CAT4237 Datasheet, PDF (3/13 Pages) Catalyst Semiconductor – High Voltage CMOS Boost White LED Driver

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 (4.7uF) be placed between the VIN
and GND pins near the device. If the supply
voltage drops below 1.9V, the device stops
switching.
SHDN* 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
place on the PCB.
CAT4237
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 35V, 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
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.
BLOCK DIAGRAM
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
3 of 13
Doc. No. 5013, Rev. A