ltc3406ab-2 Linear Technology Corporation, ltc3406ab-2 Datasheet - Page 12

• Manufacturer Part Number: ltc3406ab-2
• Description: 2.25mhz, 600ma Synchronous Step-down Regulator In Thinsot
• Manufacturer: Linear Technology Corporation

LTC3406AB-2
APPLICATIONS INFORMATION
Design Example
As a design example, assume the LTC3406AB-2 is used
in a single lithium-ion battery-powered cellular phone
application. The V
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. Effi ciency at both
low and high load currents is important. Output voltage
is 2.5V. With this information we can calculate L using
Equation (1),
12
L
=
( )
f
( )
1
Δ
I
L
V
OUT
IN
will be operating from a maximum of
⎛
⎜
⎝
1
−
V
OUT
V
V
OUT
IN
⎞
⎟
⎠
L1
V
OUT
BOLD LINES INDICATE HIGH CURRENT PATHS
SW
PIN 1
Figure 4. LTC3406AB-2 Suggested Layout
–
+
Figure 3. LTC3406AB-2 Layout Diagram
C
OUT
VIA TO V
C
OUT
L1
LTC3406AB-2
IN
GND
1
2
3
(3)
LTC3406AB-2
RUN
SW
GND
C
IN
R1
V
V
C
Substituting V
f = 2.25MHz in Equation (3) gives:
A 2.2μH inductor works well for this application. For best
effi ciency choose a 720mA or greater inductor with less
than 0.2Ω series resistance.
C
I
of less than 0.25Ω. In most cases, a ceramic capacitor
will satisfy this requirement.
FB
IN
LOAD(MAX)
IN
IN
L
5
4
will require an RMS current rating of at least 0.3A ≅
C
=
R2
FWD
2 25
.
R2
/2 at temperature and C
MHz
2 5
OUT
.
3406AB2 F03
C
(
FWD
240
V
3406AB2 F04
V
= 2.5V, V
IN
mA
R1
V
+
–
IN
)
VIA TO V
⎛
⎝ ⎜
1
−
IN
OUT
2 5
4 2
= 4.2V, ΔI
.
.
V
V
OUT
⎞
⎠ ⎟
=
will require an ESR
1 87
.
L
= 240mA and
μ
H
3406ab2f