AD9550 datasheet(17/20 Pages) AD

17 / 20 page

AD9550

Rev. 0 | Page 17 of 20

APPLICATIONS INFORMATION

THERMAL PERFORMANCE

The AD9550 is specified for case temperature (TCASE). To ensure

that TCASE is not exceeded, use an airflow source.

The following equation determines the junction temperature on

the application printed circuit board (PCB):

TJ = TCASE + (ΨJT × PD)

where:

TJ is the junction temperature (°C).

TCASE is the case temperature (°C) measured by the customer

at the top center of the package.

ΨJT is the value indicated in Table 11.

PD is the power dissipation (see Table 1 for the power

consumption parameters).

Values of θJA are provided for package comparison and PCB design

considerations. θJA can be used for a first-order approximation

of TJ using the following equation:

TJ = TA + (θJA × PD)

where TA is the ambient temperature (°C).

Values of θJC are provided for package comparison and PCB

design considerations when an external heat sink is required.

Values of θJB are provided for package comparison and PCB

design considerations.

Table 11. Thermal Parameters for the 32-Lead LFCSP

Symbol

Description

Value1

Unit

Junction-to-ambient thermal

resistance, 0 m/sec airflow per

JEDEC JESD51-2 (still air)

41.6

°C/W

JMA

Junction-to-ambient thermal

resistance, 1.0 m/sec airflow per

JEDEC JESD51-6 (moving air)

36.4

°C/W

JMA

Junction-to-ambient thermal

resistance, 2.5 m/sec airflow per

JEDEC JESD51-6 (moving air)

32.6

°C/W

Junction-to-board thermal

resistance, 0 m/sec airflow per

JEDEC JESD51-8 (still air)

24.2

°C/W

Junction-to-board characterization

parameter, 0 m/sec airflow per

JEDEC JESD51-6 (still air)

22.9

°C/W

Junction-to-case thermal resistance

4.8

°C/W

Junction-to-top-of-package

characterization parameter, 0 m/sec

airflow per JEDEC JESD51-2 (still air)

0.5

°C/W

1 Results are from simulations. The PCB is a JEDEC multilayer type. Thermal

performance for actual applications requires careful inspection of the

conditions in the application to determine whether they are similar to those

assumed in these calculations.

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