LTC4411
7
4411fa
tion mode, the forward voltage will be kept low by control-
ling the gate voltage of the internal MOSFET to react to
changes in load current. Should the wall adapter input be
applied, the Schottky diode will pull up the output voltage,
connected to the load, above the battery voltage. The
LTC4411 will sense that the output voltage is higher than
the battery voltage and will turn off the internal MOSFET.
The STAT pin will then sink current indicating an auxiliary
input is connected. The battery is now supplying no load
current and all load current flows through the Schottky
diode.
Microcontrolled PowerPath Monitoring and Control
Figure 6 illustrates an application circuit for microcontroller
monitoring and control of two power sources. The
microcontroller’s analog inputs, perhaps with the aid of a
resistor voltage divider, monitors each supply input and
commands the LTC4411 through the CTL input. Back-to-
back MOSFETs are used so that the parasitic drain-source
diode will not power the load when the MOSFET is turned
off (dual MOSFETs in one package are commercially
available).
Figure 5. Automatic Switchover of Load Between a
Primary and an Auxiliary Power Source with External
Dual P-Channel MOSFETs
Figure 6. Dual Battery Load Sharing with Automatic
Switchover of Load from Batteries to Wall Adapter
LOAD
STATUS
IN
GND
CTL
OUT
STAT
LTC4411
1
2
3
5
4
C2
4.7µF
C1
10µF
AUXILIARY P-CHANNEL
MOSFETS
MICROCONTROLLER
PRIMARY
POWER
SOURCE
AUXILIARY
POWER
SOURCE
R1
470k
4411 F05
C1: C0805C106K8PAC
C2: C1206C475K8PAC
WHEN BOTH STATUS LINES ARE
HIGH, THEN BOTH BATTERIES
ARE SUPPLYING LOAD CURRENT.
WHEN BOTH STATUS LINES ARE
LOW, THEN WALL ADAPTER IS
PRESENT AND SUPPLYING FULL
LOAD CURRENT
IN
GND
CTL
OUT
STAT
LTC4411
1
2
3
BAT2
4411 F06
IN
GND
CTL
OUT
STAT
LTC4411
1
2
3
WALL
ADAPTER
INPUT
TO
LOAD
C
OUT
4.7µF
STATUS IS HIGH WHEN
BAT2 IS SUPPLYING
LOAD CURRENT
STATUS IS HIGH WHEN
BAT1 IS SUPPLYING
LOAD CURRENT
BAT1
470k
V
CC
470k
V
CC
5
4
C
IN
1µF
C
IN
1µF
C
IN
: C0805C105K8PAC
C
OUT
: C1206C475K8PAC
turn off and no load current will be drawn from the
batteries. The STAT pins provide information as to which
input is supplying the load current. This concept can be
expanded to more power inputs.
Multiple Battery Charging
Figure 7 illustrates an application circuit for automatic dual
battery charging from a single charger. Whichever battery
has the lower voltage will receive the charging current until
both battery voltages are equal, then both will be charged.
When both are charging simultaneously, the higher ca-
pacity battery will get proportionally higher current from
the charger. For Li-Ion batteries, both batteries will achieve
the float voltage minus the forward regulation voltage of
40mV. This concept can apply to more than two batteries.
The STAT pin provides information as to which batteries
are being charged. For intelligent control, the CTL pin input
can be used with a microcontroller as shown in Figure 5.
Figure 7. Automatic Dual Battery Charging
from a Single Charging Source
IN
GND
CTL
OUT
STAT
LTC4411
1
2
3
4411 F07
IN
GND
CTL
OUT
STAT
LTC4411
1
2
3
BATTERY
CHARGER
INPUT
TO LOAD OR
PowerPath
CONTROLLER
TO LOAD OR
PowerPath
CONTROLLER
STATUS IS HIGH
WHEN BAT2 IS
CHARGING
STATUS IS HIGH
WHEN BAT1 IS
CHARGING
470k
V
CC
470k
V
CC
5
4
BAT1
BAT2
APPLICATIO S I FOR ATIO
WUU
U
Load Sharing
Figure 6 illustrates an application circuit for dual battery
load sharing with automatic switchover of load from
batteries to wall adapter. Whichever battery is capable of
supplying the higher voltage will provide the load current
until it is discharged to the voltage of the other battery. The
load will then be shared between the two batteries accord-
ing to the capacity of each battery. The higher capacity
battery will provide proportionally higher current to the
load. When a wall adapter input is applied, both LTC4411s
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
