and sinking resumes when the temperature
drops by 20°C.
Current Limit
The power switch of the boost is protected by an internal
current limit function. The switch is opened when the
current exceeds the maximum current switch value.
Inductor Selection
The inductor value should be within the range of 4.7μH to
22μH. The DCR needs to be considered when picking the
inductor to ensure optimum efficiency. The largest induc-
tor package that can be tolerated in the circuit area should
be used since the DCR generally decreases with increasing
package size.
The saturation current of the inductor should be much
higher than the peak current of the internal boost switch
to ensure that the inductor never enters saturation during
normal operation of the part. The equation to calculate
the peak inductor current is
IL(Peak)
IIN ǻIL
2
where
ǻIL
VIN u D
L u fosc
D 1 VIN
VOUT
IIN
VOUT u IOUT
Ș u VIN
D is the duty cycle for continuous operation. Efficiency (η)
can be approximated by using the curves provided in the
Typical Characteristics section. Table 1 lists inductors that
have been proven to work with SC4539.
Table 1 -- Recommended Inductors
Part Number
Value DCR
Rated
Toler-
(μH) (Ω) Current (A) ance
Dimensions
(L x W x H)
(mm)
Coilcraft
LPS4018-223ML
22 0.360
0.70
±20% 3.9 x 3.9 x 1.7
Murata
LQH43CN150K03
Murata
LQH32CN150K53
15 0.320 0.570
15 0.580 0.300
±10% 4.5 x 3.2 x 2.6
±10% 3.2 x 2.5 x 1.55
Capacitor Selection
The input capacitor should be at least 2.2μF. A larger
capacitor will reduce the voltage ripple on the input. The
output capacitor values can range from 0.22μF to 1μF. The
compensation capacitor value should be 47nF. Capacitors
of X5R type material or better can be used for any of the
capacitors. See Table 2 for capacitors that can be used.
Table 2 -- Recommended Capacitors
Part Number
Input Capacitor
Murata
GRM188C70J225KE20
Output Capacitor
Murata
GRM21BR71H105KA12L
Compensation Capacitor
Taiyo Yuden
EMK105BJ473KV-F
Value
(μF)
Rated
Voltage (V)
Type Case Size
2.2 6.3 X7S 0603
1.0 50 X7R 0805
0.047 16 X7R 0402
11
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet SC4539.PDF ] | |
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