LT3580EMS8E-TRPBF(RevC) Ver la hoja de datos (PDF) - Linear Technology

Número de pieza

componentes Descripción

Fabricante

LT3580EMS8E-TRPBF
(Rev.:RevC)

Boost/Inverting DC/DC Converter with 2A Switch, Soft-Start, and Synchronization

Linear Technology 

LT3580

APPLICATIONS INFORMATION

for boost, coupled inductor SEPIC and coupled inductor

inverting topologies, or:

L1 L2 >

DC • VIN



2(f) ILIM

VOUT • IOUT

VIN • 



IOUT 

for the uncoupled inductor SEPIC and uncoupled inductor

inverting topologies.

where:

DC = switch duty cycle (see previous section)

ILIM = switch current limit, typically about 2.4A at 50%

duty cycle (see the Typical Performance Characteristics

section).

η = power conversion efficiency (typically 88% for

boost and 75% for dual inductor topologies at high

currents).

f = switching frequency

Negative values of LMIN1 indicate that the output load

current IOUT exceeds the switch current limit capability

of the LT3580.

Avoiding Subharmonic Oscillations: The LT3580’s internal

slope compensation circuit will prevent subharmonic oscil-

lations 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:

L > VIN • (2 • DC – 1)

(1
DC) • (f) • 0.8

for boost, coupled inductor SEPIC, and coupled inductor

inverting topologies, or:

L1 L2 > VIN • (2 • DC – 1)

(1
DC) • (f) • 0.8

for the uncoupled inductor SEPIC and uncoupled inductor

inverting topologies.

Maximum Inductance: Excessive inductance can reduce

current ripple to levels that are difficult for the current com-

parator (A3 in the Block Diagram) to cleanly discriminate,

thus causing duty cycle jitter and/or poor regulation. The

maximum inductance can be calculated by:

LMAX

=

VIN – VCESAT

IMIN
RIPPLE

•

DC

f

where LMAX is L1||L2 for dual inductor topologies and a

good choice for IMIN-RIPPLE is 300mA.

Current Rating: Finally, the inductor(s) must have a rating

greater than its peak operating current to prevent inductor

saturation resulting in efficiency loss. In steady state, the

peak input inductor current (continuous conduction mode

only) is given by:

IL1
PEAK =

VOUT •IOUT

VIN • 

+ VIN • DC

2 • L1• f

for the boost, uncoupled inductor SEPIC and uncoupled

inductor inverting topologies, or:

IL1
PEAK



|

VOUT •IOUT |

VIN •  • DC

+

VIN • DC

2 • L1• f

for the coupled inductor SEPIC and coupled inductor

inverting topology.

For dual inductor topologies, the peak output inductor

current is given by:

( ) IL2
PEAK

= IOUT

+

VOUT • 1– DC

2 •L2 • f

for the uncoupled inductor topologies, or

IL2
PEAK



IOUT

1– DC

+

VOUT • (1– DC)

2 •L2 • f

for the coupled inductor topologies

Capacitor Selection

Low ESR (equivalent series resistance) capacitors should

be used at the output to minimize the output ripple voltage.

Multilayer ceramic capacitors are an excellent choice, as

they have an extremely low ESR and are available in very

small packages. X5R or X7R dielectrics are preferred, as

these materials retain their capacitance over wider voltage

3580fc

10

Share Link: