LTC3403EDD View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
LTC3403EDD Datasheet PDF : 16 Pages
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LTC3403
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
LTC3403. These items are also illustrated graphically in
Figures 6 and 7. Check the following in your layout:
1. The power traces, consisting of the GND trace, the SW
trace and the VIN trace should be kept short, direct and
wide.
2. Does the (+) plate of CIN connect to VIN as closely as
possible? This capacitor provides the AC drive to the
internal power MOSFETs.
3. Keep the (–) plates of CIN and COUT as close as possible.
Design Example
As a design example, assume the LTC3403 is used in a
single lithium-ion battery-powered cellular phone applica-
tion. The VIN will be operating from a maximum of 4.2V
down to about 2.7V. The load current requirement is a
TO DAC
RREF
VIA TO REF
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
(2)
Substituting VOUT = 2.5V, VIN = 4.2V, IL = 240mA and
f = 1.5MHz in Equation (2) 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 ≅
LOAD(MAX)/2 at temperature and COUT will require an
ESR of less than 0.25Ω. In most cases, a ceramic capaci-
tor will satisfy this requirement.
COUT
CIN
GDR 1
VIN 2
GND 3
SW 4
LTC3403
8 VOUT
7 REF
6 MODE CREF
5 RUN
L1
VIA TO GND
VIA TO VIN
3403 F07
Figure 7. Suggested Layout
VIN
2.7V
TO 5V CIN†
10µF
CER
10k
DAC
1000pF
2 LTC3403 4
VIN
SW
6
1
MODE GDR
5
RUN
7
REF
8
VOUT
2.2µH*
VOUT
COUT**
4.7µF
CER
GND
* MURATA LQH32CN2R2M11
3
**
†
TAIYO
TAIYO
YUDEN
YUDEN
JMK212BJ475MG
JMK212BJ106MN
LTC3403 F08
Figure 8
3403f
14
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