MP2611 – 2A, 1-CELL SWITCHING CHARGER FOR USB AND ADAPTER POWER

MP2611 Rev. 1.12

www.MonolithicPower.com

12

12/7/2012

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© 2012 MPS. All Rights Reserved.

OPERATION

The MP2611 is a monolithic switching charger

with built-in power MOSFETs for a single-cell Li-

Ion battery pack. It achieves up to a 2A charge

current that can be programmed through an

accurate sense resistor over the whole input

range. It can operate with separate inputs for

USB and AC adapter: For USB mode, the input

current limit can be programmed to 500mA and

900mA via the USBM-pin for both USB2.0 and

USB3.0.

Charge Cycle (Trickle Charge

CC Charge

CV Charge)

loops to realize highly-accurate constant current

(CC) charge and constant voltage (CV) charge.

The device uses the resistor RS1 to sense the

battery charge current and amplifies the signal

using the internal amplifier A3 (Figure 1). The

charge starts in trickle-charge mode (TC, 10% of

reaches 3V. If the charger stays in the trickle-

charge mode until it triggers a time-out condition,

the charging terminates. Otherwise, the charger

operates in constant-current charging mode. The

COMPI voltage, regulated by the amplifier GMI,

determines the duty cycle.

When the battery voltage rises to the constant-

voltage mode threshold, the amplifier GMV

regulates the COMP-pin and the duty cycle.

Consequently, the charger operates in constant-

voltage mode.

Figure 2: Li-Ion Battery Charge Profile

ACIN and USBIN Detection

There are two separate battery charger inputs;

ACIN for the AC adapter, and USBIN for the USB

port.

ACIN is used as the battery-charger primary

power supply. As soon as the ACIN voltage

exceeds ACIN UVLO (3.75V), Q1 turns on and

Q2 turns off. The adapter charges the battery

with up to 2A constant charge current through the

step-down DC/DC converter implemented by Q1

and Q3. The charge current can be set by RS1.

If the ACIN input is absent or less than 3.75V, the

USBIN can act as the power supply for the

battery charger: Q1 turns off and Q2 turns on.

USB supply mode uses the input current limit

loop so that the threshold can be programmed by

AGND.

When ACIN and USBIN are both absent, Q1 and

Q2 are completely off and the reverse blocking

function blocks the battery reverse-leakage

current to the input port.

Note that if ACIN and USBIN are both present,

the device selects the AC adapter as the power

supply of the charger. However, avoid this

practice.

DC/DC Converter

The MP2611 integrates both the high-side switch

and the synchronous low-side switch, which

provides high efficiency and eliminates the

external Schottky diode.

During normal operation, the high-side switch

turns on for a period of time to ramp-up the

inductor current at each rising edge of the

internal oscillator, and switches off when the

peak inductor current rises above the COMP

voltage. Once the high-side switch turns off, the

synchronous switch turns on immediately and

stays on until the next cycle starts (see Figure 1).

The device allows the high-side switch to remain

on for more than one switching cycle and

increases the duty cycle while the input voltage

drops close to the output voltage. When the duty

cycle reaches 100%, the high-side switch is held

on continuously to deliver current to the output.