MP2612 – 2A, 24V INPUT, 600kHz 2-3CELL SWITCHING LI-ION BATTERY CHARGER

MP2612 Rev. 1.0

www.MonolithicPower.com

12

9/7/2011

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© 2011 MPS. All Rights Reserved.

OPERATION

The MP2612 is a peak current mode controlled

switching charger for use with Li-Ion batteries.

Figure 3 shows the block diagram. At the

beginning of a cycle, M1 is off. The COMP

voltage is higher than the current sense result

from amplifier A1’s output and the PWM

comparator’s output is low. The rising edge of the

600 kHz CLK signal sets the RS Flip-Flop. Its

output turns on M1 thus connecting the SW pin

and inductor to the input supply.

The increasing inductor current is sensed and

amplified by the Current Sense Amplifier A1.

Ramp compensation is summed to the output of

A1 and compared to COMP by the PWM

comparator.

When the sum of A1’s output and the Slope

Compensation

signal

exceeds

the

COMP

voltage, the RS Flip-Flop is reset and M1 is

turned off. The external switching diode D2 then

conducts the inductor current.

If the sum of A1’s output and the Slope

Compensation signal does not exceed the COMP

voltage, then the falling edge of the CLK resets

the Flip-Flop.

The MP2612 have two internal linear regulators

power internal circuit, VREF33 and VREF25. The

output of 3.3V reference voltage can also power

external circuitry as long as the maximum current

(50mA) is not exceeded. A 1μF bypass capacitor

is required from VREF33 to GND to ensure

stability. The output of 2.5V reference voltage

can not carry any load.

In typical application, VREF25 should be float

and no capacitor is required. It can only connect

to a capacitor which is smaller than 100pF.

Charge Cycle (Mode change: Trickle CC

CV)

The battery current is sensed via RS1 (Figure 3)

and amplified by A2. The charge will start in

reaches 2.8V/cell. If the charge stays in the

“trickle charging mode” till “timer out” condition is

triggered, the charge is terminated. Otherwise,

the output of A2 is then regulated to the level set

current charging mode.” The duty cycle of the

switcher is determined by the COMPI voltage

that is regulated by the amplifier GMI.

When the battery voltage reaches the “constant

voltage mode” threshold, the amplifier GMV will

regulate the COMP pin, and then the duty cycle.

The charger will then operate in “constant voltage

mode.”

Automatic Recharge

A programmable time delay after the battery

charging current drops below the termination

threshold, the charger will cease charging and

some reason, the battery voltage is lowered to

4.0V/Cell, recharge will automatically kick in.

0.1uF

C

1min

Delay

n

Terminatio

TMR





Charger Status Indication

MP2612 has two open-drain status outputs:

CHGOK

and ACOK . The ACOK pin pulls low

when an input voltage is greater than battery

voltage 300mV and over the under voltage

status of the charge cycle. Table 1 describes the

status of the charge cycle based on the

CHGOK

and ACOK outputs.

Table 1―Charging Status Indication

ACOK

CHGOK

Charger status

low

low

In charging

low

high

End of charge,

high

high

Vin<UVLO, timer out,

thermal shutdown

EN

disable

Timer Operation

MP2612 uses internal timer to terminate the

charge if the timer times out. The timer duration

is programmed by an external capacitor at the

TMR pin.

The trickle mode charge time is: