CAT4237 Datasheet, PDF (9/13 Pages) Catalyst Semiconductor – High Voltage CMOS Boost White LED Driver

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
Open LED Protection without Zener
CAT4237
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 Switching waveforms
without Zener
Open LED Supply Current vs. VIN
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. VIN
without Zener
50
45
40
35
30
2.5 3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE [V]
© 2005 Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
9 of 13
Doc. No. 5013, Rev. A