Microchip Technology ADM00427 Ficha De Dados

DS22284A-page 20

© 2011 Microchip Technology Inc.

5.0.6

INDUCTOR SELECTION

The MCP16323 is designed to be used with small
surface mount inductors. Several specifications should
be considered prior to selecting an inductor. To
optimize system performance, low ESR inductors
should be used.

An inductor saturation rating minimum of 3.255A is
recommended. A trade-off between size, cost and
efficiency is made to achieve the desired results.

5.0.7

BOOST CAPACITOR

The boost capacitor is used to supply current for the
internal high-side drive circuitry that is above the input
voltage. The boost capacitor must store enough energy
to completely drive the high-side switch on and off. A
22 nF X5R or X7R capacitor is recommended for all
applications. The boost capacitor maximum voltage is
5.5V, so a 6.3V or 10V rated capacitor is
recommended.

5.0.8

THERMAL CALCULATIONS

The MCP16323 is available in a 3x3 QFN-16 package.
By calculating the power dissipation and applying the
package thermal resistance (θ

JA

), the junction

temperature is estimated. The maximum continuous
junction temperature rating for the MCP16323 is
+125°C.
To quickly estimate the internal power dissipation for
the switching step-down regulator, an empirical
calculation using measured efficiency can be used.
Given the measured efficiency, the internal power
dissipation is estimated in 

. This power

dissipation includes all internal and external
component losses. For a quick internal estimate,
subtract the estimated inductor ESR loss from the P

DIS

calculation in 

The difference between the first term, input power, and
the second term, power delivered, is the total system
power dissipation. The inductor losses are estimated
by P

L

= I

OUT

2

x L

ESR

.

C

OUT

33 µF

None

V

IN

= 12V

V

OUT

= 3.3V

I

OUT

= 3A

L = 4.7 µH

Inductor ripple current = 509 mA
Inductor peak current = 3.255A

Ω)

MSS6132-472

4.7

0.056 2.84

6.1x6.1x3.2

LPS6225-472

4.7

0.065

3.2

6.2x6.2x2.5

MSS7341-502

4.7

0.024 3.16

7.3x7.3x4.1

DO1813H-472

4.7

0.054

2.6

8.89x6.1x5.0

7447785004

4.7

0.06

2.5

5.9x6.2x3.3

7447786004

4.7

0.057

2.8

5.9x6.2x5.1

7447789004

4.7

0.033

3.9

7.3x3.2x1.5

B82464G2

4.7

0.033

3.1 10.4x10.4x3.0

B82464A2

4.7

0.03

4.5 10.4x10.4x3.0

Δ

×

Δ

V

IN

= 12V

V

OUT

= 5.0V

I

OUT

= 3 A

Efficiency = 88%

Total System Dissipation = 2.05 W

L

ESR

= 0.02

Ω

P

L

= 180 mW

MCP16323 internal power dissipation estimate:

P

DIS

– P

L

= 1.87 W

θ

JA

= 38.5°C/W

Estimated Junction = +71.995°C

θ

JA

 = 38.5°C/W for a 4-layer FR4 Printed Circuit

Board with a 13.5 in

2

, 1 oz internal copper ground

plane.

A smaller ground plane will result in a larger 

θ

JA

temperature rise.  

×

×

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