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
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
+V
S
= +12V, –V
S
= 0V
V
LOGIC
= +5V
+5V
AD790
–IN
3
OUT
L
O
A
D
+ 5V
0.1µF
1
Figure 7. Typical Power Supply Connections
(N, Q Package Pinout)
Window Comparator for Overvoltage Detection
PC BOARD
TRACE
510Ω
8
5
2
AD790
3
4
6
7
OUTPUT
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.
0.1µF
+15V
+5V
0.1µF
R
SENSE
≈
10mV/100mA
2.7
Ω
Figure 9. Ground Referred Overload Detector Circuit
(N, Q Package Pinout)
510Ω
8
5
SIGN 1 = HIGH
0 = LOW
7
6
1
+7.5V
3
Precision Full-Wave Rectifier
AD790
2
4
OVERRANGE = 1
–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
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.
10k
Ω
+15V
0.1µF
10k
Ω
V
IN
+15V
0.1µF
+5V
1
3
8
5
0.1µF
–15V
20k
Ω
7
AD790
–7.5V
2
4
6
7
2
AD711
3
4
6
0.1µF
V
OUT
–15V
0.1µF
510
Ω
7
6
Figure 8. Overvoltage Detector
(N, Q Package Pinout)
Single Supply Ground Referred Overload Detector
FET SWITCHES THE GAIN
FROM +1 TO –1
NMOS
FET
(R
ON
< 20
Ω
)
AD790
2
4
–15V
0.1µF
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.
REV. D
–7–
Figure 10. Precision Full-Wave Rectifier
(N, Q Package Pinout)
AD [ ANALOG DEVICES ]
