9

LTC4414

4414fc

GND

CTL

SENSE

GATE

STAT

7

3

2

6

8

1

LTC4414

BATTERY

CHARGER

P-CHANNEL

MOSFET

TO LOAD

STATUS OUTPUT

IS LOW WHEN A

WALL ADAPTER

IS PRESENT

47k

*DRAIN-SOURCE DIODE OF MOSFET

4414 F02

BATTERY

CELL(S)

*

WALL

ADAPTER

INPUT

GND

CTL

SENSE

GATE

STAT

7

3

2

6

8

1

LTC4414

PRIMARY

P-CHANNEL

MOSFET

TO LOAD

STATUS OUTPUT

DROPS WHEN A

WALL ADAPTER

IS PRESENT

47k

4414 F01

BATTERY

CELL(S)

WALL

ADAPTER

INPUT

*

*

AUXILIARY

P-CHANNEL

MOSFET

*DRAIN-SOURCE DIODE OF MOSFET

Automatic PowerPath Control

The applications shown in Figures 1 and 2 and the typical

application shown on the first page of this data sheet are

automatic ideal diode controllers that require no assis-

tance from a microcontroller. Each of these will automati-

cally connect the higher supply voltage, after accounting

for certain diode forward voltage drops, to the load with

application of the higher supply voltage. These circuits are

not recommended for load sharing.

The typical application shown on the first page on this data

sheet illustrates an application circuit for automatic

switchover of a load between a battery and a wall adapter

or other power input. With application of the battery, the

load will initially be pulled up by the drain-source diode of

the P-channel MOSFET. As the LTC4414 comes into

action, it will control the MOSFET’s gate to turn it on and

reduce the MOSFET’s voltage drop from a diode drop to

20mV. The system is now in the low loss forward regula-

tion mode. Should the wall adapter input be applied, the

Schottky diode will pull up the SENSE pin, connected to the

load, above the battery voltage and the LTC4414 will turn

the MOSFET off. The STAT pin will then sink current

indicating an auxiliary input is connected. The battery is

now supplying no load current and all the load current

flows through the Schottky diode. A silicon diode could be

used instead of the Schottky, but will result in higher

power dissipation and heating due to the higher forward

voltage drop.

Figure 1 illustrates an application circuit for automatic

switchover of load between a battery and a wall adapter

that features lowest power loss. Operation is similar to the

Typical Application on the front page except that an

auxiliary P-channel MOSFET replaces the diode. The

STAT pin is used to turn on the MOSFET once the SENSE

pin voltage exceeds the battery voltage by 20mV. When

the wall adapter input is applied, the drain-source diode of

the auxiliary MOSFET will turn on first to pull up the

SENSE pin and turn off the primary MOSFET followed by

turning on of the auxiliary MOSFET. Once the auxiliary

MOSFET has turned on the voltage drop across it can be

very low depending on the MOSFET’s characteristics.

Figure 2 illustrates an application circuit for the automatic

switchover of a load between a battery and a wall adapter

in the comparator mode. It also shows how a battery

charger can be connected. This circuit differs from Figure

1 in the way the SENSE pin is connected. The SENSE pin

is connected directly to the auxiliary power input and not

the load. This change forces the LTC4414’s control cir-

cuitry to operate in an open-loop comparator mode. While

the battery supplies the system, the GATE pin voltage will

be forced to its lowest clamped potential, instead of being

regulated to maintain a 20mV drop across the MOSFET.

This has the advantages of minimizing power loss in the

ence of a linear control loop’s dynamics. A possible

disadvantage is if the auxiliary input ramps up slow

enough the load voltage will initially droop before rising.

TYPICAL APPLICATIO S

Figure 1. Automatic Switchover of Load Between a Battery and a

Wall Adapter with Auxiliary P-Channel MOSFET for Lowest Loss

Figure 2. Automatic Switchover of Load Between

a Battery and a Wall Adapter in Comparator Mode