AD590JCPZ-R5 datasheet(9/16 Pages) AD

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Data Sheet

AD590

Rev. G | Page 9 of 16

As an example, for the TO-52 package, θJC is the thermal

resistance between the chip and the case, about 26°C/W. θCA is

the thermal resistance between the case and the surroundings

and is determined by the characteristics of the thermal

connection. Power source P represents the power dissipated

on the chip. The rise of the junction temperature, TJ, above the

ambient temperature, TA, is

TJ − TA = P(θJC + θCA)

(1)

Table 4 gives the sum of θJC and θCA for several common

thermal media for both the H and F packages. The heat sink

used was a common clip-on. Using Equation 1, the temperature

rise of an AD590 H package in a stirred bath at 25°C, when

driven with a 5 V supply, is 0.06°C. However, for the same

conditions in still air, the temperature rise is 0.72°C. For a given

supply voltage, the temperature rise varies with the current and

is PTAT. Therefore, if an application circuit is trimmed with the

sensor in the same thermal environment in which it is used, the

scale factor trim compensates for this effect over the entire

temperature range.

Table 4. Thermal Resistance

θJC + θCA

(°C/Watt)

τ (sec)1

Medium

Aluminum Block

0.6

0.1

Stirred Oil2

1.4

0.6

Moving Air3

With Heat Sink

–

5.0

–

Without Heat Sink

115

190

13.5

10.0

Still Air

With Heat Sink

191

–

108

–

Without Heat Sink

480

650

1 τ is dependent upon velocity of oil; average of several velocities listed above.

2 Air velocity @ 9 ft/sec.

3 The time constant is defined as the time required to reach 63.2% of an

instantaneous temperature change.

The time response of the AD590 to a step change in

temperature is determined by the thermal resistances and the

thermal capacities of the chip, CCH, and the case, CC. CCH is

about 0.04 Ws/°C for the AD590. CC varies with the measured

medium, because it includes anything that is in direct thermal

contact with the case. The single time constant exponential

curve of Figure 16 is usually sufficient to describe the time

response, T (t). Table 4 shows the effective time constant, τ, for

several media.

Figure 16. Time Response Curve

TFINAL

TINITIAL



TIME

T(t) = TINITIAL + (TFINAL – TINITIAL) × (1 – e–t/)

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