CAT4139 Datasheet, PDF (9/13 Pages) Catalyst 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 24 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 40 V. There is no need to use an external zener diode
between VOUT and the FB pin. A 35 V rated C2 capacitor
is required to prevent any overvoltage damage in the open
LED condition.
V_IN
C1
4.7 mF
OFF _ON
L
22 mH
Schottky 40 V
(Central CMSH05−4)
D
V_OUT
SW
VIN
CAT4139
SHDN
FB
GND
C2
1 mF
R1
15 W
Figure 18. Open LED Protection Circuit
Figure 19. Open LED Disconnect and Reconnect
2.5
Figure 20. Open LED Disconnect
35
30
2.0
25
1.5
20
1.0
15
3.0
3.5
4.0
4.5
5.0
5.5
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Figure 21. Open LED Supply Current
Figure 22. Open LED Output Voltage
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