MP2149 –6V, 1A, LOW QUIESCENT CURRENT, DUAL, SYNC BUCK REGULATOR

MP2149 Rev.1.01

www.MonolithicPower.com

10

5/31/2013

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

© 2013 MPS. All Rights Reserved.

APPLICATION INFORMATION

COMPONENT SELECTION

Output Voltage

External resistor dividers connected to the FB

pins set the output voltages. The feedback

resistor connected to FB1 (R1) also sets the

50kHz

and

100kHz

for

optimal

transient

performance and good phase margin. When

using an electrolytic capacitor, set the loop

bandwidth no higher than 1/4 the ESR zero

ESR

ESR

O

1

f

2π RC

=

⋅⋅

We suggest using a 600k to 800k resistor for R1

OUT

R1

R2

V

1

0.608V

=

−

Table 1: Resistor Values vs. Output Voltage

R1

R2

L

(Ceramic)

1.2V

806kΩ

825kΩ

0.47μH-2.2μH

22μF

1.5V

806kΩ

549kΩ

0.47μH-2.2μH

22μF

1.8V

806kΩ

412kΩ

0.47μH-2.2μH

22μF

2.5V

806kΩ

261kΩ

1μH-4.7μH

22μF

3.3V

806kΩ

182kΩ

1μH-4.7μH

22μF

Inductor Selection

Use a 1.5µH-to-2.2µH inductor with a DC current

rating of at least 1.25 times the maximum load

current for most applications. For best efficiency,

select an inductor with a DC resistance <20mΩ.

See Table 2 for recommended inductors. For

most designs, estimate the inductance value

using the following equation:

OUT

IN

OUT

IN

L

OSC

V(V

V

)

L

V

ΔIf

−

=

⋅⋅

inductor ripple current equal to approximately

30% of the maximum load current, 1A.

The maximum inductor peak current is:

L

L(MAX)

LOAD

ΔI

I= I

+

2

Table 2: Suggested Surface-Mount Inductors

Vendor

Part

Number

L

(μH)

DCR

(mΩ)

SC

(A)

L x W x H

(mm

WURTH

744777002

2.2

13

6

7.3×7.3×4.5

744310200

2

14.2

6.5

7×6.9×3

TDK

RLF7030T-

1R5N6R1-T

1.5

8

6.5

7.8×6.8×3.2

Input Capacitor

The input capacitor reduces the surge current

drawn from the input and the switching noise

from the device. Select an input capacitor with a

switching-frequency impedance that is less than

the input source impedance to prevent high-

frequency-switching current from passing to the

input source. Use low-ESR ceramic capacitors

with

X5R

or

X7R

dielectrics

with

small

temperature coefficients. For most applications, a

22µF capacitor is sufficient.

Output Capacitor

The output capacitor limits the output voltage

ripple and ensures a stable regulation loop.

Select an output capacitor with low impedance at

the switching frequency. Use ceramic capacitors

with X5R or X7R dielectrics. Using an electrolytic

capacitor may result in additional output voltage

ripple, thermal issues, and requires additional

care in selecting the feedback resistor (R1) due

approximately:

OUT

IN

OUT

OUT

IN

OSC

OSC

O

V(V

V

)

1

ΔVESR

Vf

L

8 f

C

⎛⎞

−

=⋅

+

⎜⎟

⋅⋅

⋅⋅

⎝⎠

Power Dissipation

IC power dissipation plays an important role in

circuit design—not only because of efficiency

concerns, but also because of the chip’s thermal

requirements.

Several

parameters

influence

power dissipation, such as:

• Conduction Loss (Cond)

• Dead Time (DT)