MCP16252 datasheet(15/34 Pages) MICROCHIP

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 2013 Microchip Technology Inc.

DS25173A-page 15

MCP16251/2

5.4

Output Capacitor Selection

The output capacitor helps provide a stable output

voltage during sudden load transients and reduces the

output voltage ripple. As with the input capacitor, X5R

and X7R ceramic capacitors are well suited for this

application. Using other capacitor types (aluminum or

tantalum) with large ESR has impact for the converter's

efficiency (see AN1337) and maximum output power.

The MCP16251/2 is internally compensated, so the

output capacitance range is limited. See Table 5-1 for

the recommended output capacitor range.

An output capacitance higher than 10 µF adds a better

load

step

response

and

high-frequency

noise

attenuation, especially while stepping from light current

loads (PFM mode) to heavy current loads (PWM

mode). A minimum of 20 µF output capacitance is

mandatory while the output drives load steps between

heavy load levels. In addition, 2 x 10 µF output

capacitors ensure a better recovery of the output after

a short period of overloading.

While the N-Channel switch is on, the output current is

supplied by the output capacitor COUT. The amount of

output capacitance and equivalent series resistance

will have a significant effect on the output ripple

voltage. While COUT provides load current, a voltage

drop also appears across its internal ESR that results

in ripple voltage.

EQUATION 5-2:

Table 5-1 contains the recommended range for the

input and output capacitor value.

5.5

Inductor Selection

The MCP16251/2 is designed to be used with small

surface mount inductors; the inductance value can

range from 2.2 µH to 6.8 µH. An inductance value of

4.7 µH is recommended to achieve a good balance

between the inductor size, converter load transient

response and minimized noise.

TABLE 5-1:

CAPACITOR VALUE RANGE

CIN

COUT

Minimum

4.7 µF

10 µF

Maximum

none

47 µF

OUT

-------







Where:

dV = the ripple voltage and

ON time of the N-Channel switch

(D x 1/FSW, D is duty cycle)

TABLE 5-2:

MCP16251/2 RECOMMENDED

INDUCTORS

Part

Number

Value

(µH)

DCR

 (typ)

ISAT

(A)

Size

WxLxH (mm)

Coiltronics®

SD3112

4.7

0.246

0.80

3.1x3.1x1.2

SD3114

4.7

0.251

1.14

3.1x3.1x1.4

SD3118

4.7

0.162

1.31

3.8x3.8x1.2

SD25

4.7

0.0467

1.83

5.0x5.0x2.5

Wurth® Group

WE-TPC

Type Tiny

4.7

0.100

1.7

2.8x2.8x2.8

WE-TPC

Type TH

4.7

0.200

0.8

2.8x2.8x1.35

WE-TPC

Type S

4.7

0.105

0.90

3.8x3.8x1.65

WE-TPC

Type M

4.7

0.082

1.65

4.8x4.8x1.8

Sumida Corporation

CMD4D06

4.7

0.216

0.75

3.5x4.3x2

CDRH4D

4.7

0.09

0.800

4.6x4.6x1.5

Coilcraft

XPL2010

4.7

0.336

0.75

1.9x2x1.0

ME3220

4.7

0.190

1.5

2.5x3.2x2.0

XFL3010

4.7

0.217

1.1

3x3x1.0

XFL3012

4.7

0.143

1.0

3x3x1.2

EPL3012

4.7

0.165

1.0

3x3x1.3

LPS4018

4.7

0.125

1.8

4x4x1.8

XFL4020

4.7

0.052

2.0

4x4x2.1

TDK Corporation

VLS3015ET

-4R7M

4.7

0.113

1.1

3x3x1.5

B82462

G4472M

4.7

0.04

1.8

6x6x3

B82462

A4472M

4.7

0.08

2.8

6x6x3

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