cat4237 Catalyst Semiconductor, cat4237 Datasheet - Page 3

• Manufacturer Part Number: cat4237
• Description: High Voltage Cmos Boost White Led Driver
• Manufacturer: Catalyst Semiconductor

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 place on the PCB.
PIN DESCRIPTIONS
BLOCK DIAGRAM
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
¯¯¯¯¯ is the shutdown logic input. When the pin is
V
Pin #
IN
1
2
3
4
5
4.7µF
C1
SHDN
V
SHDN
¯¯¯¯¯
IN
Name
GND
SW
VIN
FB
V
Shutdown
Thermal
& UVLO
REF
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.
Enable
300mV
+
–
A1
R C
C
C
Current
Sense
33µH
+
–
A2
Oscillator
3
1MHz
+
–
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:
The lower LED cathode is connected to the FB pin.
Over Voltage
PWM &
Logic
Protection
I
LED
Driver
= 0.3V/R
SW
N 1
R
S
1
GND
0.22µF
Doc. No. MD-5013, Rev. B
FB
Current
C2
LED
CAT4237
15Ω
R1