Data Sheet

AD590

Rev. G | Page 11 of 16

Figure 21 is an example of a current transmitter designed to be

used with 40 V, 1 kΩ systems; it uses its full current range of 4

to 20 mA for a narrow span of measured temperatures. In this

example, the 1 µA/K output of the AD590 is amplified to

1 mA/°C and offset so that 4 mA is equivalent to 17°C and

at an intermediate reference temperature. With a suitable choice

of resistors, any temperature range within the operating limits

of the AD590 can be chosen.

Figure 21. 4 to 20 mA Current Transmitter

Figure 22 is an example of a variable temperature control circuit

calibrated multiturn pot, or a switched resistive divider. Powering

the AD590 from the 10 V reference isolates the AD590 from

supply variations while maintaining a reasonable voltage (~7 V)

across it. Capacitor C1 is often needed to filter extraneous noise

transistor and the current requirements of the load.

Figure 22. Simple Temperature Control Circuit

The voltage compliance and the reverse blocking characteristic

of the AD590 allow it to be powered directly from 5 V CMOS

logic. This permits easy multiplexing, switching, or pulsing for

minimum internal heat dissipation. In Figure 23, any AD590

connected to a logic high passes a signal current through the

current measuring circuitry, while those connected to a logic

zero pass insignificant current. The outputs used to drive the

AD590s can be employed for other purposes, but the additional

capacitance due to the AD590 should be taken into account.

Figure 23. AD590 Driven from CMOS Logic

30pF

V+

4mA = 17°C

12mA = 25°C

20mA = 33°C

–

+

–

+

AD581

5k

Ω

10

Ω

10k

Ω

12.7k

Ω

35.7k

Ω

5k

Ω

500

Ω

AD590

OP177

–

+

V–

AD790

–

+

C1

2

3

4

1

7

10k

Ω

V–

V+

V+

AD590

–

+

AD581

OUT

HEATING

ELEMENTS

GND

10V

5V

CMOS

GATES

AD590

1k

–

+

–

+

–

+

–

+