LTC4412HV_15 Datasheet, PDF (10/12 Pages) Linear Technology – 36V, Low Loss PowerPath Controller in ThinSOT

LTC4412HV
TYPICAL APPLICATIO S
rising. This is due to the SENSE pin voltage rising above
the battery voltage and turning off the MOSFET before the
Schottky diode turns on. The factors that determine the
magnitude of the voltage droop are the auxiliary input rise
time, the type of diode used, the value of C_OUT and the load
current.
Ideal Diode Control with a Microcontroller
Figure 4 illustrates an application circuit for microcontrol-
ler 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 LTC4412HV through the CTL input. Back-
to-back MOSFETs are used so that the drain-source diode
will not power the load when the MOSFET is turned off (dual
MOSFETs in one package are commercially available).
With a logical low input on the CTL pin, the primary input
supplies power to the load regardless of the auxiliary
voltage. When CTL is switched high, the auxiliary input
will power the load whether or not it is higher or lower
than the primary power voltage. Once the auxiliary is on,
the primary power can be removed and the auxiliary will
continue to power the load. Only when the primary
voltage is higher than the auxiliary voltage will taking CTL
low switch back to the primary power, otherwise the
AUXILIARY POWER
SOURCE INPUT
AUXILIARY
P-CHANNEL MOSFETS
*
*
470k
MICROCONTROLLER
PRIMARY
P-CHANNEL MOSFETS
*
*
0.1µF
PRIMARY
POWER
SOURCE INPUT
1 ^LTC4412HV 6
V_IN SENSE
2
5
GND GATE
3
4
CTL STAT
*DRAIN-SOURCE DIODE OF MOSFET
4412HV F04
TO LOAD
C_OUT
auxiliary stays connected. When the primary power is
disconnected and V_IN falls below V_LOAD, it will turn on the
auxiliary MOSFET if CTL is low, but V_LOAD must stay up
long enough for the MOSFET to turn on. At a minimum,
C_OUT capacitance must be sized to hold up V_LOAD until the
transistion between the sets of MOSFETs is complete.
Sufficient capacitance on the load and low or no capaci-
tance on V_IN will help ensure this. If desired, this can be
avoided by use of a capacitor on V_IN to ensure that V_IN
falls more slowly than V_LOAD.
Load Sharing
Figure 5 illustrates an application circuit for dual battery
load sharing with automatic switchover of load from
batteries to wall adapter. Whichever battery can supply 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 according 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 MOSFETs will turn off
and no load current will be drawn from the batteries. The
STAT pins provide information as to which input is supply-
ing the load current. This concept can be expanded to
more power inputs.
WALL
ADAPTER
INPUT
BAT1
BAT2
*
1 ^LTC4412HV 6
V_IN SENSE
2
5
GND GATE
3
4
CTL STAT
*
TO LOAD
C_OUT
V_CC
470k
STATUS IS HIGH
WHEN BAT1 IS
SUPPLYING
LOAD CURRENT
WHEN BOTH STATUS LINES ARE
HIGH, THEN BOTH BATTERIES ARE
SUPPLYING LOAD CURRENTS. WHEN
BOTH STATUS LINES ARE LOW THEN
WALL ADAPTER IS PRESENT
1 ^LTC4412HV 6
V_IN SENSE
2
5
GND GATE
3
4
CTL STAT
V_CC
470k
4412HV F05
*DRAIN-SOURCE DIODE OF MOSFET
STATUS IS HIGH
WHEN BAT2 IS
SUPPLYING
LOAD CURRENT
Figure 4. Microcontroller Monitoring and Control
of Two Power Sources
10
Figure 5. Dual Battery Load Sharing with Automatic
Switchover of Load from Batteries to Wall Adapter
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