lt3579iufd-trpbf Linear Technology Corporation, lt3579iufd-trpbf Datasheet - Page 25

• Manufacturer Part Number: lt3579iufd-trpbf
• Description: Lt3579/lt3579-1 6a Boost/inverting Dc/dc Converter With Fault Protection Features
• Manufacturer: Linear Technology Corporation

APPENDIX
Table 5. Inductor Manufacturers
Vishay
Coilcraft
Cooper Bussmann DRQ125 and DRQ127
Sumida
TDK
Würth
Minimum Inductance
Although there can be a tradeoff with effi ciency, 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) avoidance of 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
L
BOOST
DUAL
>
>
2
•
2
f
•
OSC
f
OSC
DC
IHLP-2020BZ-01 and
IHLP-2525CZ-01 Series
XLP , MLC and MSS Series
Series
CDRH series
RLF and SLF series
WE-PD, WE-PDF , WE-HC
and WE-DD Series
•
DC
⎛
⎜
⎝
•
I
•
PK
•
⎛ ⎛
⎜
⎝
(
I
V
or
(
PK
−
V
IN
IN
|
V
−
−
OUT
−
V
V
V
IN
V
CESAT
OUT
V
CESAT
|• •
•
IN
I
OUT
η
•
•
I
)
OUT
η
)
−
www.vishay.com
www.coilcraft.com
www.cooperbussmann.
com
www.sumida.com
www.tdk.com
www.we-online.com
I
⎞
⎟
⎠
OUT
Boost
Topology
⎞
⎟
⎠
SEPIC
or
Inverting
Topologies
where:
Negative values of L
output load current, I
capability of the LT3579.
Avoiding Sub-Harmonic Oscillations
The LT3579’s internal slope compensation circuit will
prevent sub-harmonic oscillations that can occur when
the duty cycle is greater than 50%, provided that the
inductance exceeds a minimum value. In applications that
operate with duty cycles greater than 50%, the inductance
must be at least:
where:
L
L
L
DC
I
η
f
I
L
L
L
L
PK
OSC
OUT
BOOST
DUAL
DUAL
MIN
MIN
MIN
MIN
=
(
= L1 for Boost Topologies (see Figure 6)
= L1 = L2 for Coupled Dual Inductor
= L1 || L2 for Uncoupled Dual Inductor
= Switch Duty Cycle (see Power Switch Duty
= Maximum Peak Switch Current; Should
= Power Conversion Effi ciency (typically 90%
= Switching Frequency
= Maximum Output Current
= L1 for Boost Topologies (see Figure 6)
= L1 = L2 for Coupled Dual Inductor
= L1 || L2 for Uncoupled Dual Inductor
V
IN
Topologies (see Figures 7 and 8)
Topologies (see Figures 7 and 8)
Cycle section in Appendix)
Not Exceed 6A for a Combined SW1 +
SW2 Current or 3.4A of SW1 Current (see
Electrical Characteristics section.)
for Boost and 85% for Dual Inductor
Topologies at high currents)
Topologies (see Figures 7 and 8)
Topologies (see Figures 7 and 8)
−
4
A f
V
CESAT
•
OSC
OUT
BOOST
LT3579/LT3579-1
, exceeds the switch current limit
)
• −
•
(
1
(
2
or L
DC
•
DC
)
DUAL
−
1
)
indicate that the
25
35791f