SC615
POWER MANAGEMENT
Applications Information
Spotlight Mode
Spotlight mode is enabled by setting the CTRL pin high
and keeping the FLASH pin low. When in Spotlight mode,
the SC615 can maintain a constant current indefinitely
to drive an LED or bank of LEDs. The ISET reference
voltage is set to 50mV so that the output current is main-
In Flash mode the SC615 output can drive 500mA at tained at 100mA when a 0.5Ω resistor is used.
4.25V into an LED for a minimum duration of 500ms.
The FLASH pin is used to trigger this mode (active high).
Protection Circuitry
In spotlight mode the SC615 regulates the output cur- The SC615 also provides protection circuitry that pre-
rent to 100mA when the CTRL pin is pulled high and the vents the device from operating in an unspecified state.
FLASH pin is low. Note that Flash mode has priority over These funtions include Input Over-Voltage Protection
Spotlight mode, i.e., the FLASH pin triggers Flash mode (IOVP), Output Over-Voltage Protection (OVP), Over-Tem-
regardless of the state of the CTRL pin.
perature (OT) Protection, Over-Current Protection (OCP),
and Short-Circuit Current Protection (SCCP).
Output current is regulated by attaching the ISET pin to
the cathode(s) of the LED package and a low resistance
Input Over-Voltage Protection
sense resistor (typically 0.5Ω). The ISET pin monitors Input over-voltage protection is included to prevent op-
the voltage at the cathode and signals the charge pump eration at high input voltages that could damage the
to increase or decrease the output current until the ISET device. The IOVP circuit senses the input voltage and
voltage reaches the programmed setting. The resistor determines when the supply exceeds 6V. Hysteresis is
value is chosen to set the current through the LED based included in this circuit to avoid chattering between states.
on this reference voltage. The resistor can be chosen to When the voltage rises above this threshold, the device
set either the flash mode current or spotlight mode cur- is disabled until the input voltage drops to a level within
rent, but it should not be less than 0.5Ω due to output the specified range.
current limitations of the device.
Output Over-Voltage Protection
Flash Mode
Output over-voltage protection is included to prevent the
Flash mode is enabled whenever the FLASH pin is pulled SC615 from generating an output voltage that could dam-
high and remains active until the FLASH pin is released. age other devices connected to it such as load LEDs and
This mode has higher priority than Spotlight mode, so bypass capacitors. When the output voltage exceeds
the state of the CTRL pin is overridden whenever the 5.5V, the OVP circuit disables the charge pump until the
FLASH pin is activated. While in flash mode the refer- voltage decreases to a level within the acceptable range.
ence voltage on the ISET pin is set to 250mV. The dura-
tion of the pulse is limited by the amount of power that This circuit allows the device to drive LEDs with high for-
can be dissipated in the SC615 before it exceeds the ward voltages at a reduced level without exceeding the
maximum operating temperature. Note that if an output output voltage limits specified for the device. Note, how-
current less than the rated 500mA is desired, the dura- ever, that this effect is a consequence of the OVP circuit
tion of the pulse can increase proportionally. However, and is not its intended purpose.
great care should be taken to insure the FLASH pin is
not held high for an extended amount of time so that
Over-Temperature Protection
overheating does not occur.
Extending flash mode be- The over-temperature circuit helps prevent the device
yond the 500ms pulse limit could adversely affect the from overheating and experiencing a catastrophic fail-
long term reliability of the SC615.
ure. When the junction temperature exceeds 150°C the
device is disabled. It remains disabled until the junction
temperature drops below this threshold. As with the UVLO
and OVP circuits, hysteresis is included to prevent tog-
gling between modes.
2005 Semtech Corp.
5
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General Operation
The SC615 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.
SEMTECH [ SEMTECH CORPORATION ]
