LTC3616 LINER [Linear Technology], LTC3616 Datasheet - Page 15

• Manufacturer Part Number: LTC3616
• Description: 6A, 4MHz Monolithic Synchronous Step-Down DC/DC Converter
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
Ferrite designs have very low core losses and are preferred
at high switching frequencies, so design goals can con-
centrate on copper loss and preventing saturation. Ferrite
core material saturates “hard,” meaning that inductance
collapses abruptly when the peak design current is ex-
ceeded. This results in an abrupt increase in inductor
ripple current and consequently output voltage ripple. Do
not allow a ferrite core to saturate!
Different core materials and shapes will change the size/cur-
rent and price/current 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
characteristics. The choice of which style inductor to use
mainly depends on the price versus size requirements
and any radiated field/EMI requirements. Table 1 shows
some typical surface mount inductors that work well in
LTC3616 applications.
Input Capacitor (C
In continuous mode, the source current of the top P-chan-
nel MOSFET is a square wave of duty cycle V
prevent large voltage transients, a low ESR capacitor sized
for the maximum RMS current must be used at V
The maximum RMS capacitor current is given by:
This formula has a maximum at V
I
for design because even significant deviations do not offer
much relief. Note that ripple current ratings from capacitor
manufacturers are often based on only 2000 hours of life
which makes it advisable to further derate the capacitor,
or choose a capacitor rated at a higher temperature than
required. Several capacitors may also be paralleled to meet
size or height requirements in the design.
OUT
I
RMS
/2. This simple worst-case condition is commonly used
=I
OUT(MAX)
IN
•
) Selection
V
V
OUT
IN
•
⎛
⎝ ⎜
IN
V
V
OUT
= 2V
IN
– 1
OUT
⎞
⎠ ⎟
, where I
OUT
/V
IN
RMS
IN
.
. To
=
Table 1. Representative Surface Mount Inductors
Vishay IHLP-2525CZ-01
Sumida CDMC6D28 Series
Cooper HCP0703 Series
Wurth Electronik WE-HC744312 Series
Coilcraft SLC7530 Series
INDUCTANCE
0.100
0.188
0.272
0.350
0.400
(μH)
0.10
0.15
0.20
0.22
0.33
0.47
0.47
0.22
0.47
0.68
0.25
0.47
0.2
0.3
0.123
0.100
0.100
0.100
0.100
(mΩ)
DCR
1.5
1.9
2.4
2.5
3.5
2.5
3.2
4.2
2.8
4.2
5.5
2.5
3.4
4
CURRENT (A)
MAX
21.7
15.4
13.6
60
52
41
40
30
26
23
17
15
18
16
20
21
14
11
8
DIMENSIONS
7.25 × 4.4
7.25 × 4.4
7.25 × 4.4
6.5 × 6.9
6.5 × 6.9
6.5 × 6.9
6.5 × 6.9
6.5 × 6.9
6.5 × 6.9
7.5 × 6.7
7.5 × 6.7
7.5 × 6.7
7.5 × 6.7
7.5 × 6.7
7 × 7.3
7 × 7.3
7 × 7.3
7 × 7.7
7 × 7.7
(mm)
LTC3616
HEIGHT
15
(mm)
3.0
3.0
3.0
3.8
3.8
3
3
3
3
3
3
3
3
3
3
3
3
3
3
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