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

CAT4240
PIN DESCRIPTION
VIN is the supply input for the internal logic. The
device is compatible with supply voltages down to
2.8V and up to 5.5V. It is recommended that a small
bypass ceramic capacitor (4.7μF) be placed between
the VIN and GND pins near the device. If the supply
voltage drops below 1.9V, the device stops switching.
S¯¯H¯D¯N¯ is the shutdown logic input. When the pin is
tied to a voltage lower than 0.4V, the device is in
shutdown mode, drawing nearly zero current. When
the pin is connected to a voltage higher than 1.5V, the
device is enabled.
GND is the ground reference pin. This pin should be
connected directly to the ground plane on the PCB.
SW pin is connected to the drain of the internal CMOS
power switch of the boost converter. The inductor and
the Schottky diode anode should be connected to the
SW pin. Traces going to the SW pin should be as
short as possible with minimum loop area. An over-
voltage detection circuit is connected to the SW pin.
When the voltage reaches 40V, the device enters a
low power operating mode preventing the SW voltage
from exceeding the maximum rating.
FB feedback pin is regulated at 0.3V. A resistor
connected between the FB pin and ground sets the
LED current according to the formula:
I_LED = 0.3V/R1
The lower LED cathode is connected to the FB pin.
Pin #
1
2
3
4
5
Name
SW
GND
FB
S¯¯H¯D¯N¯
VIN
Function
Switch pin. This is the drain of the internal power switch.
Ground pin. Connect the pin to the ground plane.
Feedback pin. Connect to the last LED cathode.
Shutdown pin (Logic Low). Set high to enable the driver.
Power Supply input.
SIMPLIFIED BLOCK DIAGRAM
V_IN
C1
Ref
300mV
–
+
V_IN
SHDN
Thermal
Shutdown
& UVLO
1MHz
Oscillator
+
–
Current
Sense
SW
Over Voltage
Protection
PWM
&
Logic
Driver
V_OUT
C2
LED
Current
R_S
GND
FB
R1
Doc. No. MD-5026 Rev. C
6
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice