MP2615

– 2A, 1- CELL OR 2- CELL LI-ION BATTERY CHARGER

MP2615 Rev. 1.0

www.MonolithicPower.com

17

1/16/2014

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

© 2014 MPS. All Rights Reserved.

APPLICATION INFORMATION

COMPONENT SELECTION

Charge Current Setting

can be set by the sense resistor RS1 (see

Typical Application). The equation to determine

the

programmable

CC-charge

current

is

expressed as following,

CC

100mV

I

(A)

RS1(m )





(4)

be obtained by the following equation,

(A)

)

RS1(m

10mV

10%I

I

CC

TC







(5)

Inductor Selection

To select the right inductor, a trade off should be

made between cost, size, and efficiency. An

inductor of lower inductance value corresponds

with smaller size, but it results in higher ripple

currents, higher magnetic hysteretic losses, and

higher output capacitances. Conversely, higher

inductance value is beneficial to getting a lower

ripple current and smaller output filter capacitors,

but resulting in higher inductor DC resistance

(DCR) loss. Based on practical experience, the

inductor ripple current should not exceed 30% of

the maximum charge current under worst cases.

For the MP2615 with a typical 12V input voltage

to charge a 2-cell battery, the maximum inductor

current ripple occurs at the corner point between

Inductance estimations are as follow:

S

IN

BATT

L_MAX

BATT

IN

f

V

V

ΔI

V

-

V

L





(6)

voltage, the CC charge threshold, and the

switching frequency, respectively. And

L_MAX

ΔI

is

the maximum inductor ripple current, which is

usually 30% of the CC charge current.

CC

L_MAX

30%I

ΔI



(7)

inductance is 6.6µH. The inductor saturation

current must exceed 2.6A at least and have

some tolerance. To optimize efficiency, chose an

inductor with a DC resistance less than 5

0mΩ.

NTC Resistor Divider Selection

Figure shows that an internal resistor divider is

used to set the low temperature threshold and

high temperature threshold at 73.3%·VCC and

29.3%·VCC, respectively. For a given NTC,

the NTC window.

NTC

VCC

Low Temp Threshold

High Temp Threshold

Figure 5: NTC Function Block

The thermistor (NCP18XH103) noted above has

the following electrical characteristic:





The following equations are derived assuming

that the NTC window is between 0°C and 50°C:

73.3%

=

VREF33

V

=

//R

R

+

R

//R

R

TH_Low

NTC_Cold

T2

T1

NTC_Cold

T2

(8)

29.3%

=

VREF33

V

=

//R

R

+

R

//R

R

TH_High

NTC_Hot

T2

T1

NTC_Hot

T2

(9)

According to Equation (8) (9), and the required