CAT4240 Datasheet, PDF (6/12 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 2.8 V and up to
5.5 V. It is recommended that a small bypass ceramic
capacitor (4.7 mF) be placed between the VIN and GND pins
near the device. If the supply voltage drops below 1.9 V, the
device stops switching.
SHDN is the shutdown logic input. When the pin is tied to
a voltage lower than 0.4 V, the device is in shutdown mode,
drawing nearly zero current. When the pin is connected to a
voltage higher than 1.5 V, 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 40 V,
the device enters a low power operating mode preventing the
SW voltage from exceeding the maximum rating.
FB feedback pin is regulated at 0.3 V. A resistor connected
between the FB pin and ground sets the LED current
according to the formula:
I_LED
+
0.3 V
R1
The lower LED cathode is connected to the FB pin.
Table 4. PIN DESCRIPTIONS
Pin #
Name
Function
1
SW
Switch pin. This is the drain of the internal power switch.
2
GND
Ground pin. Connect the pin to the ground plane.
3
FB
Feedback pin. Connect to the last LED cathode.
4
SHDN
Shutdown pin (Logic Low). Set high to enable the driver.
5
VIN
Power Supply input.
Simplified Block Diagram
V_IN
C1
Ref
300 mV
–
+
V_IN
SHDN
Thermal
Shutdown
& UVLO
SW
1 MHz
Oscillator
+
–
Current
Sense
Over Voltage
Protection
PWM
&
Logic
Driver
R_S
Figure 17. Simplified Block Diagram
V_OUT
C2
LED
Current
GND
FB
R1
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