LTC3649
APPLICATIONS INFORMATION
low ripple causes inductor current sensing issues. High-
est efficiency operation is obtained at low frequency with
reasonably small ripple current. However, achieving this
requires a large inductor. There is a trade-off between
component size, efficiency and operating frequency.
very low. A 10μF ceramic capacitor is usually enough for
these conditions. Place this input capacitor as physically
close to the V pin as possible.
IN
Inductor Selection
Given the desired input and output voltages, the inductor
valueandoperatingfrequencydeterminetheripplecurrent:
A reasonable starting point is to choose a ripple current
that is about 508 of I
. To guarantee that ripple
OUT(MAX)
current does not exceed specified inductor saturation cur-
rentratings,theinductanceshouldbechosenaccordingto:
V
f •L
VOUT
OUT
∆IL =
1−
IN(MAX)
V
VOUT
VOUT
L =
1−
IN(MAX)
Lower ripple current reduces core losses in the inductor
and reduces output voltage ripple. However, at extremes,
f • ∆IL(MAX)
V
Table 1. Inductor Selection Table
INDUCTOR
INDUCTANCE (µH)
DCR (mΩ)
ꢀ.ꢀ9
MAX CURRENT (A)
17.4
14.0
10.9
27.4
25.4
23.6
21.ꢀ
1ꢀ.3
17.5
10.6
ꢀ.4
DIMENSIONS (mm)
ꢀ.6 × ꢀ.1
HEIGHT (mm)
ꢀ.0
MANUFACTURER
XALꢀ0ꢀ0 Series
4.7
6.ꢀ
10.0
3.3
4.7
5.6
6.ꢀ
ꢀ.2
10.0
2.1
3.9
4.9
6.9
2.2
3.3
4.7
5.6
6.ꢀ
10.0
2.4
3.3
4.2
5.5
6.5
7.ꢀ
10.0
Coilcraft
www.coilcraft.com
13.20
21.00
3.70
ꢀ.6 × ꢀ.1
ꢀ.0
ꢀ.6 × ꢀ.1
ꢀ.0
XAL1010 Series
FDV0ꢀ40 Series
11.3 × 10
10.0
10.0
10.0
10.0
10.0
10.0
4.0
5.20
11.3 × 10
6.30
11.3 × 10
ꢀ.10
11.3 × 10
11.70
13.40
10.40
1ꢀ.ꢀ0
24.60
31.70
ꢀ.20
11.3 × 10
11.3 × 10
9.1 × ꢀ.4
Toko
www.toko.com
9.1 × ꢀ.4
4.0
6.9
9.1 × ꢀ.4
4.0
6.1
9.1 × ꢀ.4
4.0
IHLP-4040DZ-A1
Series
25.6
1ꢀ.6
17.0
16.0
13.5
12.0
17.0
15.0
14.0
12.0
10.0
9.5
11.5 × 10.3
11.5 × 10.3
11.5 × 10.3
11.5 × 10.3
11.5 × 10.3
11.5 × 10.3
10.6 × 10.6
10.6 × 10.6
10.6 × 10.6
10.6 × 10.6
10.6 × 10.6
10.6 × 10.6
10.6 × 10.6
4.0
Vishay
www.vishay.com
13.70
15.00
17.60
21.20
33.20
3.50
4.0
4.0
4.0
4.0
4.0
WE-HCI 1050 Series
5.0
Wurth Elektronik
www.we-online.com
5.90
5.0
7.10
5.0
10.30
12.50
13.60
16.30
5.0
5.0
5.0
ꢀ.5
5.0
3649fb
14
For more information www.linear.com/LTC3649
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