ltc4414ems8-trpbf Linear Technology Corporation, ltc4414ems8-trpbf Datasheet - Page 9

• Manufacturer Part Number: ltc4414ems8-trpbf
• Description: 36v, Low Loss Powerpath Controller For Large Pfets
• Manufacturer: Linear Technology Corporation

Automatic PowerPath Control
The applications shown in Figures 1 and 2 and the typical
application shown on the first page of this data sheet are
automatic ideal diode controllers that require no assis-
tance from a microcontroller. Each of these will automati-
cally connect the higher supply voltage, after accounting
for certain diode forward voltage drops, to the load with
application of the higher supply voltage. These circuits are
not recommended for load sharing.
The typical application shown on the first page on this data
sheet 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 LTC4414 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 LTC4414 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.
TYPICAL APPLICATIO S
ADAPTER
Figure 1. Automatic Switchover of Load Between a Battery and a
Wall Adapter with Auxiliary P-Channel MOSFET for Lowest Loss
BATTERY
CELL(S)
INPUT
WALL
7
3
2
*DRAIN-SOURCE DIODE OF MOSFET
V
GND
CTL
LTC4414
IN
SENSE
GATE
STAT
6
8
1
P-CHANNEL
P-CHANNEL
AUXILIARY
PRIMARY
MOSFET
MOSFET
*
*
47k
U
4414 F01
C
OUT
TO LOAD
STATUS OUTPUT
DROPS WHEN A
WALL ADAPTER
IS PRESENT
Figure 1 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 the
Typical Application on the front page 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 2 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 LTC4414’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 2. Automatic Switchover of Load Between
a Battery and a Wall Adapter in Comparator Mode
7
3
2
*DRAIN-SOURCE DIODE OF MOSFET
V
GND
CTL
CHARGER
BATTERY
LTC4414
IN
SENSE
GATE
STAT
6
8
1
P-CHANNEL
MOSFET
*
ON
and not having the influ-
V
CC
47k
LTC4414
C
OUT
4414 F02
TO LOAD
STATUS OUTPUT
IS LOW WHEN A
WALL ADAPTER
IS PRESENT
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