TC1303B-1G0EMF datasheet(26/38 Pages) MICROCHIP

Part #	TC1303B-1G0EMF

Description	500 mA Synchronous Buck Regulator, 300 mA LDO with Power-Good Output

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26 / 38 page

TC1303A/TC1303B/TC1303C/TC1304

DS21949C-page 26

5.5

Inductor Selection

For most applications, a 4.7 µH inductor is recom-

mended to minimize noise. There are many different

magnetic core materials and package options to select

from. That decision is based on size, cost and accept-

able radiated energy levels. Toroid and shielded ferrite

pot cores will have low radiated energy, but tend to be

larger and higher is cost. With a typical 2.0 MHz

switching frequency, the inductor ripple current can be

calculated based on the following formulas.

EQUATION 5-2:

Duty cycle represents the percentage of switch-on

time.

EQUATION 5-3:

The inductor ac ripple current can be calculated using

the following relationship:

EQUATION 5-4:

Solving for ∆IL = yields:

EQUATION 5-5:

When considering inductor ratings, the maximum DC

current rating of the inductor should be at least equal to

the maximum buck regulator load current (IOUT1), plus

one half of the peak-to-peak inductor ripple current (1/

2*

ΔIL). The inductor DC resistance can add to the

buck converter I2R losses. A rating of less than 200 mΩ

is recommended. Overall efficiency will be improved by

using lower DC resistance inductors.

TABLE 5-2:

TC1303A, TC1303B, TC1303C,

TC1304 RECOMMENDED

INDUCTOR VALUES

5.6

Thermal Calculations

5.6.1

BUCK REGULATOR OUTPUT

(VOUT1)

The TC1303/TC1304 is available in two different 10-pin

packages (MSOP and 3x3 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 TC1303/TC1304 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 (Section 2.0 “Typical Perfor-

mance Curves”), the internal power dissipation is

estimated below:

EQUATION 5-6:

The first term is equal to the input power (definition of

efficiency, POUT/PIN = Efficiency). The second term is

equal to the delivered power. The difference is internal

power dissipation. This is an estimate assuming that

most of the power lost is internal to the TC1303B.

There is some percentage of power lost in the buck

inductor, with very little loss in the input and output

capacitors.

DutyCycle

V

OUT

V

IN

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

=

T

ON

DutyCycle

1

F

SW

----------

×

=

Where:

FSW = Switching Frequency.

V

L

ΔI

L

Δt

--------

×

=

Where:

VL = voltage across the inductor (VIN – VOUT)

∆t = on-time of P-channel MOSFET

ΔI

L

V

L

------

Δt

×

=

Part

Number

Value

(µH)

DCR

Ω

(MAX)

MAX

IDC (A)

Size

WxLxH (mm)

Coiltronics®

SD10

2.2

0.091

1.35 5.2, 5.2, 1.0 max.

SD10

3.3

0.108

1.24 5.2, 5.2, 1.0 max.

SD10

4.7

0.154

1.04 5.2, 5.2, 1.0 max.

Coiltronics

SD12

2.2

0.075

1.80 5.2, 5.2, 1.2 max.

SD12

3.3

0.104

1.42 5.2, 5.2, 1.2 max.

SD12

4.7

0.118

1.29 5.2, 5.2, 1.2 max.

Sumida Corporation®

CMD411

2.2

0.116

0.950 4.4, 5.8, 1.2 max.

CMD411

3.3

0.174 0.770 4.4, 5.8, 1.2 max.

CMD411

4.7

0.216 0.750 4.4, 5.8, 1.2 max.

Coilcraft®

1008PS

4.7

0.35

1.0

3.8, 3.8, 2.74 max.

1812PS

4.7

0.11

1.15 5.9, 5.0, 3.81 max

V

OUT1

I

OUT1

×

Efficiency

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

⎝⎠

⎛⎞

V

OUT1

I

OUT1

×

()

–

P

Dissipation

=

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