AD590 Просмотр технического описания (PDF) - Analog Devices

Номер в каталоге

Компоненты Описание

производитель

AD590

2-Terminal IC Temperature Transducer

Analog Devices 

Data Sheet

EXPLANATION OF TEMPERATURE SENSOR

SPECIFICATIONS

The way in which the AD590 is specified makes it easy to apply

it in a wide variety of applications. It is important to understand

the meaning of the various specifications and the effects of the

supply voltage and thermal environment on accuracy.

The AD590 is a PTAT current regulator. (Note that T (°C) =

T (K) − 273.2. Zero on the Kelvin scale is absolute zero; there is

no lower temperature.) That is, the output current is equal to a

scale factor times the temperature of the sensor in degrees

Kelvin. This scale factor is trimmed to 1 μA/K at the factory, by

adjusting the indicated temperature (that is, the output current)

to agree with the actual temperature. This is done with 5 V

across the device at a temperature within a few degrees of 25°C

(298.2 K). The device is then packaged and tested for accuracy

over temperature.

CALIBRATION ERROR

At final factory test, the difference between the indicated

temperature and the actual temperature is called the calibration

error. Since this is a scale factory error, its contribution to the

total error of the device is PTAT. For example, the effect of the

1°C specified maximum error of the AD590L varies from 0.73°C

at −55°C to 1.42°C at 150°C. Figure 9 shows how an exaggerated

calibration error would vary from the ideal over temperature.

ACTUAL

TRANSFER

FUNCTION

IACTUA L

298.2

CALIBRATION

ERROR

IDEAL

TRANSFER

FUNCTION

298.2

TEMPERATURE (°K)

Figure 9. Calibration Error vs. Temperature

The calibration error is a primary contributor to the maximum

total error in all AD590 grades. However, because it is a scale

factor error, it is particularly easy to trim. Figure 10 shows the

most elementary way of accomplishing this.

To trim this circuit, the temperature of the AD590 is measured

by a reference temperature sensor and R is trimmed so that VT

= 1 mV/K at that temperature. Note that when this error is

trimmed out at one temperature, its effect is zero over the entire

AD590

temperature range. In most applications, there is a current-to-

voltage conversion resistor (or, as with a current input ADC, a

reference) that can be trimmed for scale factor adjustment.

5V +

+

AD590

–

+

R

100Ω VT = 1mV/K

950Ω

–

–

Figure 10. One Temperature Trim

ERROR VS. TEMPERATURE: CALIBRATION ERROR

TRIMMED OUT

Each AD590 is tested for error over the temperature range with

the calibration error trimmed out. This specification could also

be called the variance from PTAT, because it is the maximum

difference between the actual current over temperature and a

PTAT multiplication of the actual current at 25°C. This error

consists of a slope error and some curvature, mostly at the

temperature extremes. Figure 11 shows a typical AD590K

temperature curve before and after calibration error trimming.

2

BEFORE

CALIBRATION

TRIM

CALIBRATION

ERROR

0

AFTER

CALIBRATION

TRIM

–2

–55

150

TEMPERATURE (°C)

Figure 11. Effect to Scale Factor Trim on Accuracy

ERROR VS. TEMPERATURE: NO USER TRIMS

Using the AD590 by simply measuring the current, the total

error is the variance from PTAT, described above, plus the effect

of the calibration error over temperature. For example, the

AD590L maximum total error varies from 2.33°C at −55°C to

3.02°C at 150°C. For simplicity, only the large figure is shown

on the specification page.

Rev. G | Page 7 of 16

Share Link: