MCP1623 datasheet(14/26 Pages) MICROCHIP

14 / 26 page

MCP1623/24

DS41420A-page 14

 2010 Microchip Technology Inc.

5.5

Inductor Selection

The MCP1623/24 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 can be much higher than the output

current. The lower the inductor ESR, the higher the

efficiency of the converter, a common trade-off in size

versus efficiency.

Peak current is the maximum or limit, and saturation

current typically specifies a point at which the induc-

tance has rolled off a percentage of the rated value.

This can range from a 20% to 40% reduction in induc-

tance. As inductance rolls off, the inductor ripple cur-

rent 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.

5.6

Thermal Calculations

By calculating the power dissipation and applying the

package thermal resistance, (

JA), the junction temper-

ature is estimated. The maximum continuous junction

temperature rating for the MCP1623/24 is +125oC.

To quickly estimate the internal power dissipation for

the switching boost regulator, an empirical calculation

using measured efficiency can be used. Given the

measured efficiency, the internal power dissipation is

estimated by Equation 5-3.

EQUATION 5-3:

The difference between the first term, input power, and

the second term, power delivered, is the internal

MCP1623/24 power dissipation. This is an estimate

assuming that most of the power lost is internal to the

MCP1623/24 and not CIN, COUT and the inductor.

There is some percentage of power lost in the boost

inductor, with very little loss in the input and output

capacitors. For a more accurate estimation of internal

power dissipation, subtract the IINRMS2*LESR power

dissipation.

TABLE 5-2:

MCP1623/24 RECOMMENDED

INDUCTORS

Part

Number

Value

(µH)

DCR

 (typ)

ISAT

(A)

Size

WxLxH (mm)

Coilcraft®

ME3220

4.7

0.190

1.5

2.5x3.2x2.0

LPS3015

4.7

0.200

1.2

3.0x3.0x1.5

EPL3012

4.7

0.165

1.0

3.0x3.0x1.3

XPL2010

4.7

0.336

0.75

1.9x2.0x1.0

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

Part

Number

Value

(µH)

DCR



(max)

ISAT

(A)

Size

WxLxH (mm)

Wurth 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

Part

Number

Value

(µH)

DCR



(max)

ISAT

(A)

Size

WxLxH (mm)

Sumida®

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

EPCOS®

B82462A2

472M000

4.7

0.084

2.00

6.0x6.0x2.5

B82462G4

472M

4.7

0.04

1.8

6.3x6.3x3.0

VOUT IOUT



Efficiency

-------------------------------





VOUT IOUT





–

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