AD590
PRODUCT DESCRIPTION
The AD590 is a 2-terminal temperature-to-voltage transducer. It
is available in a variety of accuracy grades and packages. When
using the AD590 in die form, the chip substrate must be kept
electrically isolated (floating) for correct circuit operation.
1725µM
Q1
Q2
Data Sheet
25°C and the temperature extremes.
+
R1
260Ω
Q5
R2
1040Ω
Q3
C1
26pF
Q12
Q8
Q4
Q6
V–
1090µM
Q7
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V+
CHIP
SUBSTRATE
Q9
8
R3
5kΩ
Q10
R4
11kΩ
Figure 6. Metallization Diagram
Q11
00533-004
I
OUT
(µA)
The AD590 uses a fundamental property of the silicon
transistors from which it is made to realize its temperature
proportional characteristic: if two identical transistors are
operated at a constant ratio of collector current densities, r,
then the difference in their base-emitter voltage is (kT/q)(In r).
Because both k (Boltzman’s constant) and q (the charge of an
electron) are constant, the resulting voltage is directly pro-
portional to absolute temperature (PTAT). (For a more detailed
description, see M.P. Timko, “A Two-Terminal IC Temperature
Transducer,” IEEE J. Solid State Circuits, Vol. SC-11, p. 784-788,
Dec. 1976. Understanding the Specifications–AD590.)
In the AD590, this PTAT voltage is converted to a PTAT current
by low temperature coefficient thin-film resistors. The total
current of the device is then forced to be a multiple of this
PTAT current. Figure 7 is the schematic diagram of the AD590.
In this figure, Q8 and Q11 are the transistors that produce the
PTAT voltage. R5 and R6 convert the voltage to current. Q10,
whose collector current tracks the collector currents in Q9 and
Q11, supplies all the bias and substrate leakage current for the
rest of the circuit, forcing the total current to be PTAT. R5 and
R6 are laser-trimmed on the wafer to calibrate the device at 25°C.
R6
820Ω
–
R5 1
146Ω
1
Figure 7. Schematic Diagram
423
+150°C
298
+25°C
–55°C
218
0
1
2
3
4
5
SUPPLY VOLTAGE (V)
6
30
Figure 8. V–I Plot
Rev. G | Page 6 of 16
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