MP2617 – SINGLE CELL SWITCHING CHARGER WITH POWER PATH CONTROL

MP2617 Rev. 1.03

www.MonolithicPower.com

25

8/23/2013

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© 2013 MPS. All Rights Reserved.

APPLICATION INFORMATION

COMPONENT SELECTION

Setting the Input Current Limit

Connect a resistor from the ILIM pin to AGND

to program the input current limit for different

input ports. The relationship between the input

current limit and setting resistor is as following:

IN

ILIM

40000

I1.14

(mA)

R(k )

=×

Ω

(1)

is not over 3A.

For USB input, the input current limit is set by

the M0 and M1 logic, the setting resistor by

ILIM pin is invalid.

Setting the Charge Current

between the charge current and setting resistor

is as following:

CHG

SET

1800

I1.15

(mA)

R(k )

=×

Ω

(2)

Usually in USB mode, the charge current is

always set over the USB input limit specification.

Then the MP2617 regulates the input current

constant at the limitation value. Thus the real

CC charge current is not the setting value, it

varies with different input and battery voltages.

The maximum CC charge value can be

calculated as:

)

A

(

V

I

V

I

TC

ILIM

IN

MAX

_

CC

η

×

×

=

(3)

is the current charge efficiency. Assume

Figure 7 shows a calculating charge current

curve by limiting the input current limit.

1A

2A

3A

3V

4.2V

Battery Voltage

I

IN_

LIM

=2A

I

I

Current Limit

Setting the Input Voltage Limit

The input clamp voltage is set using a resistive

voltage divider from the input voltage to VLIM

pin. The voltage divider divides the input

voltage down to the limit voltage by the ratio:

(V)

R2

+

R1

R2

×

V

=

V

IN_LIM

VLIM

(4)

Thus the input voltage is:

(V)

R2

R2

+

R1

×

V

=

V

VLIM

IN_LIM

(5)

1.52V, and a typical value for R2 can be 10kΩ.

With this value, R1 can be determined by:

(V)

V

V

-

V

×

R2

=

R1

VLIM

VLIM

IN_LIM

(6)

For example, for a 4.65V input limit voltage, R2

is 10kΩ, and R1 is 20.6kΩ.

Setting the System Voltage

The system voltage can be regulated to any

value between 3.6V to 4.4V by the resistor

divider on SYSFB pin as R6 and R7 in Figure 9.

7

R

7

R

6

R

V

V

REF

_

SYS

SYS

+

×

=

(7)

of SYS. With a typical value for R7, 10kΩ, R6

can be determined by: