AD790

REV. D

–7–

AD790

1

2

3

4

5

6

7

8

+IN

–IN

5V

+

OUT

510

Ω

+ 12V

0.1µF

0.1µF

+V

V

AD790

1

2

3

4

5

6

7

8

5V

+

OUT

15V

–

0.1µF

0.1µF

+V

V

+IN

–IN

AD790

1

2

3

4

5

6

7

8

5V

+

OUT

5V

–

0.1µF

0.1µF

+IN

–IN

+V

Figure 7. Typical Power Supply Connections

(N, Q Package Pinout)

Window Comparator for Overvoltage Detection

The wide differential input range of the AD790 makes it suitable

for monitoring large amplitude signals. The simple overvoltage

detection circuit shown in Figure 8 illustrates direct connection

of the input signal to the high impedance inputs of the comparator

without the need for special clamp diodes to limit the differen-

tial

input voltage across the inputs.

510

Ω

OVERRANGE = 1

7432

AD790

1

2

3

4

5

6

7

8

+15V

+5V

–15V

AD790

1

2

3

4

5

6

7

8

+15V

+5V

–15V

510

Ω

0.1µF

0.1µF

0.1µF

0.1µF

0.1µF

0.1µF

SIGN 1 = HIGH

0 = LOW

–7.5V

+7.5V

Figure 8. Overvoltage Detector

(N, Q Package Pinout)

Single Supply Ground Referred Overload Detector

The AD790 is useful as an overload detector for sensitive loads

that must be powered from a single supply. A simple ground

referenced overload detector is shown in Figure 8. The com-

parator senses a voltage across a PC board trace and compares

that to a reference (trip) voltage established by the comparator’s

minus supply current through a 2.7

Ω resistor. This sets up a

10 mV reference level that is compared to the sense voltage.

Applying the

–7–

The minus supply current is proportional to absolute tempera-

ture and compensates for the change in the sense resistance

with temperature. The width and length of the PC board trace

determine the resistance of the trace and consequently the trip

current level.

rho = resistance of a unit square of trace

L

O

A

D

2.7

PC BOARD

TRACE

AD790

1

2

3

4

5

6

7

8

0.1µF

5V

+

OUTPUT

≈ 10mV/100mA

510

Ω

Ω

Figure 9. Ground Referred Overload Detector Circuit

(N, Q Package Pinout)

Precision Full-Wave Rectifier

The high speed and precision of the AD790 make it suitable

for use in the wide dynamic range full-wave rectifier shown in

Figure 10. This circuit is capable of rectifying low level signals

as small as a few mV or as high as 10 V. Input resolution, propaga-

tion delay and op amp settling will ultimately limit the maximum

input frequency for a given accuracy level. Total comparator

plus switch delay is approximately 100 ns, which limits the

maximum input frequency to 1 MHz for clean rectification.

AD711

10k

FET SWITCHES THE GAIN

FROM +1 TO –1

20k

10k

AD790

1

2

3

4

5

6

7

8

+15V

+5V

–15V

2

3

4

6

7

+15V

–15V

NMOS

FET

0.1µF

510

0.1µF

0.1µF

0.1µF

0.1µF

Ω

Ω

Ω

Ω

Ω

Figure 10. Precision Full-Wave Rectifier

(N, Q Package Pinout)