LTC1473 LINER [Linear Technology], LTC1473 Datasheet - Page 9

• Manufacturer Part Number: LTC1473
• Description: Dual PowerPathTM Switch Driver
• Manufacturer: LINER [Linear Technology]

APPLICATIONS
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
BAT1
BAT2
DCIN
U
INFORMATION
U
ON
SW A1
Figure 4. LTC1473 PowerPath Switches in 2-Diode Mode
SW B1
W
OFF
ON
SW A2
LTC1473
U
SW B2
OFF
management P is powered even under start-up or abnor-
mal operating conditions. (An undervoltage lockout circuit
defeats this mode when the V
mately 3.2V. The supply to V
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 R
N-channel switches in 8-lead surface mount packages are
available that are well suited for LTC1473 applications.
The maximum allowable drain-source voltage, V
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.
R
SENSE
+
C
IN
MANAGEMENT
REGULATOR
SWITCHING
EFFICIENCY
POWER
DC/DC
OUTPUT LOAD
HIGH
P
+
comes from the main power
+
pin drops below approxi-
1473 F04
12V
5V
3.3V
LTC1473
DS(MAX)
DS(ON)
9
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