XC9116
Series
■APPLICATION
INFORMATION
<Dimming Control>
1. Applying PWM signal to the CE pin
The XC9116 repeats on/off operations by a PWM signal applied to the CE pin. The magnitude of LED current, I
LED
, when
the diode is on, is determined by R
LED
. The magnitude is zero when the diode is off. The average of LED current is
proportional to the positive duty ratio of the PWM signal.
The frequency of the PWM signal can be controlled to the optimum value between 100Hz and 10kHz. With regard to the
amplitude of the PWM signal, the high level should be higher than the "H" voltage of CE, V
CEH
, and the low level, lower
than the "L" voltage of CE, V
CEL
.
20µsec / div
20µsec / div
200µsec / div
200µsec / div
2. Step-Wise Regulation of LED Current
In some applications, it may be necessary to incorporate step-wise regulation of LED current, I
LED
. Step-wise regulation
of LED illumination is achieved by connecting a switch element SW1 in parallel with R
LED
and in series with R
LED1
and
turning SW1 on and off, as shown below. Choose a resistance of R
LED
so that the minimum necessary current is gained
when switch element SW1 is off. The resistance of R
LED1
should be such that a desired increase of current passed
through the LED is gained when the switch element is on.
L
VIN
SD
Ex.) Current I
LED
= 5mA and 15mA
R
LED
= 200mV / 5mA = 40
Ω
R
LED1
= 200mV / (15mA – 5mA) = 20
Ω
VIN
CIN
CE
ON/OFF
VSS
Lx
ILED
CL
FB
RLED
RLED1
signal
SW1
Figure : Circuit using Step-wise Regulation of LED Current
7/22
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