LTC4411

7

4411f

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

4.7

µF

C1

10

µF

AUXILIARY P-CHANNEL

MOSFETS

MICROCONTROLLER

PRIMARY

POWER

SOURCE

AUXILIARY

POWER

SOURCE

R1

470k

4411 F06

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 F07

IN

GND

CTL

OUT

STAT

LTC4411

1

2

3

WALL

ADAPTER

INPUT

TO

LOAD

4.7

µF

STATUS IS HIGH WHEN

BAT2 IS SUPPLYING

LOAD CURRENT

STATUS IS HIGH WHEN

BAT1 IS SUPPYLING

LOAD CURRENT

BAT1

470k

470k

5

4

C

IN

1

µF

C

IN

1

µF

C

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 F08

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

470k

5

4

BAT1

BAT2

APPLICATIO S I FOR ATIO

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 LTC4411’s

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.