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LTC4085EDE-3-TRPBF

USB Power Manager with Ideal Diode Controller and 3.95V Li-Ion Charger

Linear Technology 

LTC4085-3/LTC4085-4

OPERATION

The LTC4085 is a complete PowerPath controller for bat-

tery powered USB applications. The LTC4085 is designed

to receive power from a USB source, a wall adapter, or a

battery. It can then deliver power to an application con-

nected to the OUT pin and a battery connected to the

BAT pin (assuming that an external supply other than the

battery is present). Power supplies that have limited cur-

rent resources (such as USB VBUS supplies) should be

connected to the IN pin which has a programmable current

limit. Battery charge current will be adjusted to ensure that

the sum of the charge current and load current does not

exceed the programmed input current limit.

An ideal diode function provides power from the battery

when output/load current exceeds the input current limit or

when input power is removed. Powering the load through

the ideal diode instead of connecting the load directly to

the battery allows a fully charged battery to remain fully

charged until external power is removed. Once external

power is removed the output drops until the ideal diode is

forward biased. The forward biased ideal diode will then

provide the output power to the load from the battery.

Furthermore, powering switching regulator loads from the

OUT pin (rather than directly from the battery) results in

shorter battery charge times. This is due to the fact that

switching regulators typically require constant input power.

When this power is drawn from the OUT pin voltage (rather

than the lower BAT pin voltage) the current consumed

by the switching regulator is lower leaving more current

available to charge the battery.

The LTC4085 also has the ability to receive power from

a wall adapter. Wall adapter power can be connected to

the output (load side) of the LTC4085 through an exter-

nal device such as a power Schottky or FET, as shown in

Figure 1. The LTC4085 has the unique ability to use the

output, which is powered by the wall adapter, as a path

to charge the battery while providing power to the load. A

wall adapter comparator on the LTC4085 can be configured

to detect the presence of the wall adapter and shut off the

connection to the USB to prevent reverse conduction out

to the USB bus.

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