MP26075 – HIGH EFFICIENCY CRADLE CHARGER

MP26075 Rev. 1.01

www.MonolithicPower.com

8

5/23/2011

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© 2011 MPS. All Rights Reserved.

OPERATION

The high-efficiency linear charger is mainly for

plug-in, cradle charger applications. The device

features using a photo-coupler to directly

feedback the charge voltage and charge current

information

to

the

primary

side.

It

is

recommended to use with flyback controller for

smooth system setup.

Figure 2 is the typical configuration for the

charger with photo-coupler feedback to control

the AC adapter. The voltage change of the CTL

pin will be transferred to the comp pin of the AC

adapter controller by the photo-coupler, which

controls the conduction time of the primary side

switch. The output voltage at secondary side of

the transformer is then adjusted.

EMI

Filter+

Rectifier

Fly-back

Controller

VIN

GND

CTL

COM

TMR

ISET

LED-R

LED-G

BATT

NTC

MP26075

AC

Input

Single Cell

Battery

Photo-Coupler

COMP

Figure 2— System Configuration

Input Voltage Range

The MP26075 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 2.2V or higher than 6.3V. If the

input voltage is lower than the battery voltage,

the IC is also disabled to prevent the battery from

draining. The MP26075 includes a proprietary

input reverse polarity circuit that eliminates the

requirement for an external Schottky diode.

Charge Cycle (Mode Change: Precharge->

Trickle -> CC-> CV)

Figure 3 below shows the typical charge profile

for the MP26075. For a fully depleted battery with

a terminal voltage lower than 2.1V, the MP26075

will start with 1mA pre-charge. If the charger

stays in the pre-charge mode longer than 512

indicate the battery fault, and the charge is

terminated. And when battery voltage reaches

2.1V the MP26075 will start the trickle charge

(preconditioning) at 10% of the full charge current

in the trickle mode longer than 16384 cycles,

LED-R and LED-G

pins become high to indicate

battery fault, and the charge is terminated. After

the battery voltage reaches 3.0V, the charger

begins charge at the constant current of the

the constant current (CC) mode. Once the

battery voltage reaches the battery regulation

voltage (e.g.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 10% of the

the charge process is terminated. Recharge will

start after the battery voltage is reduced to 8% of