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PDF ML0308A Data sheet ( Hoja de datos )
| Número de pieza | ML0308A | |
| Descripción | White LED Driver and Step-up DC/DC Converter | |
| Fabricantes | Minilogic Device | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de ML0308A (archivo pdf) en la parte inferior de esta página. Total 9 Páginas | ||
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ML0308 Preliminary
______________________________________________________________________________________________________
ML0308A/B - Tiny Package, High Efficiency,
White LED Driver and Step-up DC/DC Converter
FEATURES
1.2MHz Switching Frequency Furnishes the
Use of Tiny Surface Mount Components
High Output Voltage: Up To 16V
Automatic Softstart
Drives Up To Four White LEDs From 3.6V
Supply
APPLICATIONS
LCD Bias
Handheld Computers
Battery Backup
Digital Cameras
DESCRIPTION
The ML0308 are high efficiency, white LED
driver and step-up DC/DC converters in a tiny
SOT23 5-lead package. The ML0308 switches
at 1.2MHz. High switching frequency permits
the use of tiny, low profile inductors and
capacitor to minimize footprint and cost in
space-conscious portable applications.
The 18V switch allows high output voltage up
to 16V to be easily generated in a simple boost
topology avoiding the use of costly
transformers.
TYPICAL APPLICATIONS
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Figure 1: One-cell Li-ion to 15V Converter and White LED Driver
1/9
Rev. B, July 2005
Datasheet pdf - http://www.DataSheet4U.co.kr/
1 page  
ML0308 Preliminary
______________________________________________________________________________________________________
APPLICATION INFORMATION
Choosing an Inductor
Several recommended inductors that work well
with the ML0308. Consult each manufacturer for
more detailed information and for their entire
selection of related parts. Many different sizes and
shapes are available. Use the equations and
recommendations in the next few sections to find
the correct inductance value for your design.
Inductor Selection—Boost Regulator
The formula below calculates the appropriate
inductor value to be used for a boost regulator
using the ML0308 (or at least provides a good
starting point). This value provides a good
tradeoff in inductor size and system performance.
Pick a standard inductor close to this value. A
larger value can be used to slightly increase the
available output current, but limit it to around
twice the value calculated below, as too large of
an inductance will increase the output voltage
ripple without providing much additional output
current. A smaller value can be used (especially
for systems with output voltages greater than 12V)
to give a smaller physical size. Inductance can be
calculated as:
L
=
V
OUT
−
V
IN
(
MIN
)
I
+
V
D
t
OFF
LIMIT
where VD = 0.4V (Schottky diode voltage), ILIMIT
= 180mA, and tOFF = 250ns; for designs with
varying VIN such as battery powered applications,
use the minimum VIN value in the above equation.
For most systems with output voltages below 7V,
a 4.7uH inductor is the best choice, even though
the equation above might specify a smaller value.
This is due to the inductor current overshoot that
occurs when very small inductor values are used
5/9
(see Current Limit Overshoot section). For higher
output voltages, the formula above will give large
inductance values. For a 3V to 16V converter
(typical LCD Bias application), a 22uH inductor is
called for with the above equation, but a 10uH
inductor could be used without excessive
reduction in maximum output current.
Current Limit Overshoot
For a fixed duty ratio PFM control scheme of the
ML0308, the power switch is turned off after 3/4
of a cycle or the 180mA current limit is reached.
There is a 100ns delay between the time when the
current limit is reached and when the switch
actually turns off. During this delay, the inductor
current exceeds the current limit by a small
amount. The peak inductor current can be
www.DataSheet.net/
calculated by
I
PEAK
=
I
LIMIT
+
V
IN
(
MAX
)−
L
V
DSSAT
td
Where VDSSAT = 0.25V (switch saturation voltage)
and td = 100ns. The current overshoot will be most
evident for systems with high input voltages and
for systems where smaller inductor values are
used. This overshoot can be beneficial as it helps
increase the amount of available output current for
smaller inductor values. This will be the peak
current seen by the inductor (and the diode) during
normal operation. For designs using small
inductance values (especially at input voltages
greater than 5V), the current limit overshoot can
be quite high. Although it is internally current
limited to 180mA, the power switch of the
ML0308 can handle larger currents without
problem, but the overall efficiency will suffer.
Rev. B, July 2005
Datasheet pdf - http://www.DataSheet4U.co.kr/
5 Page | ||
| Páginas | Total 9 Páginas | |
| PDF Descargar | [ Datasheet ML0308A.PDF ] | |
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