BD8381EFV-M
Technical Note
・LED Short Detection
When the voltage between LEDR-pin and LEDC-pin 0.2 (TYP), the internal counter starts operating, and approximately
after 100ms (when FOSC = 300kHz) the operation latches off. With the PWM brightness control, the detecting operation
is processed only when PWMOUT-pin = High. If the condition of the detection operation is released before 100ms (when
FOSC = 300kHz), then the internal counter resets.
There is a possibility that the LED short detection malfunctions when the difference of Vf is large. Therefore, please
adjust external resistance for connected Vf. It is recommended 2V-3V to the input range of LEDR and LEDC.
※The counter frequency is the DCDC switching frequency determined by the RT. The latch proceeds at the count of 32770.
○High luminance LED (multichip) with built-in LED of X piece in 1chip when using Y piece
VOUT(DC/DC output)
Y piece
X piece
PWMOUT
FB
R3
LEDR
R4
R1
LEDC
R2
Setting method
R1:R2 = X:1
R3:R4 = ( X + 1 ) Y – 1:1
Fig. 15
○When using the single chip
VOUT(DC/DC output)
Y piece
PWMOUT
R3
LEDR
R4
R1
LEDC
R2
FB
Fig. 16
Setting method
R1:R2 = 1:1
R3:R4 = 2Y – 1:1
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2011.04 - Rev.A