cat4237 Catalyst Semiconductor, cat4237 Datasheet - Page 9

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

V
OPEN LED PROTECTION
In the event of an “Open LED” fault condition, the
CAT4237 will continue to boost the output voltage with
maximum power until the output voltage reaches
approximately 35V. Once the output exceeds this
level, the internal circuitry immediately places the
device into a very low power mode where the total
input power is limited to about 4mW (about 1mA input
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
IN
4.7µF
C
OFF ON
1
Open LED Protection without Zener
Open LED Supply Current vs. V
2.0
1.5
1.0
0.5
0.0
2.5
SHDN
VIN
3.0
without Zener
INPUT VOLTAGE [V]
33µH
CAT4237
L
GND
3.5
SW
FB
4.0
V
FB
Schottky 100V
(Central CMSH1-100)
= 300mV
4.5
C
0.22µF
R1
15Ω
2
IN
V
5.0
OUT
9
current with a 3.6V supply). The SW pin clamps at a
voltage below its maximum rating of 60V. There is no
need to use an external zener diode between Vout
and the FB pin. A 50V rated C
prevent any overvoltage damage in the open LED
condition.
Open LED Output Voltage vs. V
50
45
40
35
30
Open LED Switching waveforms
2.5
3.0
without Zener
without Zener
INPUT VOLTAGE [V]
3.5
2
capacitor is required to
4.0
Doc. No. MD-5013, Rev. B
4.5
CAT4237
IN
5.0