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

MP2612 Rev. 1.0

www.MonolithicPower.com

18

9/7/2011

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© 2011 MPS. All Rights Reserved.

APPLICATION INFORMATION

Setting the Charge Current

1. Standalone Switching Charger

The charge current of MP2612 is set by the

sense resistor RS1 (Figure1). The charge current

programmable formula is as following:





mΩ

RS1

200mV

A

I

CHG



(1)

2.

Switching

Charger

with

Power

Path

Management

When MP2612 is applied together with MP8110,

the charge current setting should be calibrated

(Figure2).

Figure 8 shows MP8110 sensing the system

current and feeding back to the MP2612.

Figure 8— System Current Sensing Circuit

The gain of MP8110 is set as:

RG1

RGS1

Gain



(2)

from:

RG1

RGS1

RS2

I

Gain

RS2

I

V

SYS

SYS

OUT1













(3)

accordingly, the relationship should be:

RG1

RS1

RGS1

RS2

ΔI

RS1

ΔV

ΔI

SYS

OUT1

BAT











(4)

RG1

RGS1

RS2

RS1

(5)

changes the sense gain of A2, which can be

calculated from:







kΩ

RGS

kΩ

2

kΩ

12.3

G

A2





(6)

The charge current is set as:





mΩ

RS1

G

1230

A

I

A2

CHG





(7)

is:







mΩ

RS1

10

Ω

RGS

2000

A

I

CHG







(8)

To decrease the power loss of the sensing circuit,

choose RS2 as small as possible, 20m is

current sense error of MP8110, 50Ω is at least.

Substitute these two values into equation (5),

then the calibrated charge current set formula in

power path application is got from equation (8):







mΩ

RS1

10

mΩ

RS1

2.5

2000

A

I

CHG









(9)

value for setting different charge current.

RS1(mΩ)

2

280

110

1.5

402

160

1

665

260

0.8

909

360

0.5

2k

800

from equation (5) and equation (8), then get the

different equation (9) and the table.