Datasheet
LTC4415
13
4415fa
Typical applicaTions
Precision enable inputs and independent status outputs
provide flexibility in power supply back up and load share
applications using the two high current ideal diode circuits
in the LTC4415, as shown in the following examples. The
features shown in these application circuits can be com-
bined in custom applications as needed.
Prioritized Switchover to a Backup Battery
The application circuit, Figure 5, illustrates switchover
from a primary power source to backup power at a pre-
cise input voltage using the prioritized power supply-OR
application circuit. Diode 2 is enabled when the primary
power source voltage on diode 1 input falls below the
threshold given as follows:
V
IN1
<0.8V • 1+
R1+R2
R3
As V
IN1
falls further, diode 1 is disabled when the primary
power source voltage falls below the threshold determined
by the resistor divider on enable pin EN1:
V
IN1
< 0.8V – V
ENHYST
( )
• 1+
R1
R2+R3
The built-in hysteresis on the enable pins in the LTC4415
provides some overlap of diode enables around the swi-
tchover of power supplies. Resistor R2 can be optionally
used for additional overlap between the two supplies. The
additional overlap is given by:
V
OVERLAP
≈ V
ENTH
•
R2
R3
when
R2
R3
<<1
The enable overlap minimizes the load voltage droop during
switchover. Both input power supplies provide power to
the load during the overlap. The status output pins can be
pulled up to the output voltage or to a logic power supply.
Automatic Switchover to a Backup Battery and Keep-
Alive Power Source
Figure 6 illustrates an application circuit for automatic
switchover to the backup battery if the primary power
source voltage falls below the backup battery voltage. The
wired-AND of the status outputs is used to drive the gate
of a pair of back-to-back connected external NMOS (M1
and M2) when both primary and backup power sources
are absent or below UVLO or during thermal shutdown of
LTC4415. Under these conditions, the keep-alive source
supplies power to critical components of the system. At
the same time, the wired-AND status output turns off
Figure 5. Prioritized Power Supply ORing
Figure 6. Automatic Switchover to a Backup Battery with Provision
for Keep-Alive Power to the Load When Both Are Absent
IDEAL
IDEAL
LTC4415
GND
EN1
R1
47k
4415 F06
47µF
LOAD
DMN2215UDM
M1
M2
M3
OPTIONAL
KEEP ALIVE/
COIN CELL
CLIM1
CLIM2
STAT1
WARN1
WARN2
STAT2
EN2
IN2
BACKUP
BAT
IN1 OUT1
OUT2
PRIMARY
POWER
SOURCE
+
IDEAL
IDEAL
LTC4415
GND
EN1
4415 F05
4.7µF
TO
LOAD
R1
R2
R3
R
CLIM2
470k
R
CLIM1
CLIM1
CLIM2
STAT1
WARN1
WARN2
STAT2
EN2
IN2
IN1 OUT1
OUT2
PRIMARY
POWER
SOURCE
SECONDAY
POWER
SOURCE
(BAT)
+
470k
470k
470k