MP2012 – 1.5A SYNCHRONOUS STEP-DOWN CONVERTER

MP2012 Rev. 1.01

www.MonolithicPower.com

8

9/22/2011

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

© 2011 MPS. All Rights Reserved.

APPLICATION INFORMATION

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

Cooper

SD25-3R3

3.3

5.2X5.2X2.5

Toko

D63LCB#A921

CY-3R6M

3.6

6.3X6.2X3

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

(

)

O U T

I N

O U T

O U T

E S R

I N

O S C

O S C

O U T

V

V

V

1

1

V

R

V

f

L

8

f

C

⋅−

⎛⎞

Δ=

+ ⋅

⎜⎟

⋅⋅

⋅

⎝⎠

For most applications, a 22μF capacitor is

sufficient.

Thermal Dissipation

Power dissipation shall be considered when

operates MP2012 at maximum 1.5A output

current. If the junction temperature rises above

150

°C, MP2012 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 MP2012 is operating in a 70

°C

ambient temperature environment:

W

6

.

1

W

/

C

50

C

70

C

150

PD

o

o

o

MAX

=

−

=