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Rev. E, Sep 2005
ML3406
Application Information (5)
Design Example
As a design example, assume the ML3406 is used in a
single Lithium - on battery – powered cellular phone
application. The VIN will be operation from maximum of
4.2V down to about 2.7V. The load current requirement is
a maximum of 0.6A but most of the time it will be in
standby mode, requiring only 2mA. Efficiency at both low
and high load currents is important. Output voltage is 2.5V.
With this information we can calculate L using equation
(1),
1
VOUT
L =
(f) (
IL)
VOUT ( 1-
VIN
)
(3)
Substituting VOUT = 2.5V, VIN = 4.2V,
IL = 240mA and f
=1.5MHz in equation (3) gives:
2.5V
2.5V
L =
1.5MHz (240mA)
( 1-
4.2V
) = 2.81µH
A 2.2µH inductor works well for this application. For best
efficiency choose a 720mA or greater inductor with less
than 0.2Ω series resistance
CIN will require and RMS current rating of at least 0.3A≒
ILOAD(MAX) / 2 at temperature and COUNT will require and ESR
of less than 0.25Ω. In most cases, a ceramic capacitor will
satisfy this requirement.
For the feedback resistors, choose R1=316k. R2 can then
be calculated from equation (2) to be:
VOUT
R2 =
(
0.6
- 1) R1 = 1000k
Figure 11
Recommend Components
Component
Rating
Item
Maker
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LQH32CN2R2M33
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LQH32CN2R7M34
Murata
Cin=2.2uF Ceramic
LMK212BJ225MG
Cin=4.7uF Ceramic
JMK212BJ475MG
Cin=10uF Ceramic
JMK316BJ106ML
Tayo Yuden
Capacitor
Cin=100uF Ceramic
4TPB100M
Sanyo POSCAP
ML3406