XC9116
Series
■APPLICATION
INFORMATION (Continued)
<LED Open-circuit Protection>
If white LEDs are opened or damaged, the FB pin is pulled down, so that the operating duty ratio reaches the maximum.
Accordingly, the output voltage continues to increase, possibly causing the Lx pin voltage to exceed the absolute
maximum rating of 22V.
In the case of the B type products, if white LEDs are opened or damaged, the detector built in the Lx pin causes the IC to
stop oscillating, preventing excessive increase of the output voltage. However, the detector may detect an overvoltage if
the Lx pin voltage exceeds 18V, which is the overvoltage limit, even when no LEDs are open. Therefore, care must be
taken if four LEDs each having a forward voltage of 4.45V or more are connected in series.
In the case of the D type products (no overvoltage limit circuit), a Zener diode (ZD) and a resistor (R1) can be externally
connected to serve as a load in the case that LEDs are opened, preventing the increase of the Lx pin voltage. The ZD
voltage should be set to no more than 20V and no less than the product of each white LED’s maximum forward voltage
multiplied by the number of the connected LEDs, so that the Zener diode will not load the LEDs during normal operation.
If the Zener diode becomes load, the current that runs through the white LEDs is reduced, decreasing illumination.
L:22uF
VLF3010A
VIN
2.5V~6.0V
ZD
MAZ8180
CIN
4.7uF
VIN
Lx
R1
CE
VSS
FB
100Ω
R LED
10Ω
CL
0.22uF
SBD
XB0ASB03A1B
20mA
Note : The XC9116B02A series requires neither the Zener diode (ZD) nor the resistor 1 (R1).
<Startup Inrush Current>
The XC9116 series has no soft-start circuit built-in in order to minimize delay at startup. The inrush current can reach up
to the current limit, I
LIM
.
In some cases, overshoot can occur.
10/22
TOREX [ TOREX SEMICONDUCTOR ]
