MP2608- 28V, 1A DUAL INPUT LINEAR BATTERY CHARGER WITH TIMER

MP2608 Rev. 0.9

www.MonolithicPower.com

9

8/29/2008

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© 2008 MPS. All Rights Reserved.

OPERATION

Input Auto Selection and Voltage Range

The MP2608 is a dual-input charger, when both

input sources are present, MP2608 selects only

one power source to charge the battery. When

the adapter input voltage is higher than the

UVLO threshold, IN is selected as the power

source. Otherwise the USB input is selected. If

both the inputs is above UVLO but the adaptor

input voltage is below the battery voltage, while

the USB voltage is higher than the battery

voltage, then the USB input is used to charge the

battery.

In case there is no power source available or

both the two input are below the UVLO, the

MP2608 is in the sleep mode, in which the

current into the BATT pin is reduced to TBD µA.

The IC is also disabled to prevent the battery

from draining.

The MP2608 has built-in input voltage surge

protection as high as +28V. The charger IC will

be automatically disabled when the input voltage

is lower than 2.5V or higher than 6.0V.

Charge Cycle (Mode Change: Trickle -> CC-> CV)

Figure 2 below shows the typical charging profile

for the MP2608. For a fully depleted battery with

a terminal voltage lower than 2.6V, the MP2608

will start with the trickle charge (preconditioning)

at 10% of the programmed full charge current.

After the battery voltage reaches 2.6V, the

charger begins charging at the constant current

timer starts counting down. This is referred to as

Constant Current (CC) mode. Once the battery

voltage reaches 4.2V, the charger will operate in

the constant voltage (CV) mode until the battery

is fully charged. The charge current drops during

CV mode, and the battery full indication is set

when the charge timer is time off. The charge

timer is to protect the system from charging a

dead battery for excessive long time.

POWER DISSIPATION

Timer

Charge

End

CV

Mode

CC

Mode

Trickle

Charging

Charge

Start

Figure 2—MP2608 Typical Charging Profile

Charge Termination and Auto-Recharge

trimmed charge target, the MP2608 reduces its

charge current to 0µA. This ensures the safety of the

battery. Also, the CV control loop always monitors the

battery voltage such that it will automatically recharge

the battery when it is depleted below the target level.

automatically restart the charge cycle until the end of

the timeout. When the input adapter is unplugged,

there is only 1µA leakage current from battery drawn

by the MP2608.

Programming of Charge Current and Battery

Full Current

be programmed from 0.1A to 1A by a resistor

The relationship of the charge current and the

programming resistance is established by the

following table and graph.

The recommended resistance for programming

the charge current is TBD.The battery full charge

current

threshold

programmed

by

When the USB is selected as the power source, the

charge current is fixed at a pre-set value 450mA,

which is a typical value of USB current.