CAT4240 Datasheet, PDF (8/12 Pages) Catalyst Semiconductor – 6 Watt Boost LED Driver

CAT4240
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 40 V. 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 6 mW (about 1.6 mA input current with a 3.6 V
supply). The SW pin clamps at a voltage below its maximum
rating of 60 V. There is no need to use an external zener diode
between Vout and the FB pin. A 50 V rated C₂ capacitor is
required to prevent any overvoltage damage in the open
LED condition.
V_L
13 V
C1
VIN
5V
ON _OFF
L
47 mH
4.7 mF
VIN
Schottky 100 V
(Central CMSH1−100)
VOUT
C2
1 mF
SW
CAT4240
SHDN
FB
GND
R1
3W
Figure 18. Open LED Protection without Zener
5.0
60
4.0
3.0
2.0
1.0
VIN = 5 V
0
8 9 10 11 12 13 14 15 16
INDUCTOR VOLTAGE (V)
Figure 19. Open LED Supply Current vs. V_IN without
Zener
55
50
45
40
8 9 10 11 12 13 14 15 16
INDUCTOR VOLTAGE (V)
Figure 20. Open LED Output Voltage vs. V_IN without
Zener
Figure 21. Open LED Disconnect and Reconnect
Figure 22. Open LED Disconnect
http://onsemi.com
8