LT1375/ LT1376
U
W U U
APPLICATIONS INFORMATION
Tor = Toroid
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.
SC = Semi-closed geometry
Fer = Ferrite core material
52 = Type 52 powdered iron core material
KMµ = Kool Mµ
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
tantalumcapacitor, itwillhavehighESR, andoutputripple
voltage will be terrible. Table 3 shows some typical solid
tantalum surface mount capacitors.
Table 2
SERIES
RESIS-
CORE
MATER- HEIGHT
IAL
VENDOR/
PART NO.
VALUE DC
CORE
(µ
H) (Amps) TYPE TANCE(
Ω
)
(mm)
Coiltronics
CTX5-1
5
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
KMµ
KMµ
KMµ
KMµ
KMµ
KMµ
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
CTX10-1
CTX20-1
CTX15-2
CTX20-3
CTX20-4
CTX5-1P
CTX10-1P
CTX15-1P
CTX20-1P
CTX20-2P
CTX20-4P
Sumida
10
20
15
20
20
5
0.039
0.137
0.058
0.093
0.059
0.021
0.030
0.046
0.081
0.052
0.039
10
15
20
20
20
52
52
52
52
Table 3. Surface Mount Solid Tantalum Capacitor ESR
and Ripple Current
52
E Case Size
AVX TPS, Sprague 593D
AVX TAJ
ESR (Max.,
Ω
)
Ripple Current (A)
0.7 to 1.1
0.4
0.1 to 0.3
0.7 to 0.9
CDRH64
CDRH74
CDRH73
CDRH73
CD73
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
0.084
0.077
0.055
0.15
Fer
Fer
Fer
Fer
Fer
Fer
Fer
Fer
4.5
4.5
3.4
3.4
3.5
3.5
4.0
4.0
D Case Size
AVX TPS, Sprague 593D
AVX TAJ
SC
0.1 to 0.3
0.9 to 2.0
0.7 to 1.1
SC
0.36 to 0.24
Open
Open
Open
Open
0.062
0.085
0.041
0.062
C Case Size
AVX TPS
CD73
0.2 (typ)
0.5 (typ)
CD104
AVX TAJ
1.8 to 3.0
0.22 to 0.17
CD104
B Case Size
AVX TAJ
Gowanda
SM20-102K
SM20-152K
SM20-222K
Dale
2.5 to 10
0.16 to 0.08
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
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
speciallytestedforsurgecapability,butsurgeruggedness
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
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
Fer
Fer
Fer
Fer
Fer
5.6
5.6
7.1
7.1
7.1
0.054
12
Linear [ Linear ]
