AD590LF Datasheet AD590KF/883B, AD590JF, AD590KH | P10-P12

Data Sheet AD590

Rev. G | Page 9 of 16

As an example, for the TO-52 package, θ

is the thermal

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

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, T

, above the

ambient temperature, T

, is

− T

= P(θ

+ θ

) (1)

Table 4 g ives t he sum of θ

and θ

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

+ θ

(°C/Watt) τ (sec)

Medium H F H F

Aluminum Block 30 10 0.6 0.1

Stirred Oil

42 60 1.4 0.6

Moving Air

With Heat Sink 45 – 5.0 –

Without Heat Sink 115 190 13.5 10.0

Still Air

With Heat Sink 191 – 108 –

Without Heat Sink 480 650 60 30

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

Air velocity @ 9 ft/sec.

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, C

, and the case, C

. C

about 0.04 Ws/°C for the AD590. C

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

00533-013

SENSED TEMPERATURE

FINAL

INITIAL

 4

TIME

T(t) = T

INITIAL

+ (T

FINAL

– T

INITIAL

) × (1 – e

–t/

)

AD590 Data Sheet

Rev. G | Page 10 of 16

GENERAL APPLICATIONS

Figure 17 shows a typical use of the AD590 in a remote

temperature sensing application. The AD590 is used as a

thermometer circuit that measures temperature from −55°C to

+150°C, with an output voltage of 1 mV/°K. Because the

AD590 measures absolute temperature (its nominal output is

1 mA/K), the output must be offset by 273.2 mA to read out in

degrees Celsius.

Figure 17. Variable Scale Display

Connecting several AD590 units in series, as shown in Figure 18,

allows the minimum of all the sensed temperatures to be

indicated. In contrast, using the sensors in parallel yields the

average of the sensed temperatures.

Figure 18. Series and Parallel Connection

The circuit in Figure 19 demonstrates one method by which

differential temperature measurements can be made. R1 and R2

can be used to trim the output of the op amp to indicate a

desired temperature difference. For example, the inherent offset

between the two devices can be trimmed in. If V+ and V− are

radically different, then the difference in internal dissipation

causes a differential internal temperature rise. This effect can be

used to measure the ambient thermal resistance seen by the

sensors in applications such as fluid-level detectors or anemometry.

Figure 19. Differential Measurements

Figure 20 is an example of a cold junction compensation circuit

for a Type J thermocouple using the AD590 to monitor the

reference junction temperature. This circuit replaces an ice-bath

as the thermocouple reference for ambient temperatures

between 15°C and 35°C. The circuit is calibrated by adjusting R

for a proper meter reading with the measuring junction at a

known reference temperature and the circuit near 25°C. Using

components with the TCs as specified in Figure 20, compensation

accuracy is within ±0.5°C for circuit temperatures between 15°C

and 35°C. Other thermocouple types can be accommodated with

different resistor values. Note that the TCs of the voltage

reference and the resistors are the primary contributors to error.

Figure 20. Cold Junction Compensation Circuit for Type J Thermocouple

AD590

–

00533-014

0.1% LOW

TCR RESISTOR

1mV/k

00533-015

AD590

–

AD590

–

AD590

–

MIN

10kΩ

(0.1%)

–

AD590

–

AVG

333.3Ω

(0.1%)

–

15V

00533-016

AD590L

–

AD590

–

10kΩ

5MΩ

50kΩ

V+

(T1 – T2) × (10mV/°C)

V–

OP177

–

00533-017

–

REFERENCE

JUNCTION

IRON

–

7.5V

AD590

AD580

CONS

TAN

MEASURING

JUNCTION

RESIS

ORS ARE 1%, 50ppm/°C

METER

–

52.3Ω

8.66k

Ω

OUT

Ω

Data Sheet AD590

Rev. G | Page 11 of 16

Figure 21 is an example of a current transmitter designed to be

used with 40 V, 1 kΩ systems; it uses its full current range of 4

to 20 mA for a narrow span of measured temperatures. In this

example, the 1 µA/K output of the AD590 is amplified to

1 mA/°C and offset so that 4 mA is equivalent to 17°C and

20 mA is equivalent to 33°C. R

is trimmed for proper reading

at an intermediate reference temperature. With a suitable choice

of resistors, any temperature range within the operating limits

of the AD590 can be chosen.

Figure 21. 4 to 20 mA Current Transmitter

Figure 22 is an example of a variable temperature control circuit

(thermostat) using the AD590. R

and R

are selected to set the

high and low limits for R

SET

. R

SET

could be a simple pot, a

calibrated multiturn pot, or a switched resistive divider. Powering

the AD590 from the 10 V reference isolates the AD590 from

supply variations while maintaining a reasonable voltage (~7 V)

across it. Capacitor C1 is often needed to filter extraneous noise

from remote sensors. R

is determined by the β of the power

transistor and the current requirements of the load.

Figure 22. Simple Temperature Control Circuit

The voltage compliance and the reverse blocking characteristic

of the AD590 allow it to be powered directly from 5 V CMOS

logic. This permits easy multiplexing, switching, or pulsing for

minimum internal heat dissipation. In Figure 23, any AD590

connected to a logic high passes a signal current through the

current measuring circuitry, while those connected to a logic

zero pass insignificant current. The outputs used to drive the

AD590s can be employed for other purposes, but the additional

capacitance due to the AD590 should be taken into account.

Figure 23. AD590 Driven from CMOS Logic

00533-018

30pF

V+

4mA = 17°C

12mA = 25°C

20mA = 33°C

–

AD581

OUT

5kΩ

10Ω

10kΩ

12.7kΩ

35.7kΩ

5kΩ 500Ω

AD590

OP177

–

0.01µF

V–

00533-019

AD790

–

10kΩ

SET

V–

V+

AD590

–

AD581

OUT

HEATING

ELEMENTS

GND

10V

00533-021

CMOS

GATES

AD590

1kΩ (0.1%)

–

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P17

AD590LF

Mfr. #:

Buy AD590LF

Manufacturer:

Analog Devices Inc.

Description:

Board Mount Temperature Sensors 2-Terminal IC Temp TRANSDUCER

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AD590LF

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