A8240
LED BACKLIGHT DRIVER
AiT Semiconductor Inc.
www.ait-ic.com
WLED LINEAR DRIVER FOR LI-ION BATTERY APPLICATION
DETAILED INFORMATION
A8240 works with a wide range of supply voltage, from 2.7V to 6V. The forward voltage of commercial
white/blue LED is in the range of 2.9V to 3.5V at a current level of 20mA. Proper selection of the LED to match
the supply voltage can fully utilize the Li-ion battery. For example, there is 1% ~ 3 % power left in the Li-ion
battery when its voltage reaches 3.275V. So a LED with a forward voltage value of 3.2V can use up to 99% of
the battery power under normal working condition. When the voltage of the battery drops below 3.2V, the
current through the LED (hence the brightness) starts to decrease.
Due to its uniquely designed current regulator, A8240 offer low output dropout and provide superior efficiency
performance over standard Inductive boost type and capacitive charge pump type LED driver.
The EN pin controls the on/off state of the device. A high level state turns on the device and a low level turns
off the device, results in the low off state current. This pin needs to be terminated since a floating level of the
EN pin will cause the instability of the device.
The sink current has a constant value of 20mA. The brightness of the LED can be adjusted by controlling the
duty cycle of the A8240’s LEDn output. This can be accomplished by applying a PWM signal to the EN pin. In
A8240, the internal power on sequence presents a delay time of 6us from EN pin to LEDn pin. Hence, In order
to normally modulate the output of LEDn in every cycle, the width of dimming signal applied EN pin have to be
no less than 6us. For example, when a dimming signal of 20KHz is applied, the minimum range of dimming is
about 12%, that is, the average output current on each channel is 2.4mA.
REV2.0
- NOV 2011 RELEASED, OCT 2014 UPDATED -
- 6 -
AITSEMI [ AiT Semiconductor ]
