LTC3410-1.875 LINER [Linear Technology], LTC3410-1.875 Datasheet - Page 12

• Manufacturer Part Number: LTC3410-1.875
• Description: 2.25MHz, 300mA Synchronous Step-Down Regulator in SC70
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
LTC3410-1.875
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of the
LTC3410-1.875. These items are also illustrated graphi-
cally in Figures 3 and 4. 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 LTC3410-1.875 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 0.3A but most of the time it will be in
standby mode, requiring only 2mA. Efficiency at both low
12
trace and the V
wide.
possible? This capacitor provides the AC current to the
internal power MOSFETs.
V
OUT
Figure 3. LTC3410-1.875 Layout Diagram
–
+
BOLD LINES INDICATE HIGH CURRENT PATHS
C
IN
OUT
IN
U
trace should be kept short, direct and
will be operating from a maximum of
L1
IN
U
IN
and C
1
2
3
connect to V
RUN
SW
LTC3410-1.875
GND
OUT
5
W
as close as possible.
V
OUT
V
C
IN
IN
IN
6
4
as closely as
34101875 F03
U
V
IN
and high load currents is important. With this informa-
tion we can calculate L using Equation (1),
Substituting V
and f = 2.25MHz in Equation (3) gives:
A 4.7µH inductor works well for this application. For best
efficiency choose a 360mA or greater inductor with less
than 0.3Ω series resistance.
C
I
of less than 0.5Ω. In most cases, a ceramic capacitor will
satisfy this requirement.
Figure 5 shows the complete circuit along with its
efficiency curve.
LOAD(MAX)
IN
L
L
will require an RMS current rating of at least 0.125A ≅
=
=
( )
2 25
f
.
( )
Figure 4. LTC3410-1.875 Suggested Layout
V
1
∆
/2 at temperature and C
OUT
I
MHz
L
SW
1 875
L1
.
OUT
V
OUT
(
100
= 1.875V, V
PIN 1
V
⎛
⎜
⎝
1
C
mA
OUT
−
V
)
V
OUT
⎛
⎝ ⎜
LTC3410-
IN
1
1.875
VIA TO V
−
⎞
⎟
⎠
IN
1 875
.
4 2
OUT
= 4.2V, ∆I
IN
.
C
IN
V
will require an ESR
V
⎞
⎠ ⎟
=
4
L
34101875 F04
.6 6 µH
V
= 100mA
IN
34101875f
3 ( )