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

MP2611 Rev. 1.12

www.MonolithicPower.com

16

12/7/2012

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

© 2012 MPS. All Rights Reserved.

APPLICATION INFORMATION

Setting the Charge Current in AC Mode

of the MP2611 (see Typical Application). The

equation to determine the programmable CC-

charge is as follows:

(A)

)

RS1(m

100mV

I

CC

Ω

=

(1)

For either AC mode or USB mode, the trickle

charge current is given by the following equation:

(A)

)

RS1(m

10mV

10%I

I

CC

TC

Ω

=

=

(2)

Setting the USB Input Current Limit

In USB supply mode, connect a resistor from the

USBM pin to AGND to program the input current

limit for different USB ports. The relationship

between the input current limit and setting

resistor is as following:

(mA)

)

(k

R

37000

I

ILIM

USB_LIM

Ω

=

(3)

is in the range of 0A to 2A. If using a resistor

smaller than 18.5kΩ, the MP2611 suppresses

Note that in USB mode, the MP2611 doesn’t

monitor the charge current through RS1 during

CC charge phase, but regulates the input current

CC charge current varies with different input and

battery voltages. Figure 5 shows the charge

current

vs.

battery

voltage

curve

when

The maximum CC charge value can be

calculated as:

(A)

V

η

I

V

I

TC

USB_LIM

USBIN

CC_MAX

⋅

⋅

=

(4)

is

the

current

charge

efficiency.

Assume

For certain battery packs, the CC charge current

Selecting the Inductor

Inductor selection trades off between cost, size,

and efficiency. A lower inductance value

corresponds with smaller size, but results in

higher ripple currents, higher magnetic hysteretic

losses, and higher output capacitances. However,

a higher inductance value benefits from lower

ripple current and smaller output filter capacitors,

but results in higher inductor DC resistance (DCR)

loss. From a practical standpoint, the inductor

ripple current does not exceed 15% of the

maximum charge current under worst cases. For

a MP2611 with a typical 5V input voltage, the

maximum inductor current ripple occurs at the

corner point between trickle charge and CC

charge

Estimate

the

required

inductance as:

S

IN

BATT

L_MAX

BATT

IN

f

V

V

ΔI

V

-

V

L

⋅

=

(5)

voltage, the CC charge threshold, and the

switching frequency, respectively.

L_MAX

ΔI

is the

maximum inductor ripple current ,which is usually

15% of the CC charge current.