A8180
AiT Semiconductor Inc.
www.ait-ic.com
LED LIGHTING DRIVER
HIGH BRIGHTNESS LED DRIVER WITH INTERNAL SWITCH
The average output current is given by:
ADJ (0.3V≤VADJ≤1.2V)
0.1xV
1.2xR
IOUT
=
S
Note that 100% brightness setting corresponds to: (1.3V≤VADJ≤5V)
Output Current Adjustment by PWM Control
A Pulse Width Modulated (PWM) signal with duty cycle PWM can be applied to the ADJ pin, as shown below,
to adjust the output current to a value below the nominal average value set by resistor RS:
0.1xD
IOUT
=
(0≤D≤100%, 1.2V≤VADJ≤5V)
RS
V
PULSEx0.1xD
IOUT
=
(0≤D≤100%, 0.3V≤VPULSE≤1.2V)
1.2xR
S
PWM dimming provides reduced brightness by modulating the LED’s forward current between 0% and
100%.The LED brightness is controlled by adjusting the relative ratios of the on time to the off time. A 25%
brightness level is achieved by turning the LED on at full current for 25% of one cycle. To ensure this
switching process between on and off state is invisible by human eyes, the switching frequency must be
greater than 100 Hz. Above 100 Hz, the human eyes average the on and off times, seeing only an effective
brightness that is proportional to the LED’s on-time duty cycle. The advantage of PWM dimming is that the
REV3.0
- APR 2010 RELEASED, JAN 2017 UPDATED -
- 12 -
AITSEMI [ AiT Semiconductor ]
