LTC1473IGN datasheet(9/16 Pages) LINER

9 / 16 page

LTC1473

APPLICATIONS INFORMATION

block current flow in either direction when both switches

are turned off.

The back-to-back topology also allows for independent

control of each half of the switch pair which facilitates

bidirectional inrush current limiting and the so-called

“2-diode mode” described in the following section.

The 2-Diode Mode

Under normal operating conditions, both halves of each

switch pair are turned on and off simultaneously. For

example, when the input power source is switched from

BAT1 to BAT2 in Figure 4, both gates of switch pair SW

A1/B1 are normally turned off and both gates of switch pair

SW A2/B2 are turned on. The back-to-back body diodes in

switch pair, SW A1/B1, block current flow in or out of the

BAT1 input connector.

In the “2-diode mode,” only the first half of each power

path switch pair, i.e., SW A1 and SW A2, are turned on; and

the second half, i.e., SW B1 and SW B2 are turned off.

These two switch pairs now act simply as two diodes

connected to the two main input power sources as illus-

trated in Figure 4. The power path diode with the highest

input voltage passes current through to the output load

(i.e. input of the DC/DC converter) to ensure that the power

management

µP is powered even under start-up or abnor-

mal operating conditions. (An undervoltage lockout circuit

defeats this mode when the V + pin drops below approxi-

mately 3.2V. The supply to V + comes from the main power

sources, DCIN, BAT1 and BAT2 through three external

diodes as shown in Figure 1.)

The 2-diode mode is asserted by applying an active low to

the DIODE input.

COMPONENT SELECTION

N-Channel Switches

The LTC1473 adaptive inrush current limiting circuitry

permits the use of a wide range of logic-level N-Channel

MOSFET switches. A number of dual, low RDS(ON)

N-channel switches in 8-lead surface mount packages are

available that are well suited for LTC1473 applications.

The maximum allowable drain-source voltage, VDS(MAX),

of the two switch pairs, SW A1/B1 and SW A2/B2 must be

high enough to withstand the maximum DC supply volt-

age. If the DC supply is in the 20V to 28V range, use 30V

MOSFET switches. If the DC supply is in the 10V to 18V

range, and is well regulated, then 20V MOSFET switches

will suffice.

Figure 4. LTC1473 PowerPath Switches in 2-Diode Mode

BAT1

DCIN

BAT2

SW A2

SW B2

OFF

RSENSE

HIGH

EFFICIENCY

DC/DC

SWITCHING

REGULATOR

3.3V

1473 F04

12V

POWER

MANAGEMENT

µP

CIN

SW A1

SW B1

OFF

LTC1473

OUTPUT LOAD

LTC1473IGN Datasheet(PDF) 9 Page - Linear Technology

LTC1473IGN Datasheet(HTML) 9 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Datasheet Descarga

Enlace URL