CAT4237TD-T3 Datasheet, PDF (3/14 Pages) ON Semiconductor – High Voltage CMOS Boost White LED Driver

CAT4237
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.
S¯¯H¯D¯N¯ 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.
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 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
S¯¯H¯D¯N¯
Shutdown pin (Logic Low). Set high to enable the driver.
5
VIN
Power Supply input.
BLOCK DIAGRAM
V_IN
C1
4.7µF
V_IN
SHDN
V_REF ^{300mV –}
+ ^A1
Enable
RC
Thermal
C_C
Shutdown
& UVLO
33µH
1MHz
Oscillator
+
A2
–
Current
Sense
SW
Over Voltage
Protection
PWM &
Logic
Driver
N1
R_S
C2
0.22µF
LED
Current
GND
FB
R1
15Ω
2008 SCILLC. All rights reserved.
3
Characteristics subject to change without notice
Doc. No. MD-5013, Rev. C