MCP1640CT-IMC datasheet(16/32 Pages) MICROCHIP

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MCP1640/B/C/D

DS20002234D-page 16

 2010-2015 Microchip Technology Inc.

The MCP1640/B/C/D is internally compensated, so

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, espe-

cially while stepping from light current loads (PFM

mode) to heavy current loads (PWM mode). Over-

shoots and undershoots during pulse load application

are reduced by adding a zero in the compensation

loop. A small capacitance (for example 100 pF) in par-

allel with an upper feedback resistor will reduce output

spikes, especially in PFM mode.

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 MCP1640/B/C/D is designed to be used with small

surface-mount inductors; the inductance value can

range from 2.2 µH to 10 µH. An inductance value of

4.7 µH is recommended to achieve a good balance

between

inductor

size,

converter

load

transient

response and minimized noise.

Several parameters are used to select the correct

inductor: maximum rated current, saturation current

and copper resistance (ESR). For boost converters, the

inductor current is much higher than the output current;

the average of the inductor current is equal to the input

current drawn from the input. The lower the inductor

ESR, the higher the efficiency of the converter. This is

a common trade-off in size versus efficiency.

Peak current is the maximum or the limit, and

saturation current typically specifies a point at which

the inductance has rolled off a percentage of the rated

value. This can range from a 20% to 40% reduction in

inductance. As inductance rolls off, the inductor ripple

current increases; as does the peak switch current. It is

important to keep the inductance from rolling off too

much, causing switch current to reach the peak limit.

TABLE 5-1:

CAPACITOR VALUE RANGE

CIN

COUT

Min.

4.7 µF

10 µF

Max.

—

100 µF

OUT

-------







Where:

dV = ripple voltage

dt = On time of the N-Channel switch

(D x 1/FSW)

TABLE 5-2:

MCP1640/B/C/D

RECOMMENDED INDUCTORS

Part Number

Size

WxLxH

(mm)

Coilcraft

EPL2014-472

4.7

0.23

1.06

2.0x2.0x1.4

EPL3012-472

4.7

0.165

1.1

3.0x3.0x1.3

MSS4020-472

4.7

0.115

1.5

4.0x4.0x2.0

LPS6225-472

4.7

0.065

3.2

6.0x6.0x2.4

Coiltronics®

SD3110

4.7

0.285

0.68

3.1x3.1x1.0

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

SD3812

4.7

0.256

1.13

3.8x3.8x1.2

SD25

4.7

0.0467

1.83

5.0x5.0x2.5

Würth Elektronik®

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

WE-TPC Type X

4.7

0.046

2.00

6.8x6.8x2.3

Sumida Corporation

CMH23

4.7

0.537

0.70

2.3x2.3x1.0

CMD4D06

4.7

0.216

0.75

3.5x4.3x0.8

CDRH4D

4.7

0.09

0.800

4.6x4.6x1.5

TDK-EPCOS

B82462A2472M000

4.7

0.084

2.00

6.0x6.0x2.5

B82462G4472M

4.7

0.04

1.8

6.3x6.3x3.0

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