Applying the AD790
+5V
+ 12V
0.1µF
1
+IN
2
8
5
7
6
4
OUT
–IN
3
4
0.1µF
–15V
0.1µF
1
+IN
2
8
5
7
6
4
0.1µF
– 5V
+V
S
= +5V, –V
S
= –5V, V
LOGIC
= +5V
+V
S
= +5V, –V
S
= –15V
V
LOGIC
= +5V
510Ω
+IN
2
0.1µF
1
8
5
+5V
0.1µF
AD790
–IN
3
AD790
6
7
OUT
+V
S
= +12V, –V
S
= 0V
V
LOGIC
= +5V
+5V
10 mV reference level that is compared to the sense voltage.
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.
I
LIMIT
= 10 mV/R
SENSE
R
SENSE
= rho (trace length/trace width)
rho = resistance of a unit square of trace
+V
S
AD790
–IN
3
OUT
L
O
A
D
+ 5V
0.1µF
Figure 15. Typical Power Supply Connections
(N, Q Package Pinout)
Window Comparator for Overvoltage Detection
1
PC BOARD
TRACE
2
8
5
510Ω
AD790
3
4
6
7
OUTPUT
The wide differential input range of the AD790 makes it suit-
able for monitoring large amplitude signals. The simple over-
voltage 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.
0.1µF
+15V
+5V
0.1µF
R
SENSE
≈
10mV/100mA
2.7Ω
Ω
1
+7.5V
3
8
5
510Ω
SIGN 1 = HIGH
0 = LOW
7
6
4
OVERRANGE = 1
Figure 17. Ground Referred Overload Detector Circuit
(N, Q Package Pinout)
Precision Full-Wave Rectifier
AD790
2
–15V
V
IN
0.1µF
0.1µF
+15V
+5V
0.1µF
1
3
8
5
510Ω
7432
The high speed and precision of the AD790 make it suitable for
use in the wide dynamic range full-wave rectifier shown in Fig-
ure 18. 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.
10k
Ω
+15V
0.1µF
10k
Ω
V
IN
20k
Ω
+15V
0.1µF
+5V
1
3
8
5
0.1µF
–15V
510
Ω
7
6
4
–15V
0.1µF
NMOS
FET
(R
ON
< 20
Ω
)
FET SWITCHES THE GAIN
FROM +1 TO –1
7
AD790
–7.5V
2
4
6
7
2
AD711
3
4
6
0.1µF
V
OUT
–15V
0.1µF
Figure 16. 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 16. 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
AD790
2
Figure 18. Precision Full-Wave Rectifier
(N, Q Package Pinout)
REV. B
–7–
AD [ ANALOG DEVICES ]
