MP26057- 28V, 1A LINEAR LI-ION TRAVEL CHARGER WITH TRICKLE CHARGE AND TIMER

MP26057 Rev. 0.91

www.MonolithicPower.com

8

1/25/2010

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© 2010 MPS. All Rights Reserved.

OPERATION

Input Voltage Range

The MP26057 has built-in input voltage surge

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

be automatically enabled when the input voltage

is higher than 3.0 and lower than 7.0V. If the

input voltage is lower than the battery voltage,

the IC is also disabled to prevent the battery from

draining.

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

Figure 2 below shows the typical charging profile

for the MP26057. For a fully depleted battery with

a terminal voltage lower than 2.6V, the MP26057

will start with the trickle charge (preconditioning)

at 10% of the full charge current based on the

mode longer than 32768 cycles, RED/GRN pins

become flashing indicating battery fault. After the

battery voltage reaches 2.6V, the charger begins

charging

at

the

constant

current

of

the

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 current reduced to the preset

terminated. Recharge will start after the battery

voltage is for some reason reduced to 4.0V. After

262144 cycles of continuous charging, if the

battery is still not reaching IBF condition, the on-

chip timer will terminate the charger to prevent

charging the dead battery for excessive long time

and the fault condition will be flagged by flashing

the RED/GRN LEDs.

2.6V

4.2V

Trickle

Charging

CC

Charging

Charging

Complete

CV

Charging

Figure 2—MP26057 Typical Charging Profile

Charge termination

The charge current will gradually decrease in CV

mode as the battery approaches full. The battery

full threshold can be programmed by connecting

a resistor from IBF pin to ground. When the

charge current reaches this threshold, the

charger IC will be automatically turned off. The

battery voltage may decay after termination due

to self discharge or system draw current from the

battery.

Automatic Recharge

automatically restart the charge cycle until the

IBF condition is met again. When the input

adapter is unplugged or the charger is disabled

and/or terminated, the leakage current from the

battery to MP26057 is less than 1µA.

Programming of Charge Current and Battery

Full Current

1.65

1000

1.82

900

2.05

800

2.32

700

2.74

600

3.3

500

4.12

400

5.6

300

8.45

200

15

100

Charge Current vs

1000

900

800

700

600

500

400

300

200

0

0.2

0.1

0.3 0.4

0.6 0.7

0.5

Figure 3—Charge Current vs. 1/RPGM

Resistance