Operational Lifetime

ContinuousJunctionTemperature

C

°

-

1000

100

10

1

80

90

100

110

120

130

140

150

160

170

180

ADS5474

It is important for applications that anticipate running continuously for long periods of time near the

maximum-rated ambient temperature of +85°C to consider the data shown in Figure 50. Referring to the Thermal

Characteristics table, the worst-case operating condition with no airflow has a thermal rise of 23.7°C/W. At

approximately 2.5 W of normal power dissipation, at a maximum ambient of +85°C with no airflow, the junction

temperature of the ADS5474 reaches approximately +85°C + 23.7°C/W × 2.5 W = +144°C. Being even more

conservative and accounting for the maximum possible power dissipation that is ensured (2.797 W), the junction

temperature becomes nearly +150°C. As Figure 50 shows, this performance limits the expected lifetime of the

ADS5474. Operation at +85°C continuously may require airflow or an additional heatsink in order to decrease the

internal junction temperature and increase the expected lifetime (because of electromigration failures). An airflow

of 250 LFM (linear feet per minute) reduces the thermal resistance to 16.4°C/W and, therefore, the maximum

junction temperature to +131°C, assuming a worst-case of 2.797 W and +85°C ambient.

The ADS5474 performance over temperature is quite good and can be seen starting in Figure 21. Though the

typical plots show good performance at +100°C, the device is only rated from –40°C to +85°C. For continuous

operation at temperatures near or above the maximum, the expected primary negative effect is a shorter device

lifetime because of the electromigration failures at high junction temperatures. The maximum recommended

continuous junction temperature is +150°C.

Figure 50. Operating Life Derating Chart, Electromigration Fail Mode

Copyright © 2007–2008, Texas Instruments Incorporated

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