BD6590MUV
Technical Note
●Operating of the application deficiency
1)When 1 LED or 1string OPEN during the operating
The LED string that became OPEN isn't lighting, but other LED strings are lighting.
Then LED terminal is 0V, output boosts up to the over voltage protection voltage. When over voltage is detected,
the feedback of open string isn’t returned, so that VOUT will return normal voltage.
In the case that the voltage of 2 LED terminals becomes more than 25V(Absolute maximum ratings) as VOUT boosts up to
the over voltage protection voltage, please pay attention carefully that 2 LED terminals could be broken up in setting over
voltage protection.
OVP setting when selecting terminals
Vout
Over voltage protection voltage
40
35
30
25
20
15
10
LED1 voltage
LED2 voltage
LED 1 connection normal
LED connection
open
normal
LED1
LED2
Setting range of over voltage protection
LED 1 feedback
PWMPOW, PWMDRV
LED 1current
return
off
return
5
0
20mA
0mA
LED Vf
(Vout)
10
20
30
40
LED 2 current
20mA
Fig.10 LED OPEN detect
Moreover, excessively high level of over voltage limit in terminal setting makes it happen that LED terminal voltage
exceeds LED terminal over voltage protect, which accordingly turn off LED lights. In order to prevent this problem, please
see “How to set the external resistor of over voltage limit (p.7)” and then set over voltage referring to application.
2) When LED short-circuited in the plural
All LED strings is turned on unless LED1~6 terminal voltage is more than 11.5V.
When it was more than 11.5V only the strings which short-circuited is turned off normally and LED current of other lines
continue to turn on.
LED terminal voltage
LED short
LED1 12.7V
LED short-circuited
40
35
30
0.7V
LED2
25
20
15
10
Vout
LED 1
LED 2
Voltage range of LED short-circuited
I LED1
20mA
20mA
0mA
5
0
I LED2
LED Vf
(Vout)
LED 1 FeedBack
normal
cut
10
20
30
40
Fig.11 LED short detect
3)When Schottky diode comes off
IC and a switching transistor aren't destroyed because boost operating stops by the Schottky diode coming off protected
function.
4)When the resistor of over current detection comes off
All the LEDs do not turn on due to open protect of the OCP resistor, which stops boost operation and consequently
prevents passing LED current.
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2011.07 - Rev.B
10/26
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