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PDF SC4505 Data sheet ( Hoja de datos )

Número de pieza SC4505
Descripción High Efficiency Boost Converter
Fabricantes Semtech Corporation 
Logotipo Semtech Corporation Logotipo



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No Preview Available ! SC4505 Hoja de datos, Descripción, Manual

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.
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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.
SC4505
High Efficiency Boost Converter
for Backlight/Flash LED Driver
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
21
10BQ015
D2
LED
C1
D3
LED
2.2uF
0 16
FL_TRB
EN_FL
EN_BL
AGND
C3 15
0.33uF
14
13
12
11
RO1SET
6.98k
10
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
LED
D5
LED
D6 D7
LED LED
C4
12n
(Optional)
C5
12n
(Optional)
0
Power
Ground
0
Analog
Ground
0
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
Input Voltage (V)
5
All Capacitors are Ceramic.
Figure 1. SC4505 Application Circuit for Backlight and Flashlight LED Driver
Revision: December 15, 2006
1
www.semtech.com

1 page




SC4505 pdf
SC4505
POWER MANAGEMENT
PBilnocDkeDsciarigprtaiomns
Pin
Pin Name
Pin Function
1,2
3,4
5
6
7
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9
10
PGND
SW
VO
IO2
IO1
COMP
AGND
IO2SET
11 IO1SET
12 EN_BL
13 EN_FL
14 FL_TRB
15 FTO
16 VIN
Exposed Pad
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.
EN_FL
0
0
1
1
FL_TRB
Status
0 Flash disable
1 Flash disable
0 20% max. output current set by
external resistor, RO2SET
1 100% max. output current set
by external resistor, RO2SET
Table 1
Note: When EN_FL = 0
FL_TRB = 0
EN_BL = 0
The boost is turned OFF and disabled.
EN_BL
0
1
Status
Backlight disable
Backlight enable
Table 2
2006 Semtech Corp.
5
www.semtech.com

5 Page





SC4505 arduino
POWER MANAGEMENT
Applications Information
VIN
L1
D1
VOUT
COUT
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SC4505
COMP
R1
R2
VOVP
I1
R3
VO
R4
I2
Figure 5. OVP Tweaking
As shown in Figure 5, R1 and R2 are the internal resistor
divider. R3 and R4 are external resistor divider for OVP
triggering point adjustment. It is noted that the resistance
of the internal resistor divider formed by R1 and R2 is
around 500kΩ. When OVP happens, a strong pulldown
will be applied to VO pin to quickly discharge the output
capacitor. Any large
discharge process at
OvVaPl uceonodfitRio3n.wGi lel nselroawllydsopweankitnhge,
small value of R3 is preferred in applications.
However, small value of the resistor divider formed by
R3 and R4 would cause additional power loss. People
often use R4=100kand then select R3 according to
the OVP specification. In this case, the OVP triggering
threshold estimation equation can be rewritten as
follows:
VOVP
=
R4//500KΩ + R3
R 4 //500K
× 28V
Set
R4 = 100K
We can get
R3
=

VOVP
28V
1 × 83.3K
iTnhedetotelermrainncinegotfhteheORV3PatnridggRe4rsinhgouplodinatls. oUsbueaclloyntshideerereids
about 5%~8% difference between the calculated value
and the measure OVP triggering threshold.
2006 Semtech Corp.
11
SC4505
www.semtech.com

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