MP2263

– 30V, 3A, LOW IQ, SYNCHRONOUS, STEP-DOWN CONVERTER

MP2263 Rev. 1.0

www.MonolithicPower.com

14

6/22/2016

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

© 2016 MPS. All Rights Reserved.

APPLICATION INFORMATION

Setting the Output

The external resistor divider is used to set the

output voltage (see the Typical Application on

page 1). Refer to Table 1 to choose R1. R2 can

then be calculated with Equation (3):

OUT

R1

R2

V

1

0.8V





(3)

The feedback network is highly recommended

(see Figure 5).

Figure 5: Feedback Network

Table

1 lists the recommended feedback

network

parameters

for

common

output

voltages.

Table 1: Recommended Parameters for Common

Output Voltages

(7)

1.05

470

1500

5.6

1.2

750

1500

5.6

1.8

1000

806

5.6

2.5

1000

470

5.6

3.3

1000

324

5.6

5

1000

191

5.6

NOTE:

7) The recommended parameters are based on a 500kHz

switching frequency. A different input voltage, output inductor

value, or output capacitor value may affect the selection of

refer to the Typical Application Circuits on pages 16 and 17.

Selecting the Inductor

For most applications, use a 1µH to 22µH

inductor with a DC current rating at least 25%

higher than the maximum load current. For the

highest efficiency, use an inductor with a DC

resistance less than 15mΩ. For most designs,

the inductance value can be derived from

Equation (4):

OUT

IN

OUT

1

IN

L

OSC

V

(V

V

)

L

V

I

f





  

(4)

Where

∆I

Choose the inductor ripple current to be

approximately 30%

of the maximum load

current. The maximum inductor peak current

can be calculated with Equation (5):

2

I

I

I

L

LOAD

)

MAX

(

L







(5)

Selecting the Input Capacitor

The input current to the step-down converter is

discontinuous

and

therefore

requires

a

capacitor

to

supply

AC

current

while

maintaining the DC input voltage. Use low ESR

capacitors for optimum performance. Ceramic

capacitors with X5R or X7R dielectrics are

recommended because of their low ESR and

small

temperature

coefficients.

For

most

applications, use two 10µF capacitors. Since

C1 absorbs the input switching current, it

requires an adequate ripple-current rating. The

RMS current in the input capacitor can be

estimated with Equation (6):

























IN

OUT

IN

OUT

LOAD

1

C

V

V

1

V

V

I

I

(6)

shown in Equation (7):

2

I

I

LOAD

1

C



(7)

For simplification, choose an input capacitor

that has an RMS current rating greater than half

the maximum load current.

The input capacitor can be electrolytic, tantalum,

or ceramic. When using electrolytic or tantalum

capacitors,

a

small,

high-quality,

ceramic

capacitor (e.g.:

0.1μF) should be placed as

close to the IC as possible. When using

ceramic capacitors, ensure that they have

enough capacitance to provide sufficient charge

to prevent excessive voltage ripple at input. The

input voltage ripple caused by capacitance can

be estimated with Equation (8):

LOAD

OUT

OUT

IN

IN

S

IN

I

V

V

V1

f

C1

V

V









 







(8)