cat4240 Catalyst Semiconductor, cat4240 Datasheet - Page 6

• Manufacturer Part Number: cat4240
• Description: 6 Watt Boost Led Driver
• Manufacturer: Catalyst Semiconductor

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.
SHDN
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.
SIMPLIFIED BLOCK DIAGRAM
Doc. No. MD-5026 Rev. C
¯¯¯¯¯ is the shutdown logic input. When the pin is
V
IN
Pin #
1
2
3
4
5
C1
SHDN
V
IN
Name
SHDN
¯¯¯¯¯
GND
SW
VIN
FB
Shutdown
Thermal
& UVLO
300mV
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.
Ref
–
+
Current
Sense
+
–
Oscillator
1MHz
+
–
6
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:
The lower LED cathode is connected to the FB pin.
Over Voltage
PWM
Logic
Protection
&
I
Driver
LED
= 0.3V/R1
R
SW
Characteristics subject to change without notice
S
GND
FB
© Catalyst Semiconductor, Inc.
Current
C2
V
LED
OUT
R1