CAT4137 Datasheet, PDF (13/16 Pages) Catalyst Semiconductor – CMOS Boost Converter - White LED Driver

CAT4137
Open LED Protection
In the event of an “Open LED” fault condition, the
CAT4137 will continue to boost the output voltage with
maximum power until the output voltage reaches
approximately 24 V. Once the output exceeds this level,
internal circuitry immediately places the device into a very
low power mode where the total input power consumed is
less than 10 mW.
V_IN
C1
1 μF
OFF _ON
(Central CMDSH2−3)
L
D
V_OUT
22 μH
SW
VIN
C2
0.22 μF
CAT4137
SHDN FB
GND
V_FB = 300 mV
R1
15 W
In low power mode, the input supply current will typically
drop to 2 mA. An internal clamping circuit will limit the
subsequent output voltage to approximately 29 V. This
operating mode eliminates the need for any external
protection zener diode. This protection scheme also fully
protects the device against any malfunction in the external
Schottky diode (open-circuit).
Figure 31. Open LED Protection
2.5
Figure 32. Open LED Power−up Waveforms
2.0
1.5
1.0
2.5
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE (V)
Figure 33. Open LED Supply Current vs. VIN
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