LT1375/LT1376
APPLICATIONS INFORMATION
5. After making an initial choice, consider the secondary
things like output voltage ripple, second sourcing, etc.
Use the experts in the Linear Technology’s applica-
tions department if you feel uncertain about the final
choice. They have experience with a wide range of
inductor types and can tell you about the latest devel-
opments in low profile, surface mounting, etc.
Table 2
VENDOR/
PART NO.
Coiltronics
CTX5-1
CTX10-1
CTX20-1
CTX15-2
CTX20-3
CTX20-4
CTX5-1P
CTX10-1P
CTX15-1P
CTX20-1P
CTX20-2P
CTX20-4P
Sumida
CDRH64
CDRH74
CDRH73
CDRH73
CD73
CD73
CD104
CD104
Gowanda
SM20-102K
SM20-152K
SM20-222K
Dale
IHSM-4825
IHSM-4825
IHSM-5832
IHSM-5832
IHSM-7832
10
22
10
22
22
3.1
1.7
4.3
2.8
3.8
Open
Open
Open
Open
Open
0.071
0.152
0.053
0.12
0.054
Fer
Fer
Fer
Fer
Fer
5.6
5.6
7.1
7.1
7.1
10
15
22
1.3
1.3
1.3
Open
Open
Open
0.038
0.049
0.059
Fer
Fer
Fer
7.0
7.0
7.0
10
22
10
22
10
18
10
18
1.7
1.2
1.7
1.1
1.4
1.1
2.4
1.7
SC
SC
SC
SC
Open
Open
Open
Open
0.084
0.077
0.055
0.15
0.062
0.085
0.041
0.062
Fer
Fer
Fer
Fer
Fer
Fer
Fer
Fer
4.5
4.5
3.4
3.4
3.5
3.5
4.0
4.0
5
10
20
15
20
20
5
10
15
20
20
20
2.3
1.9
1.0
1.8
1.5
2.2
1.8
1.6
1.2
1.0
1.3
1.8
Tor
Tor
Tor
Tor
Tor
Tor
Tor
Tor
Tor
Tor
Tor
Tor
0.027
0.039
0.137
0.058
0.093
0.059
0.021
0.030
0.046
0.081
0.052
0.039
KMµ
KMµ
KMµ
KMµ
KMµ
KMµ
52
52
52
52
52
52
4.2
4.2
4.2
6.0
4.7
6.4
4.2
4.2
4.2
4.2
6.0
6.35
VALUE DC
CORE
(
µ
H) (Amps) TYPE
SERIES
RESIS-
TANCE(
Ω
)
CORE
MATER- HEIGHT
IAL
(mm)
Tor = Toroid
SC = Semi-closed geometry
Fer = Ferrite core material
52 = Type 52 powdered iron core material
KMµ = Kool Mµ
12
U
W
U
U
Output Capacitor
The output capacitor is normally chosen by its Effective
Series Resistance (ESR), because this is what determines
output ripple voltage. At 500kHz, any polarized capacitor
is essentially resistive. To get low ESR takes
volume,
so
physically smaller capacitors have high ESR. The ESR
range for typical LT1376 applications is 0.05Ω to 0.5Ω. A
typical output capacitor is an AVX type TPS, 100µF at 10V,
with a guaranteed ESR less than 0.1Ω. This is a “D” size
surface mount solid tantalum capacitor. TPS capacitors
are specially constructed and tested for low ESR, so they
give the lowest ESR for a given volume. The value in
microfarads is not particularly critical, and values from
22µF to greater than 500µF work well, but you cannot
cheat mother nature on ESR. If you find a tiny 22µF solid
tantalum capacitor, it will have high ESR, and output ripple
voltage will be terrible. Table 3 shows some typical solid
tantalum surface mount capacitors.
Table 3. Surface Mount Solid Tantalum Capacitor ESR
and Ripple Current
E Case Size
ESR (Max.,
Ω
)
Ripple Current (A)
AVX TPS, Sprague 593D
AVX TAJ
D Case Size
AVX TPS, Sprague 593D
AVX TAJ
C Case Size
AVX TPS
AVX TAJ
B Case Size
AVX TAJ
2.5 to 10
0.16 to 0.08
0.2 (typ)
1.8 to 3.0
0.5 (typ)
0.22 to 0.17
0.1 to 0.3
0.9 to 2.0
0.7 to 1.1
0.36 to 0.24
0.1 to 0.3
0.7 to 0.9
0.7 to 1.1
0.4
Many engineers have heard that solid tantalum capacitors
are prone to failure if they undergo high surge currents.
This is historically true, and type TPS capacitors are
specially tested for surge capability, but surge ruggedness
is not a critical issue with the
output
capacitor. Solid
tantalum capacitors fail during very high
turn-on
surges,
which do not occur at the output of regulators. High
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