AD590
NONLINEARITY
Nonlinearity as it applies to the AD590 is the maximum
deviation of current over temperature from a best-fit straight
line. The nonlinearity of the AD590 over the −55°C to +150°C
range is superior to all conventional electrical temperature
sensors such as thermocouples, RTDs, and thermistors. Figure 12
shows the nonlinearity of the typical AD590K from Figure 11.
1.6
2
TEMPERATURE (°C)
Data Sheet
0
ABSOLUTE ERROR (°C)
0.8
0.8°C MAX
0
0.8°C
MAX
–0.8
00533-009
–2
–55
0
TEMPERATURE (°C)
100
150
Figure 14. Typical 2-Trim Accuracy
0.8°C
MAX
VOLTAGE AND THERMAL ENVIRONMENT EFFECTS
The power supply rejection specifications show the maximum
expected change in output current vs. input voltage changes.
The insensitivity of the output to input voltage allows the use of
unregulated supplies. It also means that hundreds of ohms of
resistance (such as a CMOS multiplexer) can be tolerated in
series with the device.
It is important to note that using a supply voltage other than 5 V
does not change the PTAT nature of the AD590. In other words,
this change is equivalent to a calibration error and can be
removed by the scale factor trim (see Figure 11).
The AD590 specifications are guaranteed for use in a low
thermal resistance environment with 5 V across the sensor.
Large changes in the thermal resistance of the sensor’s environment
change the amount of self-heating and result in changes in the
output, which are predictable but not necessarily desirable.
The thermal environment in which the AD590 is used
determines two important characteristics: the effect of self-
heating and the response of the sensor with time. Figure 15 is a
model of the AD590 that demonstrates these characteristics.
T
J
θ
JC
T
C
θ
CA
+
T
A
–1.6
–55
TEMPERATURE (°C)
150
Figure 12. Nonlinearity
contributor to error over temperature. The circuit is trimmed
by adjusting R1 for a 0 V output with the AD590 at 0°C. R2 is
then adjusted for 10 V output with the sensor at 100°C. Other
pairs of temperatures can be used with this procedure as long as
they are measured accurately by a reference sensor. Note that
for 15 V output (150°C), the V+ of the op amp must be greater
than 17 V. Also, note that V− should be at least −4 V; if V− is
ground, there is no voltage applied across the device.
15V
35.7kΩ
R1
2kΩ
97.6kΩ
R2
5kΩ
30pF
27kΩ
AD581
OP177
100mV/°C
V
T
= 100mV/°C
00533-010
–
V–
Figure 13. 2-Temperature Trim
Figure 15. Thermal Circuit Model
Rev. G | Page 8 of 16
00533-012
AD590
P
C
CH
C
C
00533-011
AD [ ANALOG DEVICES ]
