10

LTC4412HV

sn4412hv 4412hvfs

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

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 stays connected. When the primary power is

long enough for the MOSFET to turn on. At a minimum,

transistion between the sets of MOSFETs is complete.

Sufficient capacitance on the load and low or no capaci-

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.

GND

CTL

SENSE

GATE

STAT

1

2

3

6

5

4

LTC4412HV

TO LOAD

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

STATUS IS HIGH

WHEN BAT2 IS

SUPPLYING

LOAD CURRENT

470k

4412HV F05

BAT1

WALL

ADAPTER

INPUT

GND

CTL

SENSE

GATE

STAT

1

2

3

6

5

4

LTC4412HV

470k

BAT2

*

*

*DRAIN-SOURCE DIODE OF MOSFET

Figure 5. Dual Battery Load Sharing with Automatic

Switchover of Load from Batteries to Wall Adapter

GND

CTL

SENSE

GATE

STAT

1

2

3

6

5

4

LTC4412HV

*DRAIN-SOURCE DIODE OF MOSFET

PRIMARY

P-CHANNEL MOSFETS

TO LOAD

4412HV F04

AUXILIARY POWER

SOURCE INPUT

*

*

*

*

PRIMARY

POWER

SOURCE INPUT

AUXILIARY

P-CHANNEL MOSFETS

470k

MICROCONTROLLER

0.1

µF

Figure 4. Microcontroller Monitoring and Control

of Two Power Sources