Datasheet

10
LTC4414
4414fc
V
IN
GND
CTL
SENSE
GATE
STAT
7
3
2
6
8
1
LTC4414
C
OUT
TO LOAD
STATUS
WHEN BOTH STATUS LINES ARE
HIGH, THEN BOTH POWER SUPPLIES
ARE SUPPLYING LOAD CURRENTS.
STATUS
Q1
Q2
47k
4414 F04
V
CC
POWER
SUPPLY1
V
IN
GND
CTL
SENSE
GATE
STAT
7
3
2
6
8
1
LTC4414
47k
V
CC
POWER
SUPPLY2
*
*
*DRAIN-SOURCE DIODE OF MOSFET
Q1, Q2: SUB75P03-07
V
IN
GND
CTL
SENSE
GATE
STAT
7
3
2
6
8
1
LTC4414
*DRAIN-SOURCE DIODE OF MOSFET
PRIMARY
P-CHANNEL MOSFETS
C
OUT
TO LOAD
4414 F03
AUXILIARY POWER
SOURCE INPUT
*
*
*
*
PRIMARY
POWER
SOURCE INPUT
AUXILIARY
P-CHANNEL MOSFETS
470k
OPTIONAL
ZENER
CLAMP
IF V
GS(MAX)
AN ISSUE
MICROCONTROLLER
0.1µF
R
LIMIT
TYPICAL APPLICATIO S
U
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 3 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 LTC4414 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 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
transition 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
. This circuit is not recom-
mended for load sharing.
High Current Power Supply Load Sharing
Figure 4 illustrates an application circuit for dual identical
power supply load sharing. The load will then be shared
between the two power supplies according to their source
impedances. The STAT pins provide information as to
which input is supplying the load current. This concept can
be expanded to more power inputs.
Figure 4. High Current Dual Power Supply Load SharingFigure 3. Microcontroller Monitoring and Control
of Two Power Sources