AD590

Data Sheet

Rev. G | Page 6 of 16

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.

Figure 6. Metallization Diagram

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.

Figure 8 shows the typical V–I characteristic of the circuit at

25°C and the temperature extremes.

Figure 7. Schematic Diagram

Figure 8. V–I Plot

1725µM

1090µM

V–

V+

Q1

Q2

R2

1040Ω

Q5

Q3

Q4

C1

26pF

Q6

Q7

Q12

R4

11kΩ

Q8

Q10

Q9

CHIP

SUBSTRATE

Q11

1

1

8

R5

146Ω

R6

820Ω

R1

260Ω

+

–

R3

5kΩ

01

2

+150°C

423

298

218

+25°C

–55°C

34

SUPPLY VOLTAGE (V)

56

30