LT3579EFE-1 データシートの表示（PDF） - Linear Technology

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LT3579EFE-1

6A Boost/Inverting DC/DC Converter with Fault Protection

Linear Technology 

LT3579/LT3579-1

APPENDIX

Table 5. Inductor Manufacturers

Vishay

IHLP-2020BZ-01 and

IHLP-2525CZ-01 Series

Coilcraft

XLP, MLC and MSS Series

Cooper Bussmann DRQ125 and DRQ127

Series

Sumida

CDRH series

TDK

RLF and SLF series

Würth

WE-PD, WE-PDF, WE-HC

and WE-DD Series

www.vishay.com

www.coilcraft.com

www.cooperbussmann.

com

www.sumida.com

www.tdk.com

www.we-online.com

Minimum Inductance

Although there can be a tradeoff 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) 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:

( ) LBOOST

>

DC • VIN − VCESAT

2• fOSC

•

⎛

⎝⎜IPK

−

VOUT •IOUT

VIN • η

⎞

⎠⎟

Boost

Topology

or

( ) SEPIC

LDUAL

>

2

•

fOSC

DC •

⎛

• ⎝⎜IPK

VIN − VCESAT

− |VOUT |•IOUT

VIN • η

⎞

− IOUT ⎠⎟

or

Inverting

Topologies

where:

LBOOST = L1 for Boost Topologies (see Figure 6)

LDUAL = L1 = L2 for Coupled Dual Inductor

Topologies (see Figures 7 and 8)

LDUAL = L1 || L2 for Uncoupled Dual Inductor

Topologies (see Figures 7 and 8)

DC = Switch Duty Cycle (see Power Switch Duty

Cycle section in Appendix)

IPK = Maximum Peak Switch Current; Should

Not Exceed 6A for a Combined SW1 +

SW2 Current or 3.4A of SW1 Current (see

Electrical Characteristics section.)

η = Power Conversion Efficiency (typically 90%

for Boost and 85% for Dual Inductor

Topologies at high currents)

fOSC = Switching Frequency

IOUT = Maximum Output Current

Negative values of LBOOST or LDUAL indicate that the

output load current, IOUT, exceeds the switch current limit

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:

( ) ( ( ) ) LMIN =

VIN − VCESAT • 2 • DC − 1

4A • fOSC • 1−DC

where:

LMIN = L1 for Boost Topologies (see Figure 6)

LMIN = L1 = L2 for Coupled Dual Inductor

Topologies (see Figures 7 and 8)

LMIN = L1 || L2 for Uncoupled Dual Inductor

Topologies (see Figures 7 and 8)

35791f

25

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