Datasheet

LT8582
24
8582f
APPENDIX
use a toroidal or shielded inductor. See Table 5 for a list
of inductor manufacturers.
Table 5. Inductor Manufacturers
Coilcraft MSD7342
XAL6060 Series
www.coilcraft.com
Vishay IHLP-2020BZ-01
IHLP-2525CZ-01
Series
www.vishay.com
WÜRTH WE-PD
WE-DD
WE-TDC Series
www.we-online.com
Cooper Bussman Octa-Pac Plus
DRQ-125
DRQ-74 Series
www.cooperbussmann.com
Sumida CDR6D28MN
CDR7D28MN
Series
www.sumida.com
Taiyo Yuden NR Series www.t-yuden.com
TDK VLF, SLF, RLF
Series
www.tdk.com
Minimum Inductance
Although there can be a trade-off with efficiency, it is
often desirable to minimize board space by choosing
smaller inductors. When choosing an inductor, there are
three conditions that limit the minimum inductance: (1)
providing adequate load current, (2) avoiding subharmonic
oscillation and (3) supplying a minimum ripple current to
avoid false tripping of the current comparator.
Adequate Load Current
Small value inductors result in increased ripple currents
and thus, due to the limited peak switch current, decrease
the average current that can be provided to the load. In
order to provide adequate load current, L should be at least:
L
BOOST
#
DC t (V
IN
– V
CESAT
)
2 t f
OSC
t I
PK
–
V
OUT
t I
OUT
V
IN
t M
©
«
ª
¹
»
º
Boost
Topology
or
L
DUAL
#
DC t (V
IN
–V
CESAT
)
2tf
OSC
t I
PK
–
|V
OUT
|t I
OUT
V
IN
t M
I
OUT
©
«
ª
¹
»
º
SEPIC or
Inverting
Topologies
where
L
BOOST
= L1 for boost topologies (see Figure 5)
L
DUAL
= L1 = L2 for coupled dual inductor topologies
(see Figures 6 and 7)
L
DUAL
= L1 || L2 for uncoupled dual inductor
topologies (see Figures 6 and 7)
DC = Switch duty cycle (see Power Switch Duty
Cycle section in Appendix)
I
PK
= Maximum Peak Switch Current; should not
exceed 3A for a combined SWA + SWB
current, or 1.7A if only SWA is being used.
η = Power conversion efficiency (typically 88%
for boost and 82% for dual inductor
topologies at high currents)
f
OSC
= Switching frequency
I
OUT
= Maximum load current
Negative values of L
BOOST
or L
DUAL
indicate that the
output load current I
OUT
exceeds the switch current limit
capability of the LT8582.
Avoiding Subharmonic Oscillations
Subharmonic oscillations can occur when the duty cycle is
greater than 50%. The LT8582’s internal slope compensa-
tion circuit will avoid this, provided that the inductance
exceeds a certain minimum value. In applications that
operate with duty cycles greater than 50%, the inductance
must be at least:
L
MIN
>
(V
IN
–V
CESAT
)•(2•DC–1)
1.7A • f
OSC
•(1–DC)
where
L
MIN
= L1 for boost topologies (see Figure 5)
L
MIN
= L1 = L2 for coupled dual inductor topologies
(see Figures 6 and 7)
L
MIN
= L1 || L2 for uncoupled dual inductor topologies
(see Figures 6 and 7)