CAT4139TD-GT3 Datasheet, PDF (8/13 Pages) ON Semiconductor – 22V High Current Boost White LED Driver

CAT4139
OPEN LED PROTECTION
In the event of an “Open LED” fault condition, the
CAT4139 will continue to boost the output voltage
with maximum power until the output voltage
reaches approximately 24V. 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 40V. There is no need to use an external
zener diode between VOUT and the FB pin. A 35V
rated C2 capacitor is required to prevent any
overvoltage damage in the open LED condition.
Open LED Protection Circuit
Schottky 40V
(Central CMSH05-4)
V_IN
C1
L
22µH
D
V_OUT
C2
4.7µF
SW
1µF
VIN
CAT4139
OFF ON SHDN FB
R1
GND
15Ω
Open LED Supply Current
2.5
2.0
1.5
1.0
3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE [V]
Open LED Disconnect and Reconnect
Open LED Disconnect
Open LED Output Voltage
35
30
25
20
15
3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE [V]
Doc. No. MD-5032 Rev. B
8
© 2008 SCILLC. All rights reserved.
Characteristics subject to change without notice