MP8714 – 17V, 10A, SYNCHRONOUS, STEP-DOWN CONVERTER

MP8714 Rev.1.0

www.MonolithicPower.com

15

12/27/2016

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© 2016 MPS. All Rights Reserved.

APPLICATION INFORMATION

Setting the Output

The reference voltage and external resistor

divider can set the output voltage through FB.

The feedback resistors R1 and R3 set the

feedback loop bandwidth with the internal

compensation capacitor. Choose a value for R1

first, and then calculate R2 with Equation (2):

1

V

V

R1

R2

REF

OUT





(2)

The T-type network is highly recommended

(see Figure 6).

Figure 6: T-Type Network

Table 1 lists the recommended feedback

resistors value for common output voltages.

Table 1: Resistor Selection for Common Output

Voltages

(9)

VOUT

(V)

R1

(kΩ)

R2

(kΩ)

R3

(kΩ)

C6

(pF)

L

(µH)

0.9

80.6

(1%)

162

(1%)

51

(1%)

22

1.5

1.0

80.6

(1%)

120

(1%)

51

(1%)

22

1.5

1.2

80.6

(1%)

80.6

(1%)

40.2

(1%)

22

1.5

2.5

60.4

(1%)

19.1

(1%)

30

(1%)

22

2.2

3.3

60.4

(1%)

13.3

(1%)

20

(1%)

33

3.3

5

60.4

(1%)

8.25

(1%)

20

(1%)

33

3.3

NOTE:

9)

The recommended parameters are based on a 12V input

voltage and 22µFx4 output capacitor. Different input voltage

and output capacitor values may affect the selection of R1,

R2, R3, and C6. For other components’ parameters, please

refer to the Typical Application Circuits on page 18.

Selecting the Inductor

Use a 0.47µH to 10µH inductor with a DC

current rating at least 25% higher than the

maximum load current for most applications.

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 (3):

OUT

IN

OUT

1

IN

L

OSC

V(V

V

)

L

VI

f





 

(3)

Choose the inductor ripple current to be

approximately 30% of the maximum load

current. The maximum inductor peak current

can be calculated with Equation (4):

2

I

I

I

L

LOAD

)

MAX

(

L







(4)

Use a larger inductor for improved efficiency

under light-load conditions below 100mA.

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 low ESR capacitors for the best

performance. Ceramic capacitors with X5R or

X7R dielectrics are recommended for best

results because of their low ESR and small

temperature coefficients. For most applications,

use two 22µF 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 (5):

























IN

OUT

IN

OUT

LOAD

1

C

V

V

1

V

V

I

I

(5)

The worst-case condition occurs at VIN =

2VOUT, shown in Equation (6):

2

I

I

LOAD

1

C



(6)