CAT4240 Datasheet, PDF (9/14 Pages) Catalyst Semiconductor – 6 Watt Boost LED Driver

OPEN LED PROTECTION
In the event of an “Open LED” fault condition, the
CAT4240 will continue to boost the output voltage
with maximum power until the output voltage
reaches approximately 40V. 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 6mW (about
1.6mA 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.
CAT4240
Open LED Disconnect and Reconnect
Open LED Protection without Zener
V_L
13V C1
4.7µF
VIN
5V
ON OFF
Schottky 100V
L
(Central CMSH1-100)
47µH
SW
VIN
CAT4240
VOUT
C2
1µF
SHDN
FB
GND
R1
3Ω
Open LED Supply Current vs. VIN
without Zener
5.0
4.0
3.0
2.0
1.0
0.0
8
VIN = 5V
9 10 11 12 13 14 15 16
INDUCTOR VOLTAGE [V]
Open LED Disconnect
Open LED Output Voltage vs. VIN
without Zener
60
55
50
45
40
8
9 10 11 12 13 14 15 16
INDUCTOR VOLTAGE [V]
© Catalyst Semiconductor, Inc.
9
Characteristics subject to change without notice
Doc. No. MD-5026 Rev. B