BL8580/1
■
DETAILED DESCRIPTION
BL8580/1 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, BL8580/1 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
BL8580/1’s LEDn output. This can be
accomplished by applying a PWM signal to
the EN pin. In BL8580/1, the internal power
on sequence presents a delay time of 6us
from CE pin to LEDn pin. Hence, In order to
normally modulate the output of LEDn in
every cycle, the width of dimming signal
applied CE 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 2.4 mA.
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