BD60A00NUX Datasheet, PDF (11/23 Pages) Rohm – White Backlight LED Drivers for Small to Medium LCD Panels (Switching Regulator Type)

BD60A00NUX, BD60A60NUX
Technical Note
●Operating of the application deficiency
1) When 1 LED or 1string OPEN during the operating
Since FB terminal is set to 0V when set to OPEN, Output boosts up to the over voltage protection voltage. When over
voltage is detected, the boosting operation stops and then output voltage goes down slowly. Later, if output voltage
becomes less than hysteresis of over current protection, output voltage keeps boosting up to over voltage protection
voltage again.
Vout
Hysteresis voltage
FB
FB voltage
LED
connection
normal
Open
LED current 20mA
0mA
Fig. 8 LED open detect
2) When LED short-circuited in the plural
Even if one LED short-circuits during boost operation, it usually passes along LED and it is turned on. By making LED
shorted, FB terminal voltage increases by LED VF. Therefore output voltage becomes lower by LED VF, and the
condition turns to be normal.
output
FB
VOUT
LED short
FB _0.7V
LED current 20mA
VF of LED
0.7V+VF of LED
VF of LED
VOUT
FB
Fig. 9 One LED shorted
VOUT
LED short
VIN
5.9V
FB _0.7V
LED current 20mA
0.1mA
100uS
Fig.10 FB terminal – VOUT terminal shorted
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11/22
2011.12 - Rev.A