MP8763 — 12A, 18V, SYNCHRONOUS STEP-DOWN CONVERTER

MP8763 Rev. 1.3

www.MonolithicPower.com

19

6/21/2016

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below

the

maximum

switch-current

limit.

Calculate the inductance value as:

)

V

V

(

I

f

V

L

IN

OUT

L

SW

OUT

−

×

∆

×

=

1

(27)

current.

Choose an inductor that will not saturate under

the maximum inductor peak current. The peak

inductor current can be calculated as:

)

V

V

(

L

f

V

I

I

IN

OUT

SW

OUT

OUT

LP

−

×

×

×

+

=

1

2

(28)

Table 1 lists a few highly-recommended high-

efficiency inductors.

Table 1: Inductor Selection Guide

Part Number

Manufacturer

Inductance

(µH)

DCR

(m )

Current

Rating (A)

Dimensions

L × W × H (mm

Switching

Frequency

(kHz)

744325072

Wurth

0.72

1.35

35

10.2 × 10.5 × 4.7

500

FDA1055-1R5M

TOKO

1.5

2.8

24

10.6 x 10.8 x 5.5

500

744325180

Wurth

1.8

3.5

18

10.2 × 10.5 × 4.7

500

Typical Design Parameters

Tables 2 and 3 list recommended component

values for typical output voltages (1V, 2.5V, 3.3V)

and switching frequency (500kHz). Refer to

Table 2 for design cases without external ramp

compensation and Table 3 for design cases with

external ramp compensation. An external ramp is

not needed when using high-ESR capacitors,

such as electrolytics or POSCAPs. Use an

external ramp when using low-ESR capacitors,

such as ceramic capacitors. For cases not listed

in

this

datasheet,

conctact

a

local

sales

representative for an Excel spreadsheet to assist

with the calculation.

(V)

L

(µH)

R1

(k )

R2

(k )

R7

(8)

(k )

1

0.72

12.7

20

357

2.5

1.5

61.9

20

825

3.3

1.8

88.7

20

1083

(V)

L

(µH)

R1

(k )

R2

(k )

R4

(k )

C4

(pF)

R7

(8)

(k )

1

0.72

12.7

20

750

220

357

2.5

1.5

64.9

20

1000

220

825

3.3

1.8

93.1

20

1200

220

1083

Notes:

is a little different from equation (3) due to the voltage

drop on MOSFET.