W-6238 Datasheet, PDF (9/14 Pages) Copal Electronics – High Efficiency 10 LED Boost Converter

W-6238
OPEN LED PROTECTION
In the event of an “Open LED” fault condition, the
W-6238 will continue to boost the output voltage with
maximum power until the output voltage reaches
approximately 40V. 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 60V. There is
no need to use an external zener diode between Vout
and the FB pin. A 50V rated C2 capacitor is required
to prevent any overvoltage damage in the open LED
condition.
VIN
C1
Open LED Protection without Zener
Schottky 100V
L
(Central CMSH1-100)
47µH
V_OUT
C2
4.7µF
SW
VIN
0.22µF
OFF ON
W-6238
SHDN
FB ^{VFB = 300mV}
GND
R1
15Ÿ
Open LED Switching Waveforms
without Zener
Open LED Supply Current vs. VIN
without Zener
5.0
4.0
3.0
2.0
1.0
0.0
3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE [V]
Open LED Output Voltage vs. VIN
without Zener
55
50
45
40
35
3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE [V]
© NIDEC COPAL ELECTRONICS CORP.
9
Characteristics subject to change without notice
Doc. No. MD-5019 Rev. D