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參數(shù)資料
| 型號(hào)： | SC615 |
| 廠商： | Semtech Corporation |
| 英文描述： | Charge Pump Flash LED Driver |
| 中文描述： | 電荷泵閃光LED驅(qū)動(dòng)器 |
| 文件頁(yè)數(shù)： | 5/12頁(yè) |
| 文件大?。?/td> | 212K |
| 代理商： | SC615 |
5
2005 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
Applications Information
SC615
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.
In Flash mode the SC615 output can drive 500mA at
4.25V into an LED for a minimum duration of 500ms.
The FLASH pin is used to trigger this mode (active high).
In spotlight mode the SC615 regulates the output cur-
rent to 100mA 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 0.5
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 SC615 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 SC615.
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-
tained at 100mA when a 0.5
resistor is used.
Protection Circuitry
The SC615 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
SC615 from generating an output voltage that could dam-
age 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.
Over-Temperature Protection
The over-temperature circuit helps prevent the device
from overheating and experiencing a catastrophic fail-
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.
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