LTC3406AE View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC3406AE' PDF : 16 Pages View PDF
LTC3406A
APPLICATIONS INFORMATION
–
VOUT
+
COUT
L1
1
RUN
5
VFB
LTC3406A
2
GND
3 SW
VIN 4
CIN
R2
R1
CFWD
VIN
BOLD LINES INDICATE HIGH CURRENT PATHS
3406A F03
Figure 3. LTC3406A Layout Diagram
VOUT
VIA TO VIN
R1
PIN 1
L1 SW
LTC3406A
R2
CFWD
VIN
VIA TO VOUT
COUT
CIN
GND
Figure 4. LTC3406A Suggested Layout
3406A F04
Design Example
As a design example, assume the LTC3406A is used
in a single lithium-ion battery-powered cellular phone
application. The VIN will be operating from a 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),
L
=
(
1
f ) ( IL
)
VOUT
1
VOUT
VIN
(3)
Substituting VOUT = 2.5V, VIN = 4.2V, ∆IL = 240mA and
f = 1.5MHz in Equation (3) gives:
L
=
2.5V
1.5MHz(240mA)
1
2.5V
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 an RMS current rating of at least 0.3A ≅
ILOAD(MAX)/2 at temperature and COUT will require an ESR
of less than 0.25Ω. In most cases, a ceramic capacitor
will satisfy this requirement.
3406afa
12
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