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PDF SC618 Data sheet ( Hoja de datos )
| Número de pieza | SC618 | |
| Descripción | Charge Pump Flash LED Driver | |
| Fabricantes | Semtech | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de SC618 (archivo pdf) en la parte inferior de esta página. Total 13 Páginas | ||
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SC618
Charge Pump Flash LED
Driver with Safety Timer
POWER MANAGEMENT
Features
Flash and spotlight — two selectable modes
Flash mode — up to 700mA output
Flash mode — 500mA max output (over rated voltage,
temperature, and load conditions)
Flash mode safety timer shut-off — 1 second
Spotlight mode set to 40% of flash current
Spotlight mode — up to 280mA output
Spotlight mode —1x mode (under most conditions)
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Input range — 3.0V to 5.25V
External flash control pin for synchronization to a cam-
era module or graphics controller
Short-circuit, over-voltage, and over-temperature pro-
tection
Soft-start functionality
Separate flash and spotlight control inputs for maxi-
mum versatility
Ultra-thin package MLPD-UT-10 — 3mm x 3mm x
0.6mm
Applications
Mobile camera phones
Digital cameras
PDAs with built-in cameras
Description
The SC618 is a high-current charge pump designed spe-
cifically for use with white LEDs used in camera flash
applications. Only two small bucket capacitors are required
to develop the output drive, providing a low EMI solution
compared to inductive boost regulators.
The SC618 has two modes of operation: flash mode and
spotlight mode. In flash mode, the SC618 is capable of
delivering 500mA of regulated current for a duration of
500ms or up to 700mA for a reduced duration. A safety
timer is also included to ensure the LED cannot be left on
indefinitely and overheat. In spotlight mode the SC618
outputs 40% of the flash mode current and can remain
enabled continuously.
An external resistor is connected in series with the LED to
set the current. In flash mode, this resistor can dissipate
up to 175mW, reducing the power dissipation require-
ment of the SC618. The flash input overrides the control
input to make sure the flash function is activated .
The SC618 ultra-thin package provides both a low profile
and high thermal efficiency.
Typical Application Circuit
VBAT
10μF
1μF
August 2, 2007
1μF
FLASH
CTRL
SC618
VIN VOUT
C1+ GND
C1- ISET
C2+ CTRL
C2- FLASH
1μF
White LED
RSET
1
1 page  
SC618
Typical Characteristics
Flash Current at 10ms, R = 500mΩ, V = 3.75V
ISET OUT
515
510
505
500
495
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485
3.3 3.45 3.6 3.75 3.9 4.05 4.2
VIN (V)
Flash Current at 500ms, R = 500mΩ, V = 3.58V
ISET OUT
515
510
505
500
495
490
485
3.3 3.45 3.6 3.75 3.9 4.05 4.2
VIN (V)
Flash Duration, RISET = 350mΩ, VOUT = 3.86V
(start), 3.61V (LED Heated 500ms)
755
735
715
695
675
0
VIN=4.2V
VIN=3.7V
100 200 300
Pulse Duration (ms)
VIN=3.4V
VIN=3.3V
400 500
Flash Current at 100ms, R = 500mΩ, V = 3.68V
ISET OUT
515
510
505
500
495
490
485
3.3
3.45
3.6 3.75 3.9
VIN (V)
4.05
4.2
Spotlight Current, RISET = 500mΩ, VOUT = 3.16V
220
212
Transition to
2x Mode
204
1x Mode
196
188
180
5.25 4.8 4.35 3.9 3.45
VIN (V)
3
Flash Duration, R = 500mΩ, V = 3.75V (start),
ISET OUT
3.58V (LED Heated 500ms)
515
509
VIN=3.7V
503
497
VIN=4.2V
VIN=3.3V
491
485
0
100 200 300
Pulse Duration (ms)
400
500
5
5 Page 
SC618
Applications Information (continued)
PCB Layout Considerations
The following layout is suggested for a two-layer design.
The capacitors C1 and C2 are the bucket capacitors and
each conducts the full load current of up to 500mA pulsed
for one half clock cycle. C3 is the output decoupling
capacitor placed near the VOUT pin. C4 is the input
decoupling capacitor placed near the VIN pin. Multiple
vias should be used whenever it is necessary to change
layers on nets connecting to pins VIN, VOUT, GND, C1-,
C1+, C2- and C2+.
while in flash or spotlight mode. It is critical to maintain
adequate ground plane around the device to maximize
heat transfer and avoid over-temperature shutdown.
wwTwh.eDalotaaSdhecuetr4rUe.nctomreturn path is from the ISET sense point
through the resistor and back to the ground pins.
Resistance in this path adds to the total resistance and
has the effect of reducing the LED current by about 4%
per 10mV of DC drop across the return copper trace in
flash mode. For this reason, it is crucial to have a low resis-
tance return path. Place and ground the resistor as close
as possible to the ground pin of the SC618. The trace from
the ISET pin has virtually no current. The ISET trace should
make contact at the pad of the power sense resistor to
minimize the effect of voltage drop between the LED
cathode and the resistor.
Resistor R1 is routed with a very low resistance connec-
tion between R1 and GND pin 3. The sense trace between
Pin 6 and R1 is routed around the ground vias, allowing
the shortest ground return path possible. The sense trace
is connected to R1 at the positive terminal pad for the
most accurate output possible. The bottom copper layer
is mostly a ground plane with no obstructions between
the ground vias. The smaller rectangle to the left con-
nects the input power to VIN pin 1 and input capacitor
C4. The two traces at the lower left are for logic inputs
FLASH and CTRL. The trace to the right is the ISET pin
sense trace. The sense trace is routed out of the path of
the returning ground current.
Thermal Resistance Considerations
The SC618 package is thermally efficient when the circuit
board layout connects the thermal pad through multiple
vias to the ground plane. The thermal resistance is rated
at 49°C/W, and this rating is dependent on the connec-
tion between the thermal pad and the ground plane. The
layout should keep the junction temperature below the
OTP limit while operating the SC618 within the specified
electrical conditions for I and V . A poor layout may
OUT ISET
allow the junction temperature to reach the OTP limit
11
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet SC618.PDF ] | |
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