YB1303
Low Dropout LED Driver
Example 1:
Drive low V
F
white or blue LEDs directly
from single cell Li-Ion battery
When using white or blue low V
F
LEDs,
and utilizing the driver’s low voltage drop,
only 3.4V in V
IN
is needed for the full 20mA
LED current. At 3.2V, there is still 5mA
typical current available for the LEDs. The
single cell Li-Ion battery is utilized in many
applications like cell-phones and digital still
cameras. In most cases, the Li-Ion battery
voltage level only goes down to 3V, and not
down to the full discharged level (2.7V)
before requesting the charger.
Example 2:
Drive high VF white or blue LEDs from
exiting bus from 4.0V to 6V
High V
F
white or blue LEDs have forward
voltage drop in the range of 3.2V to 4.0V.
To drive these LEDs with the maximum
current of 20mA for maximum brightness,
usually requires a boost circuit for a single
cell Li-Ion voltage range. In some cases,
there is already a voltage bus in the system,
which can be utilized. Due to the ultra-low
voltage drop of the YB1303 to drive high V
F
white or blue LEDs, the V
IN
needs to be
only 300mV higher than the highest V
F
in
the circuit.
-V
DROP
< 0.3V
-V
F
(@20mA) < 3.1V (Low V
F
)
-V
IN
(@20mA) = -V
DROP
+V
F
=3.4V
-V
IN
(@5mA typical) ~3.1V
Where V
IN
= Single cell Li-Ion Voltage
Key advantages:
No boost circuit needed for the LCD or
keyboard backlight.
Drivers directly connected to a Li-Ion
battery.
No EMI, no switching noise, no boost
efficiency lost, no capacitor and no
inductor.
YB1303 Rev.1.0
-V
DROP
< 0.3V
-V
F
(@20mA) < 3.3V to 4.0V (High V
F
)
-V
IN
(@20mA) = -V
DROP
+V
F
=3.6V to 4.3V
-V
IN
(@5mA typical) ~3.3V
Where V
IN
= Existing bus = 3.3V to 4.3V
Key advantages:
No boost circuit needed for the LCD or
keyboard backlight.
Driver utilizes the existing bus.
Ultra-low voltage drop provides the full
20mA LED current at the lowest possible
voltage level.
6
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YOBON [ YOBON TECHNOLOGIES,INC. ]
