MPQ8632-8 datasheet(27/46 Pages) MPS

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MPQ8632 HIGH EFFICIENCY 18V SYNCHRONOUS STEP-DOWN CONVERTER FAMILY FOR 4A TO 20A

MPQ8632 Rev.1.24

www.MonolithicPower.com

8/28/2013

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

The ESR dominates the switching-frequency

impedance for POSCAPs,. The ESR ramp

voltage is high enough to stabilize the system.

thus eliminating the need for an external ramp.

Select a

minimum ESR value around 12mΩ to

ensure stable operation. For simplification, the

output ripple can be approximated as:

ESR

OUT

)

(











(26)

Inductor

The inductor supplies constant current to the

output load while being driven by the switching

input voltage. A larger value inductor results in

less ripple current and lower output ripple voltage,

but is larger physical size, has a higher series

resistance,

and/or

lower

saturation

current.

Generally, select an inductor value that allows

the inductor peak-to-peak ripple current to 30%

to 40% of the maximum switch current limit. Also,

design for a peak inductor current that is below

the maximum switch current limit. Calculate the

inductance value as:

)

(

OUT











(27)

Whe

re ΔI

is the peak-to-peak inductor ripple

current.

Choose an inductor that will not saturate under

the maximum inductor peak current. The peak

inductor current can be calculated as:

)

(

OUT









(28)

Table 2 lists a few highly-recommended high-

efficiency inductors.

Table 2

—Inductor Selection Guide

Part Number

Manufacturer

Inductance

(µH)

DCR

(mΩ)

Current

Rating (A)

Dimensions

L x W x H (mm

Switching

Frequency

(kHz)

744325072

Wurth

0.72

1.35

10.2 x 10.5 x 4.7

500

FDU1250C-1R0M

TOKO

1.72

31.3

13.3 x 12.1 x 5

500

FDA1055-1R5M

TOKO

1.5

2.8

11.6 x 10.8 x 5.5

500

744325180

Wurth

1.8

3.5

10.2 x 10.5 x 4.7

500

FDA1055-2R2M

TOKO

2.2

3.94

20.6

11.6 x 10.8 x 5.5

500

FDA1055-3R3M

TOKO

3.3

5.92

15.6

11.6 x 10.8 x 5.5

500

HC7-3R9-R

Cooper

3.9

7.9

10.6

13.8 x 13 x 5.5

500

Typical Design Parameter Tables

The

following

tables

include

recommended

component values for typical output voltages (1V,

2.5V, 3.3V) and switching frequency (500kHz).

Refer to Tables 3-9 for design cases without

external ramp compensation. And Tables 10-16

are

for

design

cases

with

external

ramp

compensation. An external ramp is not needed

when using high-ESR output capacitors, such as

electrolytic or POSCAPs. Use an external ramp

when using low-ESR capacitors, such as ceramic

capacitors. For cases not listed in this datasheet,

an excel spreadsheet provided by local sales

representatives can assist with the calculations.

Table 3

—MPQ8632-4, F

SW=500kHz, VIN=12V

VOUT

(V)

(

μH)

Ω)

1.8

13.3

357

2.5

3.3

63.4

887

3.3

3.9

1200

Table 4

—MPQ8632-6, F

SW=500kHz, VIN=12V

VOUT

(V)

(

μH)

Ω)

13.3

357

2.5

2.2

63.4

887

3.3

1200

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