AD590
VOLTAGE AND THERMAL ENVIRONMENT EFFECTS
1.6
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.
0.8
0.8°C MAX
0
0.8°C
MAX
0.8°C
MAX
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 10).
–0.8
–1.6
–55
150
TEMPERATURE (°C)
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.
Figure 11. Nonlinearity
Figure 12 shows a circuit in which the nonlinearity is the major
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.
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 14 is a
model of the AD590 that demonstrates these characteristics.
T
θ
T
θ
CA
J
JC
C
+
–
15V
P
T
A
C
C
C
CH
R1
R2
2kΩ
5kΩ
35.7kΩ
27kΩ
97.6kΩ
AD581
Figure 14. Thermal Circuit Model
30pF
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
100mV/°C
= 100mV/°C
AD707A
V
T
AD590
V–
Figure 12. 2-Temperature Trim
TJ − TA = P(θJC + θCA)
(1)
2
0
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.
–2
–55
0
100
150
TEMPERATURE (°C)
Figure 13. Typical 2-Trim Accuracy
Rev. D | Page 8 of 16
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