cat4240 Catalyst Semiconductor, cat4240 Datasheet - Page 9

• Manufacturer Part Number: cat4240
• Description: 6 Watt Boost Led Driver
• Manufacturer: Catalyst Semiconductor

OPEN LED PROTECTION
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
VIN
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.
13V
ON OFF
5V
V
L
4.7µF
Open LED Supply Current vs. VIN
Open LED Protection without Zener
5.0
4.0
3.0
2.0
1.0
0.0
C1
8
9
INDUCTOR VOLTAGE [V]
without Zener
SHDN
VIN
10 11 12 13 14 15 16
CAT4240
47µH
GND
L
SW
FB
VIN = 5V
Schottky 100V
(Central CMSH1-100)
C2
1µF
R1
3Ω
VOUT
9
Open LED Disconnect and Reconnect
Open LED Output Voltage vs. VIN
60
55
50
45
40
8
Open LED Disconnect
9
INDUCTOR VOLTAGE [V]
without Zener
10 11 12 13 14 15 16
Doc. No. MD-5026 Rev. C
CAT4240