MCP1603-ADJISLASHOS datasheet(15/26 Pages) MICROCHIP

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DS22042A-page 15

MCP1603

Table 5-1 contains the recommend range for the output

capacitor value.

5.6

Inductor Selection

When using the MCP1603, the inductance value can

range from 3.3 µH to 10 µH. An inductance value of

4.7 µH is recommended to achieve a good balance

between converter load transient response and mini-

mized noise.

The value of inductance is selected to achieve a

desired amount of ripple current. It is reasonable to

assume a ripple current that is 20% of the maximum

load current. The larger the amount of ripple current

allowed, the larger the output capacitor value becomes

to meet ripple voltage specifications. The inductor

ripple current can be calculated according to the follow-

ing equation.

EQUATION 5-4:

When considering inductor ratings, the maximum DC

current rating of the inductor should be at least equal to

the maximum load current, plus one half the peak-to-

peak inductor ripple current (1/2 *

ΔIL). The inductor DC

resistance adds to the total converter power loss. An

inductor with a low DC resistance allows for higher

converter efficiency.

5.7

Thermal Calculations

The MCP1603 is available in two different packages

(TSOT-23 and 2x3 DFN). By calculating the power

dissipation and applying the package thermal

resistance, (

θJA), the junction temperature is

estimated.

The

maximum

continuous

junction

temperature rating for the MCP1603 is +125°C.

To quickly estimate the internal power dissipation for

the switching buck regulator, an empirical calculation

using measured efficiency can be used. Given the

measured efficiency, the internal power dissipation is

estimated by:

EQUATION 5-5:

The difference between the first term, input power

dissipation, and the second term, power delivered, is

the internal power dissipation. This is an estimate

assuming that most of the power lost is internal to the

MCP1603. There is some percentage of power lost in

the buck inductor, with very little loss in the input and

output capacitors.

TABLE 5-1:

CAPACITOR VALUE RANGE

CIN

COUT

Minimum

4.7 µF

Maximum

—

22 µF

ΔI

VOUT

FSW L

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

VOUT

VIN

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

–

⎝⎠

⎛⎞

Where:

FSW = Switching Frequency

TABLE 5-2:

MCP1603 RECOMMENDED

INDUCTORS

Part

Number

Value

(µH)

DCR

(max)

ISAT

(A)

Size

WxLxH (mm)

Coiltronics®

SD3110

3.3

0.195

0.81

3.1x3.1x1.0

SD3110

4.7

0.285

0.68

3.1x3.1x1.0

SD3110

6.8

0.346

0.58

3.1x3.1x1.0

SD3812

3.3

0.159

1.40

3.8x3.8x1.2

SD3812

4.7

0.256

1.13

3.8x3.8x1.2

SD3812

6.8

0.299

0.95

3.8x3.8x1.2

Würth Elektronik®

WE-TPC

Type XS

3.3

0.225

0.72

3.3x3.5x0.95

WE-TPC

Type XS

4.7

0.290

0.50

3.3x3.5x0.95

WE-TPC

Type S

4.7

0.105

0.90

3.8x3.8x1.65

WE-TPC

Type S

6.8

0.156

0.75

3.8x3.8x1.65

Sumida®

CMD4D06

3.3

0.174

0.77

3.5x4.3x0.8

CMD4D06

4.7

0.216

0.75

3.5x4.3x0.8

CMD4D06

6.8

0.296

0.62

3.5x4.3x0.8

VOUT IOUT

Efficiency

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

⎝⎠

⎛⎞

VOUT IOUT

()

–

PDiss

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