Datasheet

12
LT1375/LT1376
13756fd
APPLICATIONS INFORMATION
WUU
U
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
SERIES CORE
VENDOR/ VALUE DC CORE RESIS- MATER- HEIGHT
PART NO. (
µ H) (Amps) TYPE TANCE( Ω ) IAL (mm)
Coiltronics
CTX5-1 5 2.3 Tor 0.027 KMµ 4.2
CTX10-1 10 1.9 Tor 0.039 KMµ 4.2
CTX20-1 20 1.0 Tor 0.137 KMµ 4.2
CTX15-2 15 1.8 Tor 0.058 KMµ 6.0
CTX20-3 20 1.5 Tor 0.093 KMµ 4.7
CTX20-4 20 2.2 Tor 0.059 KMµ 6.4
CTX5-1P 5 1.8 Tor 0.021 52 4.2
CTX10-1P 10 1.6 Tor 0.030 52 4.2
CTX15-1P 15 1.2 Tor 0.046 52 4.2
CTX20-1P 20 1.0 Tor 0.081 52 4.2
CTX20-2P 20 1.3 Tor 0.052 52 6.0
CTX20-4P 20 1.8 Tor 0.039 52 6.35
Sumida
CDRH64 10 1.7 SC 0.084 Fer 4.5
CDRH74 22 1.2 SC 0.077 Fer 4.5
CDRH73 10 1.7 SC 0.055 Fer 3.4
CDRH73 22 1.1 SC 0.15 Fer 3.4
CD73 10 1.4 Open 0.062 Fer 3.5
CD73 18 1.1 Open 0.085 Fer 3.5
CD104 10 2.4 Open 0.041 Fer 4.0
CD104 18 1.7 Open 0.062 Fer 4.0
Gowanda
SM20-102K 10 1.3 Open 0.038 Fer 7.0
SM20-152K 15 1.3 Open 0.049 Fer 7.0
SM20-222K 22 1.3 Open 0.059 Fer 7.0
Dale
IHSM-4825 10 3.1 Open 0.071 Fer 5.6
IHSM-4825 22 1.7 Open 0.152 Fer 5.6
IHSM-5832 10 4.3 Open 0.053 Fer 7.1
IHSM-5832 22 2.8 Open 0.12 Fer 7.1
IHSM-7832 22 3.8 Open 0.054 Fer 7.1
Tor = Toroid
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
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 0.1 to 0.3 0.7 to 1.1
AVX TAJ 0.7 to 0.9 0.4
D Case Size
AVX TPS, Sprague 593D 0.1 to 0.3 0.7 to 1.1
AVX TAJ 0.9 to 2.0 0.36 to 0.24
C Case Size
AVX TPS 0.2 (typ) 0.5 (typ)
AVX TAJ 1.8 to 3.0 0.22 to 0.17
B Case Size
AVX TAJ 2.5 to 10 0.16 to 0.08
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