MP26101 – 2A, 24V INPUT, 1.1MHz 1- OR 2- CELL SWITCHING LI-ION BATTERY CHARGER

MP26101 Rev. 1.01

www.MonolithicPower.com

13

8/4/2020

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APPLICATION INFORMATION

Setting the Charge Current

The sense resistor RS1 sets the charge current

as per the following equation:

)

RS1(m

200mV

(A)

I

CHG





(1)

Table2—ICHG Setting

ICHG(A)

RS(mΩ)

2

100

1.5

133

1

200

0.8

250

0.5

400

Selecting the Inductor

Select an inductor with a typical value between

1µH and 10µH using the following equation.

OUT

IN

OUT

IN

L

OSC

V(V

V

)

L

VI

f





 

(2)

Where ∆IL is the inductor ripple current. VOUT is

the battery voltage.

Choose

an

inductor

current

equal

to

approximately 30% of the maximum charge

current, 2A. The maximum inductor peak current

is:

L

L(MAX)

LOAD

I

II

2





(3)

Under light load conditions below 100mA, use a

larger inductance to improve efficiency. For most

applications, chose an inductor with a DC

resistance less than 200mΩ.

NTC Function

As Figure 5 shows, the low temperature threshold

and high temperature threshold are preset

internally through a resistive divider set at

73.5%·VREF33 and 29.5%·VREF33. For a given

NTC thermistor, we can select an appropriate R3

and an appropriate R6 to set the NTC window.

For example, using the NCP18XH103 thermistor,

At 0°C, RNTC_Cold = 27.445k;

At 50°C, RNTC_Hot = 4.1601k.

Assuming that the NTC window is between 0°C

and 50°C, and given the following equations:

NTC _ Cold

TH _ Low

NTC _ Cold

R6 // R

V

73.5%

R3 R6 // R

VREF33





(4)

TH _ High

NTC _ Hot

NTC _ Hot

V

R6 // R

29.5%

R3 R6 // R

VREF33





(5)

R3 = 9.63k and R6 = 505k. Simplifying, select

R3=10k and leave R6 open to satisfy the

specifications.

NTC

VREF33

Low Temp Threshold

High Temp Threshold

RNTC

R3

R6

VTH_Low

VTH_High

Figure 5— NTC function block

Selecting the Input Capacitor

The input capacitor reduces the surge current

drawn from the input and the switching noise from

the device. Choose an input capacitor with a

switching frequency impedance less than the

input source impedance to prevent high-frequency

switching current from flowing to the input. Use

ceramic capacitors with X5R or X7R dielectrics

with low ESR and small temperature coefficients.

For most applications, use a 4.7µF capacitor.

Selecting the Output Capacitor

The output capacitor limits the output voltage

ripple and ensures regulator loop stability. The

output capacitor impedance should be low at the

switching frequency. Use ceramic capacitors with

X5R or X7R dielectrics.

PC Board Layout

Route the high frequency and high current paths

(GND, IN and SW) to the device using short,

direct, and wide traces. Place the input capacitor