CAT4240_0711 Datasheet, PDF (7/14 Pages) Catalyst Semiconductor – 6 Watt Boost LED Driver

DEVICE OPERATION
The CAT4240 is a fixed frequency (1MHz), low noise,
inductive boost converter that provides a constant
current with excellent line and load regulation. The
device uses a high-voltage CMOS power switch
between the SW pin and ground to energize the
inductor. When the switch is turned off, the stored
energy in the inductor is released into the load via the
Schottky diode.
The on/off duty cycle of the power switch is internally
adjusted and controlled to maintain a constant
regulated voltage of 0.3V across the feedback resistor
connected to the feedback pin (FB). The value of the
resistor sets the LED current accordingly (0.3V/R1).
During the initial power-up stage, the duty cycle of the
internal power switch is limited to prevent excessive
in-rush currents and thereby provide a “soft-start”
mode of operation.
CAT4240
When the inductor is connected to a 9V supply or
higher, the CAT4240 can drive 6 LEDs in series at
300mA delivering a total power of 6 Watts into the
load. A separate 5V supply voltage is connected to
the VIN pin.
In the event of an “Open LED” fault condition, where
the feedback control loop becomes open, the output
voltage will continue to increase. Once this voltage
exceeds 40V, an internal protection circuit will become
active and place the device into a very low power safe
operating mode.
Thermal overload protection circuitry has been included
to prevent the device from operating at unsafe junction
temperatures above 150ºC. In the event of a thermal
overload condition the device will automatically
shutdown and wait till the junction temperatures cools
to 130ºC before normal operation is resumed.
© Catalyst Semiconductor, Inc.
7
Characteristics subject to change without notice
Doc. No. MD-5026 Rev. C