LTC3417_15 Datasheet, PDF (10/20 Pages) Linear Technology – Dual Synchronous 1.4A/800mA 4MHz Step-Down DC/DC Regulator

LTC3417
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 field/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 •I₁ •I₂ • D2(1– D1) + I₂₂(D2 – D2²) + I₁₂(D1– D1²)
V_OUT2 > V_OUT1:
I_RMS = 2 •I₁ •I₂ • D1(1– D2) + I₂₂(D2 – D2²) + I₁₂(D1– D1²)
where:
D1=
V_OUT1
V_IN
and
D2
=
V_OUT2
V_IN
Table 1
MANUFACTURER
L1 on OUT1
Toko
Coilcraft
Sumida
Midcom
L2 on OUT2
Toko
Coilcraft
Sumida
Midcom
PART NUMBER
A920CY-1R5M-D62CB
A918CY-1R5M-D62LCB
DO1608C-152ML
CDRH4D22/HP 1R5
CDRH2D18/HP 1R7
DUP-1813-1R4R
A915AY-2R0M-D53LC
DO1608C-222ML
CDRH3D16/HP 2R2
CDRH2D18/HP 2R2
DUP-1813-2R2R
VALUE (μH) MAX DC CURRENT (A)
DCR DIMENSIONS L × W × H (mm)
1.5
2.8
0.014 6 × 6 × 2.5
1.5
2.9
0.018 6 × 6 × 2
1.5
2.6
0.06 6.6 × 4.5 × 2.9
1.5
3.9
0.031 5 × 5 × 2.4
1.7
1.8
0.035 3.2 × 3.2 × 2
1.4
5.5
0.033 4.3 × 4.8 × 3.5
2.0
3.9
0.027 5 × 5 × 3
2.2
2.3
0.07 6.6 × 4.5 × 2.9
2.2
1.75
0.047 4 × 4 × 1.8
2.2
1.6
0.035 3.2 × 3.2 × 2
2.2
3.9
0.047 4.3 × 4.8 × 3.5
3417fd
10