MP2125 – DUAL 1.5A, 1.2MHZ SYNCHRONOUS STEP-DOWN CONVERTER

MP2125 Rev. 1.0

www.MonolithicPower.com

8

12/24/2013

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APPLICATION INFORMATION

The MP2125 has two channels: channel 1 and

channel 2. The following formulates are used for

components selection of both channels.

Output Voltage Setting

The external resistor divider sets the output

voltage.

1

O U T

2

R

V

0 . 8

1

R

⎛⎞

=× +

⎜⎟

⎝⎠

Rt is recommended when output voltage is high,

as the Figure 2 shows.

R1

FB

Rt

R2

Figure 2―Feedback Network

Table 1 lists the recommended resistor value for

common output voltages.

Table 1—Resistor Selection vs. Output

Voltage Setting

V

Rt/

kΩ

R1/

kΩ

R2/

kΩ

L1/

μH

C2/

μF

1.2

300

4.99

10

2.2

22

1.8V

243

4.99

4.02

3.3

22

2.5V

100

121

57.6

3.3

22

3.3V

100

121

39

3.3

22

Inductor Selection

A 1μH to 10μH inductor with DC current rating at

least 25% higher than the maximum load current

is recommended for most applications. For best

efficiency, the inductor DC resistance shall be

<200mΩ. See Table 2 for recommended

inductors and manufacturers. For most designs,

the inductance value can be derived from the

following equation:

()

OSC

L

IN

OUT

IN

OUT

f

I

V

V

V

V

L

×

Δ

×

−

×

=

inductor ripple current approximately 30% of the

maximum load current, 1.5A.

The maximum inductor peak current is:

2

I

I

I

L

LOAD

)

MAX

(

L

Δ

+

=

Table 2—Suggested Inductors

Manufacturer

Part

Number

Inductance

(μH)

Dimensions

LxWxH

(mm

Toko

D63CB#A916

CY-3R3M

3.3

6.3X6.2X3.5

Cooper

SD25-3R3

3.3

5.2X5.2X2.5

TDK

SLF7045T-

3R3M2R5-PF

3.3

7X7X4.5

The input capacitor reduces the surge current

drawn from the input and switching noise from

the device. Ceramic capacitors with X5R or X7R

dielectrics are highly recommended because of

their low ESR and small temperature coefficients.

For most applications, a 10μF capacitor is

sufficient.

The output capacitor keeps output voltage ripple

small and ensures regulation loop stable. The

output capacitor impedance shall be low at the

switching frequency. Ceramic capacitors with

X5R or X7R dielectrics are recommended. For

forced PWM mode operation, the output ripple

OUT

IN

OUT

OUT

ESR

IN

OSC

OSC

OUT

V(V

V

)

11

V(R

)

Vf

L

8 f

C

⋅

−

Δ=

+ ⋅

⋅⋅

⋅

For most applications, a 22μF capacitor is

sufficient.

Thermal Dissipation

Power dissipation shall be considered when

operates MP2125 at maximum 1.5A output

current. If the junction temperature rises above

150

°C, MP2125 will be shut down by internal

thermal protection circuitry.

The junction-to-ambient thermal resistance of the

maximum allowable power dissipation is about

1.6W when MP2125 is operating in a 70

°C

ambient temperature environment:

W

6

.

1

W

/

C

50

C

70

C

150

PD

o

o

o

MAX

=

−

=