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 m F) 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
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:
connected directly to the ground plane on the PCB.
I LED +
0.3 V
R1
The lower LED cathode is connected to the FB pin.
Table 4. PIN DESCRIPTIONS
Pin #
1
2
3
4
5
Name
SW
GND
FB
SHDN
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
SW
V OUT
C2
Ref
300 mV
1 MHz
Oscillator
Over Voltage
Protection
V IN
SHDN
Thermal
Shutdown
& UVLO
+
+
PWM
&
Logic
Driver
R S
LED
Current
GND
Current
Sense
FB
R1
Figure 17. Simplified Block Diagram
http://onsemi.com
6
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