CAT4137 Datasheet, PDF (12/16 Pages) Catalyst Semiconductor – CMOS Boost Converter - White LED Driver

CAT4137
OPEN LED PROTECTION
In the event of an “Open LED” fault condition, the
CAT4137 will continue to boost the output voltage
with maximum power until the output voltage reaches
approximately 24V. Once the output exceeds this
level, internal circuitry immediately places the device
into a very low power mode where the total input
power consumed is less than 10mW.
In low power mode, the input supply current will
typically drop to 2mA. An internal clamping circuit will
limit the subsequent output voltage to approximately
29V. This operating mode eliminates the need for any
external protection zener diode. This protection
scheme also fully protects the device against any
malfunction in the external Schottky diode (open-
circuit).
Open LED Protection
V_IN
C1
1µF
OFF ON
(Central CMDSH2-3)
L
D
V_OUT
22µH
C2
SW
VIN
0.22µF
CAT4137
SHDN
FB ^{VFB = 300mV}
R1
GND
15Ω
Open LED Power-up Waveforms
Open LED Supply Current vs. VIN
2.5
2.0
1.5
1.0
2.5 3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE [V]
Doc. No. MD-5012 Rev. B
12
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice