LTC3405A-1.8 Linear Technology, LTC3405A-1.8 Datasheet - Page 11

• Manufacturer Part Number: LTC3405A-1.8
• Description: 1.5V / 1.8V / 1.5MHz - 300mA Synchronous Step-Down Regulators in ThinSOT
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of the
LTC3405A series parts. These items are also illustrated
graphically in Figures 4 and 5. Check the following in your
layout:
1. The power traces, consisting of the GND trace, the SW
2. Does the (+) plate of C
3. Keep the (–) plates of C
Design Example
As a design example, assume the LTC3405A-1.8 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 0.25A but most of the time it will be in
trace and the V
wide.
possible? This capacitor provides the AC current to the
internal power MOSFETs.
Figure 4. LTC3405A-1.8 Layout Diagram
V
OUT
–
+
BOLD LINES INDICATE HIGH CURRENT PATHS
IN
IN
C
U
trace should be kept short, direct and
OUT
will be operating from a maximum of
L1
IN
1
2
3
U
IN
and C
RUN
SW
LTC3405A-1.8
GND
connect to V
MODE
OUT
V
OUT
C
V
W
IN
IN
as close as possible.
6
5
4
IN
as closely as
3405A1518 F04
V
U
IN
standby mode, requiring only 2mA. Efficiency at both low
and high load currents is important. Output voltage is
1.8V. With this information we can calculate L using
equation (1),
Substituting V
f = 1.5MHz in equation (3) gives:
For best efficiency choose a 300mA or greater inductor
with less than 0.3 series resistance.
C
I
of less than 0.5 . In most cases, a tantalum capacitor will
satisfy this requirement.
Figure 6 shows the complete circuit along with its effi-
ciency curve.
LOAD(MAX)
IN
L
L
will require an RMS current rating of at least 0.125A
LTC3405A-1.5/LTC3405A-1.8
1 5
f
.
V
OUT
Figure 5. LTC3405A-1.8 Suggested Layout
MHz
/2 at temperature and C
1
I
L
1 8
L1
OUT
.
(
V
100
V
OUT
SW
= 1.8V, V
PIN 1
mA
C
1
OUT
)
1
V
V
OUT
LTC3405A-1.8
IN
IN
1 8
4 2
VIA TO V
GND
= 4.2V, I
.
.
www.DataSheet4U.com
V
V
OUT
IN
will require an ESR
6 8
C
IN
.
sn3405a1518 3405a1518fs
L
= 100mA and
H
11
3405A1518 F05
V
IN
(3)