MP2269 - 30V, 1A, LOW IQ, SYNCHRONOUS STEP-DOWN CONVERTER

MP2269 Rev. 1.0

www.MonolithicPower.com

14

10/11/2016

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APPLICATION INFORMATION

Setting the Output

The external resistor divider is used to set the

output voltage (see Typical Application on page

1). Choose R1 by referring to Table 1. 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

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

NOTES:

7) The recommended parameters are based on a 500kHz

switching frequency. A different input voltage, output inductor

value, and output capacitor value may affect the selection of

refer to the Typical Application Circuits on pages 17 and 18.

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

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

Choose

the

inductor

ripple

current

at

approximately 30%

of the maximum

load

current. The maximum inductor peak current is

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 the best performance. Ceramic

capacitors with X5R or X7R dielectrics are

recommended because of their low ESR and

small

temperature

coefficients.

For

most

applications, use one 10µF capacitor.

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

with an RMS current rating greater than half of

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 a sufficient

charge to prevent excessive voltage ripple at

the input.