Datasheet

11
LT1506
APPLICATIONS INFORMATION
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Table 2
SERIES CORE
VENDOR/ VALUE DC CORE RESIS- MATER- HEIGHT
PART NO. ( µ H) (Amps) TYPE TANCE( Ω ) IAL (mm)
Coiltronics
CTX2-1 2 4.1 Tor 0.011 KMµ 4.2
CTX5-4 5 4.4 Tor 0.019 KMµ 6.4
CTX8-4 8 3.5 Tor 0.020 KMµ 6.4
CTX2-1P 2 3.4 Tor 0.014 52 4.2
CTX2-3P 2 4.6 Tor 0.012 52 4.8
CTX5-4P 5 3.3 Tor 0.027 52 6.4
Sumida
CDRH125 10 4.0 SC 0.025 Fer 6
CDRH125 12 3.5 SC 0.027 Fer 6
CDRH125 15 3.3 SC 0.030 Fer 6
CDRH125 18 3.0 SC 0.034 Fer 6
Coilcraft
DT3316-222 2.2 5 SC 0.035 Fer 5.1
DT3316-332 3.3 5 SC 0.040 Fer 5.1
DT3316-472 4.7 3 SC 0.045 Fer 5.1
Pulse
PE-53650 4 4.8 Tor 0.017 Fer 9.1
PE-53651 5 5.4 Tor 0.018 Fer 9.1
PE-53652 9 5.5 Tor 0.022 Fer 10
PE-53653 16 5.1 Tor 0.032 Fer 10
Dale
IHSM-4825 2.7 5.1 Open 0.034 Fer 5.6
IHSM-4825 4.7 4.0 Open 0.047 Fer 5.6
IHSM-5832 10 4.3 Open 0.053 Fer 7.1
IHSM-5832 15 3.5 Open 0.078 Fer 7.1
IHSM-7832 22 3.8 Open 0.054 Fer 7.1
Tor = Toroid
SC = Semiclosed 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 LT1506 applications is 0.05Ω to 0.2Ω. 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
C Case Size
AVX TPS 0.2 (typ) 0.5 (typ)
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
discharge surges, such as when the regulator output is
dead shorted, do not harm the capacitors.
Unlike the input capacitor, RMS ripple current in the
output capacitor is normally low enough that ripple cur-
rent rating is not an issue. The current waveform is
triangular with a typical value of 200mA
RMS
. The formula
to calculate this is:
Output Capacitor Ripple Current (RMS):
I
VVV
LfV
RIPPLE RMS
OUT IN OUT
IN
( )
=
()
−
()
()()( )
029.