CAT4237_07 Datasheet, PDF (9/14 Pages) Catalyst Semiconductor – High Voltage CMOS Boost White LED Driver

CAT4237
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
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 C₂ capacitor is required to
prevent any overvoltage damage in the open LED
condition.
Open LED Protection without Zener
V_IN
C₁
4.7µF
OFF ON
L
33µH
Schottky 100V
(Central CMSH1-100)
V_OUT
C₂
SW
VIN
0.22µF
CAT4237
SHDN
FB ^{VFB = 300mV}
GND
R1
15Ω
Open LED Switching waveforms
without Zener
Open LED Supply Current vs. V_IN
without Zener
2.0
1.5
1.0
0.5
0.0
2.5 3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE [V]
Open LED Output Voltage vs. V_IN
without Zener
50
45
40
35
30
2.5 3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE [V]
© 2007 Catalyst Semiconductor, Inc.
9
Characteristics subject to change without notice
Doc. No. 5013, Rev. A