Datasheet
LTC3417
10
3417fd
APPLICATIONS INFORMATION
Inductor Core Selection
Different core materials and shapes will change the size/cur-
rent relationship of an inductor. Toroid or shielded pot cores
in ferrite or permalloy materials are small and don’t radiate
much energy, but generally cost more than powdered iron
core inductors with similar electrical characteristics. The
choice of which style inductor to use often depends more
on the price vs size requirements of any radiated fi eld/EMI
requirements than on what the LTC3417 requires to oper-
ate. Table 1 shows some typical surface mount inductors
that work well in LTC3417 applications.
Input Capacitor (C
IN
) Selection
In continuous mode, the input current of the converter can
be approximated by the sum of two square waves with
duty cycles of approximately V
OUT1
/V
IN
and V
OUT2
/V
IN
. To
prevent large voltage transients, a low equivalent series
resistance (ESR) input capacitor sized for the maximum
RMS current must be used. Some capacitors have a
de-rating spec for maximum RMS current. If the capaci-
tor being used has this requirement, it is necessary to
calculate the maximum RMS current. The RMS current
calculation is different if the part is used in “in phase” or
“out of phase”.
For “in phase”, there are two different equations:
V
OUT1
> V
OUT2
:
I
RMS
= 2•I
1
•I
2
•D2(1–D1)+ I
2
2
(D2 – D2
2
)+ I
1
2
(D1– D1
2
)
V
OUT2
> V
OUT1
:
I
RMS
= 2•I
1
•I
2
•D1(1–D2)+ I
2
2
(D2 – D2
2
)+ I
1
2
(D1– D1
2
)
where:
D1=
V
OUT1
V
IN
and D2 =
V
OUT2
V
IN
Table 1
MANUFACTURER PART NUMBER VALUE (μH) MAX DC CURRENT (A) DCR DIMENSIONS L × W × H (mm)
L1 on OUT1
Toko A920CY-1R5M-D62CB 1.5 2.8 0.014 6 × 6 × 2.5
A918CY-1R5M-D62LCB 1.5 2.9 0.018 6 × 6 × 2
Coilcraft DO1608C-152ML 1.5 2.6 0.06 6.6 × 4.5 × 2.9
Sumida CDRH4D22/HP 1R5 1.5 3.9 0.031 5 × 5 × 2.4
CDRH2D18/HP 1R7 1.7 1.8 0.035 3.2 × 3.2 × 2
Midcom DUP-1813-1R4R 1.4 5.5 0.033 4.3 × 4.8 × 3.5
L2 on OUT2
Toko A915AY-2R0M-D53LC 2.0 3.9 0.027 5 × 5 × 3
Coilcraft DO1608C-222ML 2.2 2.3 0.07 6.6 × 4.5 × 2.9
Sumida CDRH3D16/HP 2R2 2.2 1.75 0.047 4 × 4 × 1.8
CDRH2D18/HP 2R2 2.2 1.6 0.035 3.2 × 3.2 × 2
Midcom DUP-1813-2R2R 2.2 3.9 0.047 4.3 × 4.8 × 3.5