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Applying the AD790 0.1µF

0.1µF

0.1µF

1 510Ω

1 +IN

+IN

8

2

8

2

5

AD790

5

AD790 –IN

10 mV reference level that is compared to the sense voltage. The minus supply current is proportional to absolute temperature 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. ILIMIT = 10 mV/RSENSE RSENSE = rho (trace length/trace width)

+5V

+5V + 12V

OUT

7 6

3

7

OUT

6

3

–IN

4

4

0.1µF

+VS = +12V, –VS = 0V

–15V

+5V

VLOGIC = +5V

0.1µF

+VS = +5V, –VS = –15V VLOGIC = +5V

rho = resistance of a unit square of trace

1 +IN

–IN

8

2

3

5

AD790

7

OUT

+VS

6 4 0.1µF

L O A D

– 5V +VS = +5V, –VS = –5V, VLOGIC = +5V

Figure 15. Typical Power Supply Connections (N, Q Package Pinout)

+ 5V

1 PC BOARD TRACE

5

AD790

The wide differential input range of the AD790 makes it suitable for monitoring large amplitude signals. The simple overvoltage detection circuit shown in Figure 16 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 differential input voltage across the inputs. +5V

510Ω 8

2

Window Comparator for Overvoltage Detection

0.1µF

0.1µF

OUTPUT

7 6

3 4

RSENSE

2.7ΩΩ

≈ 10mV/100mA

0.1µF

+15V

1 +7.5V

SIGN 1 = HIGH 0 = LOW

8

3

5

AD790

Precision Full-Wave Rectifier

7

The high speed and precision of the AD790 make it suitable for use in the wide dynamic range full-wave rectifier shown in Figure 18. This circuit is capable of rectifying low level signals as small as a few mV or as high as 10 V. Input resolution, propagation 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.

6

2 4

OVERRANGE = 1

7432

–15V VIN

Figure 17. Ground Referred Overload Detector Circuit (N, Q Package Pinout)

510Ω

0.1µF +15V

0.1µF

+5V 0.1µF

1 510Ω

8

3

10k Ω

5

AD790 –7.5V

+15V

7

0.1µF

6

2

10k Ω

4

VIN –15V

20k Ω +15V

0.1µF

Figure 16. Overvoltage Detector (N, Q Package Pinout)

4

6 0.1µF

–15V 1

510Ω

8

3

Single Supply Ground Referred Overload Detector

5 6

2

FET SWITCHES THE GAIN FROM +1 TO –1

7

AD790

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 16. The comparator 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

REV. B

AD711 3

0.1µF

+5V

0.1µF

7

2

4

NMOS FET (RON < 20 Ω)

–15V 0.1µF

Figure 18. Precision Full-Wave Rectifier (N, Q Package Pinout)

–7–

VOUT


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