W-6237 Datasheet, PDF (9/13 Pages) Copal Electronics – High Voltage CMOS Boost

W-6237
Open LED Protection
In the event of an “Open LED” fault condition, the
W-6237 will continue to boost the output voltage with
maximum power until the output voltage reaches
approximately 35 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 4 mW (about 1 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_IN
C₁
4.7 F
OFF _ON
L
33 H
Schottky 100 V
(Central CMSH1ï100)
V_OUT
C₂
SW
VIN
0.22 F
W-6237
SHDN
GND
V_FB = 300 mV
FB
R1
15
Figure 21. Open LED Protection without Zener
2.0
1.5
1.0
0.5
0
2.5
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE (V)
Figure 23. Open LED Supply Current vs. V_IN without
Zener
50
45
40
35
SW PIN
10 V/div
30
2.5
3.0
3.5
4.0
4.5
5.0
INPUT VOLTAGE (V)
Figure 24. Open LED Output Voltage vs. V_IN without
Zener
10 sec/div
Figure 22. Open LED Switching Waveforms without
Zener
9