MP2276

– 16V, 8A, HIGH EFFICIENCY, SYNC, STEP-DOWN CONVERTER

MP2276 Rev.1.0

www.MonolithicPower.com

18

3/22/2017

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

© 2017 MPS. All Rights Reserved.

APPLICATION INFORMATION

Output Voltage Setting

Choose a proper value for R1 in the range of

1kΩ to 100kΩ. Then determine R2 with

Equation (6):

REF

21

O

REF

V

R (k )

R (k )

VV

 







(6)

To optimize the load transient response, a feed-

system, which helps improve loop responses.

located around 20kHz - 60kHz.

Table 2 lists the recommended resistor values

for common output voltages.

Table 2: Resistor Selection for Common Output

R1(kΩ)

R2(kΩ)

1

2

8.06

1.2

2

4.02

1.8

10

8.06

2.5

10

4.7

3.3

10

3.16

5

10

1.91

NOTE:

6)

For additional component parameters, please refer to the

Typical Application Circuits on page 21 to page 22.

Selecting the Input Capacitor

The input current to the step-down converter is

discontinuous

and

therefore

requires

a

capacitor to supply AC current to the step-down

converter

while

maintaining

the

DC

input

voltage. Use ceramic capacitors for the best

performance. During layout, place the input

capacitors as close to VIN as possible.

The capacitance can vary significantly with the

temperature. Capacitors with X5R and X7R

ceramic dielectrics are recommended because

they are fairly stable over a wide temperature

range.

The capacitors must also have a ripple current

rating that exceeds the

converter’s maximum

input ripple current. Estimate the input ripple

current with Equation (7):

)

V

V

1

(

V

V

I

I

IN

OUT

IN

OUT

OUT

CIN









(7)

shown in Equation (8):

2

I

I

OUT

(8)

For simplification, choose an input capacitor

with an RMS current rating that exceeds half

the maximum load current.

The input capacitance value determines the

converter

input

voltage

ripple.

Select

a

capacitor value that meets any input voltage

ripple requirement.

Estimate the input voltage ripple with Equation

(9):

)

V

V

1

(

V

V

C

F

I

V

IN

OUT

IN

OUT

IN

SW

OUT

IN













(9)

shown in Equation (10):

IN

SW

OUT

IN

C

F

I

4

1

V









(10)

Selecting the Output Capacitor

The output capacitor maintains the DC output

voltage. Use ceramic capacitors or POSCAPs.

Estimate the output voltage ripple with Equation

(11):

)

8

1

(

)

1

(

OUT

SW

ESR

IN

OUT

SW

OUT

OUT

C

F

R

V

V

L

F

V

V



















(11)

When

using

ceramic

capacitors,

the

capacitance dominates the impedance at the

switching frequency. The capacitance also

dominates

the

output

voltage

ripple.

For

simplification, estimate the output voltage ripple

with Equation (12):

)

V

V

1

(

C

L

F

8

V

V

IN

OUT

OUT

2

SW

OUT

OUT















(12)

For

POSCAPs,

the

ESR

dominates

the

switching

frequency

impedance.

For

simplification,

the

output

ripple

can

be

approximated with Equation (13):

ESR

IN

OUT

SW

OUT

OUT

R

)

V

V

1

(

L

F

V

V













(13)