LTC4412IS6#PBF Linear Technology, LTC4412IS6#PBF Datasheet - Page 9

• Manufacturer Part Number: LTC4412IS6#PBF
• Description: LEAD FREE LOW LOSS POWERPATH CONTROLLER
• Manufacturer: Linear Technology

Specifications of LTC4412IS6#PBF

• Rohs Compliant: YES
• Leaded Process Compatible: Yes
• Peak Reflow Compatible (260 C): Yes

Automatic PowerPath Control
The applications shown in Figures 1, 2 and 3 are automatic
ideal diode controllers that require no assistance from a
microcontroller. Each of these will automatically connect
the higher supply voltage, after accounting for certain
diode forward voltage drops, to the load with application
of the higher supply voltage.
Figure 1 illustrates an application circuit for automatic
switchover of a load between a battery and a wall adapter
or other power input. With application of the battery, the
load will initially be pulled up by the drain-source diode of
the P-channel MOSFET. As the LTC4412 comes into
action, it will control the MOSFET’s gate to turn it on and
reduce the MOSFET’s voltage drop from a diode drop to
20mV. The system is now in the low loss forward regula-
tion mode. Should the wall adapter input be applied, the
Schottky diode will pull up the SENSE pin, connected to the
load, above the battery voltage and the LTC4412 will turn
the MOSFET off. The STAT pin will then sink current
indicating an auxiliary input is connected. The battery is
now supplying no load current and all the load current
flows through the Schottky diode. A silicon diode could be
used instead of the Schottky, but will result in higher
power dissipation and heating due to the higher forward
voltage drop.
ADAPTER
TYPICAL APPLICATIO S
Figure 2. Automatic Switchover of Load Between a Battery and a
Wall Adapter with Auxiliary P-Channel MOSFET for Lowest Loss
BATTERY
CELL(S)
INPUT
WALL
1
2
3
*DRAIN-SOURCE DIODE OF MOSFET
V
GND
CTL
LTC4412
IN
SENSE
GATE
STAT
6
5
4
P-CHANNEL
P-CHANNEL
AUXILIARY
PRIMARY
MOSFET
MOSFET
*
*
470k
U
4412 F02
C
OUT
TO LOAD
STATUS OUTPUT
DROPS WHEN A
WALL ADAPTER
IS PRESENT
Figure 2 illustrates an application circuit for automatic
switchover of load between a battery and a wall adapter
that features lowest power loss. Operation is similar to
Figure 1 except that an auxiliary P-channel MOSFET
replaces the diode. The STAT pin is used to turn on the
MOSFET once the SENSE pin voltage exceeds the battery
voltage by 20mV. When the wall adapter input is applied,
the drain-source diode of the auxiliary MOSFET will turn
on first to pull up the SENSE pin and turn off the primary
MOSFET followed by turning on of the auxiliary MOSFET.
Once the auxiliary MOSFET has turned on the voltage drop
across it can be very low depending on the MOSFET’s
characteristics.
Figure 3 illustrates an application circuit for the automatic
switchover of a load between a battery and a wall adapter
in the comparator mode. It also shows how a battery
charger can be connected. This circuit differs from Figure
1 in the way the SENSE pin is connected. The SENSE pin
is connected directly to the auxiliary power input and not
the load. This change forces the LTC4412’s control cir-
cuitry to operate in an open-loop comparator mode. While
the battery supplies the system, the GATE pin voltage will
be forced to its lowest clamped potential, instead of being
regulated to maintain a 20mV drop across the MOSFET.
This has the advantages of minimizing power loss in the
MOSFET by minimizing its R
ence of a linear control loop’s dynamics. A possible
disadvantage is if the auxiliary input ramps up slow
enough the load voltage will initially droop before rising.
ADAPTER
BATTERY
CELL(S)
INPUT
WALL
Figure 3. Automatic Switchover of Load Between
a Battery and a Wall Adapter in Comparator Mode
1
2
3
*DRAIN-SOURCE DIODE OF MOSFET
V
GND
CTL
CHARGER
BATTERY
LTC4412
IN
SENSE
GATE
STAT
6
5
4
P-CHANNEL
MOSFET
*
ON
and not having the influ-
V
CC
470k
LTC4412
C
OUT
4412 F03
TO LOAD
STATUS OUTPUT
IS LOW WHEN A
WALL ADAPTER
IS PRESENT
4412fa
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