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POWER MANAGEMENT
SC615A
Charge Pump
Flash LED Driver
September 22, 2005
Typical Application Circuit
Applications
Features
Two Selectable Modes - Flash and Spotlight
Up to 700mA Output - Flash Mode
Up to 280mA Output - Spotlight Mode
500mA Over Temperature Range and Voltage
Range - Flash Mode
Spotlight mode set to 40% of Flash Current
3.0V to 5.25V Input Range
External Flash Control Pin for Synchronization to a
Camera Module or Graphics Controller
Short Circuit, Over-Voltage, and Over-Temperature
Protection
Soft-Start Functionality
Two Control Inputs for Maximum Versatility
Shutdown Current < 2
A
Micro Lead Package MLPD-10, 3mm x 3mm
Mobile Camera Phones
Digital Cameras
PDAs with Built-in Cameras
The SC615A 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 re-
quired to develop the output drive, providing a low EMI
solution compared to inductive boost regulators.
The SC615A has two modes of operation: Flash mode
and Spotlight mode. In Flash mode, the SC615A is ca-
pable of delivering 500mA of regulated current for a du-
ration of 500ms or up to 700mA for a reduced duration.
In Spotlight mode the SC615A 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
requirement of the SC615A. The flash input (FLASH)
overrides the control input (CTRL) to make sure the flash
function is activated when called for.
The thermally efficient MLPD-10 package and ceramic
bypass and bucket capacitors make the SC615A a high
output current driver that requires minimal PCB area.
Description
3.0V to 5.25V
SC615A
VIN
1
C2-
2
C2+
10
C1-
4
C1+
8
VOUT
9
FLASH
5
CTRL
7
GND
3
ISET
6
1
F
1
F
FLASH
CTRL
1
F
white LED
0.5
10
F
C1
C2
2
2005 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
SC615A
Notes:
1) Calculated from package in still air, mounted to 3"x 4.5", 4 layer FR4 PCB with thermal vias under the exposed pad per JESD51 standards.
2) Tested according to JEDEC standard JESD22-A114-B
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Absolute Maximum Ratings
Electrical Characteristics
Unless otherwise specified: T
A
= 25C for TYP, -40C to +60C for MIN and MAX;
C
BUCKET
= C
OUT
= 1.0F (ESR < 0.1
); C
IN
= 10.0F; V
IN
= 3.0V to 5.25V; V
OUT
= 2.8V to 4.25V; R
ISET
= 0.5
(0.1%).
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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.
5
2005 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
SC615A
Applications Information
General Operation
The SC615A is a powerful 2X charge pump designed to
drive a high-intensity white LED with a constant current
(Spotlight mode) or with a pulsed current of higher inten-
sity (Flash mode) used for camera flash.
In Flash mode the SC615A output can drive 500mA at
4.25V into an LED for a minimum duration of 500ms
under all temperature and input conditions. The FLASH
pin is used to trigger this mode (active high). In spotlight
mode the SC615A regulates the output current to 40%
of the Flash mode current setting when the CTRL pin is
pulled high and the FLASH pin is low. Note that Flash
mode has priority over Spotlight mode, i.e., the FLASH
pin triggers Flash mode regardless of the state of the
CTRL pin.
Output current is regulated by attaching the ISET pin to
the cathode(s) of the LED package and a low resistance
sense resistor (typically 0.5
). The ISET pin monitors
the voltage at the cathode and signals the charge pump
to increase or decrease the output current until the ISET
voltage reaches the programmed setting. The resistor
value is chosen to set the current through the LED based
on this reference voltage. The resistor can be chosen to
set either the flash mode current or spotlight mode cur-
rent, but it should not be less than 0.35
due to output
current limitations of the device.
Flash Mode
Flash mode is enabled whenever the FLASH pin is pulled
high and remains active until the FLASH pin is released.
This mode has higher priority than Spotlight mode, so
the state of the CTRL pin is overridden whenever the
FLASH pin is activated. While in flash mode the refer-
ence voltage on the ISET pin is set to 250mV. The dura-
tion of the pulse is limited by the amount of power that
can be dissipated in the SC615A before it exceeds the
maximum operating temperature. Note that if an output
current less than the rated 500mA is desired, the dura-
tion of the pulse can increase proportionally. However,
great care should be taken to insure the FLASH pin is
not held high for an extended amount of time so that
overheating does not occur. Extending flash mode be-
yond the 500ms pulse limit could adversely affect the
long term reliability of the SC615A. Flash duration must
be derated at higher currents, for example, 700mA
derates to a maximum of 350ms.
In flash mode, I
OUT
= 250mV/R
ISET
.
Spotlight Mode
Spotlight mode is enabled by setting the CTRL pin high
and keeping the FLASH pin low. When in Spotlight mode,
the SC615A can maintain a constant current indefinitely
to drive an LED or bank of LEDs. The ISET reference
voltage is set to 100mV so that the output current is
maintained at 200mA when a 0.5
resistor is used.
Spotlight current is always 40% of flash current for any
given value of R
ISET
.
In spotlight mode, I
OUT
= 100mV/R
ISET
.
Protection Circuitry
The SC615A also provides protection circuitry that pre-
vents the device from operating in an unspecified state.
These funtions include Input Over-Voltage Protection
(IOVP), Output Over-Voltage Protection (OVP), Over-Tem-
perature (OT) Protection, Over-Current Protection (OCP),
and Short-Circuit Current Protection (SCCP).
Input Over-Voltage Protection
Input over-voltage protection is included to prevent op-
eration at high input voltages that could damage the
device. The IOVP circuit senses the input voltage and
determines when the supply exceeds 6V. Hysteresis is
included in this circuit to avoid chattering between states.
When the voltage rises above this threshold, the device
is disabled until the input voltage drops to a level within
the specified range.
Output Over-Voltage Protection
Output over-voltage protection is included to prevent the
SC615A from generating an output voltage that could
damage other devices connected to it such as load LEDs
and bypass capacitors. When the output voltage exceeds
5.5V, the OVP circuit disables the charge pump until the
voltage decreases to a level within the acceptable range.
This circuit allows the device to drive LEDs with high for-
ward voltages at a reduced level without exceeding the
output voltage limits specified for the device. Note, how-
ever, that this effect is a consequence of the OVP circuit
and is not its intended purpose.
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