ADP3000AR datasheet(12/16 Pages) AD

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ADP3000

Rev. A | Page 12 of 16

Step-Down

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SAT

CESAT

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where:

ISW is ILIMIT when the current limit is programmed externally;

otherwise, ISW is the maximum inductor current.

VCE(SAT) is 1.2 V (typical value). Check this value by applying ISW

to Figure 10.

VO is the output voltage.

IO is the output current.

VIN is the input voltage.

D is 0.75 (typical duty ratio for a single switching cycle).

IQ is 500 µA (typical shutdown quiescent current).

β is 30 (typical forced beta).

The temperature rise can be calculated using the following

equation:

∆

where:

∆T is temperature rise.

PD is device power dissipation.

θJA is thermal resistance (junction-to-ambient).

For example, consider a boost converter with the following

specifications:

VIN is 2 V.

VO is 3.3 V.

IO is 180 mA.

ISW is 0.8 A (externally programmed).

Using the step-up power dissipation equation:

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∆T is 185 mW (170°C/W) = 31.5°C, using the R-8 package.

∆T is 185 mW (120°C/W) = 22.2°C, using the N-8 package.

At a 70°C ambient, the die temperature would be 101.45°C for

the R-8 package and 92.2°C for the N-8 package. These junction

temperatures are well below the maximum recommended

junction temperature of 125°C.

Finally, the die temperature can be decreased up to 20% by

using a large metal ground plate as ground pickup for the

ADP3000.

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