Typical Delay Time vs. Temperature

10130905

Application Information

The adapter interface circuit (AIC) IC provides the control

functions necessary for use in mating a constant voltage

output AC-DC adapter or airline adapter to a notebook com-

puter system or a portable device. It allows optimal battery

charging during computer operation, and allows battery dis-

charge for battery gas gauge calibration. It receives control

signals from the notebook computer, monitors input current

from the adapter, provides adapter voltage status to the

notebook system management microcontroller (or

″embed-

ded controller

″), and appropriately drives MOSFET switches

to electrically connect the adapter to the computer.

AIC will allow a system designer to solve various power

management tasks typical for an adapter powered systems

containing a rechargeable battery.

When a notebook computer is being powered from a battery

and the adapter is plugged in, the computer should start

drawing power from the adapter, not from the battery. The

most time efficient charging scenario is when a computer

draws the full rated current from a constant voltage adapter.

The computer uses what it needs to run, and passes all

remaining power on to the battery for charging. The com-

puter should be able to automatically refuse to charge a

battery when powered from an airplane power line. It may be

necessary sometimes to have a computer fully discharging

the battery and then fully recharging it (for battery gas gauge

calibration purposes) while being powered by an AC adapter.

AIC will also allow a computer to prevent backfeeding cur-

rent into an adapter if the adapter is not powered while being

plugged into the computer (some of existing adapters can

draw current from the computer under this conditions for

charging the AC adapter output bulk capacitance from the

computer battery).

While the lowest usable adapter voltage is about 9.5V, that is

V

down to V

erate false readings down to V

readings would be MPS = HIGH, ADAPTER PRESENT =

HIGH, CHARGER PRESENT = HIGH.

AIC determines usable voltage ranges by comparing

V

Electrical Characteristics). AIC detects operating current limit

and leakage current limit into the adapter jack by differential

sensing across current sense resistor R

or scaled down by resistor dividers R1/R3 and R2/R4.

When designing the LM2601 into a system it may be neces-

sary to consider ESD protection requirements for the

adapter jack according to your system design spec.

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