Datasheet AD790 (Analog Devices) - 7

Applying the AD790 +5V +5V
The minus supply current is proportional to absolute tempera-
+ 12V 0.1µF 0.1µF
ture and compensates for the change in the sense resistance
0.1µF 1
with temperature. The width and length of the PC board trace
1 510
Ω
+IN 2 8 2 8 +IN 5
determine the resistance of the trace and consequently the trip
5 AD790 7 OUT AD790 7 OUT 6 –IN 3
current level.
6 –IN 3 4 4
ILIMIT = 10 mV/RSENSE
0.1µF
RSENSE = rho (trace length/trace width)
+V = +12V, –V = 0V 15V – S S +5V V = +5V +V = +5V, –V = –15V
rho = resistance of a unit square of trace
LOGIC 0.1µF S S V = +5V LOGIC 1 +IN 2 8 +V 5 S AD790 7 OUT 6 –IN 3 4 L 0.1µF O + 5V A 0.1µF – 5V D +V = +5V, –V = –5V, V = +5V S S LOGIC 1 510
Ω Figure 7. Typical Power Supply Connections
PC BOARD 8 TRACE 2
(N, Q Package Pinout)
5 AD790 7 OUTPUT Window Comparator for Overvoltage Detection 6 3
The wide differential input range of the AD790 makes it suitable
4
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
RSENSE 2.7
Ω without the need for special clamp diodes to limit the differen- ≈
10mV/100mA
tial input voltage across the inputs.
+5V 0.1µF 0.1µF +15V
Figure 9. Ground Referred Overload Detector Circuit (N, Q Package Pinout)
1 Precision Full-Wave Rectifier 510
Ω
+7.5V 3 8 SIGN 1 = HIGH
The high speed and precision of the AD790 make it suitable
5 0 = LOW
for use in the wide dynamic range full-wave rectifier shown in
AD790 7
Figure 10. This circuit is capable of rectifying low level signals
6 2
as small as a few mV or as high as 10 V. Input resolution, propaga-
4 OVERRANGE = 1
tion delay and op amp settling will ultimately limit the maximum input frequency for a given accuracy level. Total comparator
7432 –15V
plus switch delay is approximately 100 ns, which limits the
0.1µF VIN
maximum input frequency to 1 MHz for clean rectification.
0.1µF +15V +5V
Ω
0.1µF 10k 1 510
Ω
+15V 0.1µF 3 8 5 AD790 7 10k
Ω
2 7 6 –7.5V 2 VIN AD711 6 4 20k V
Ω
OUT +15V 3 4 0.1µF 0.1µF 0.1µF +5V –15V –15V 0.1µF 1 8 510
Ω
FET SWITCHES THE GAIN 3 5 FROM +1 TO –1
Figure 8. Overvoltage Detector
AD790 7
(N, Q Package Pinout)
6 NMOS 2 FET 4 Single Supply Ground Referred Overload Detector (RON < 20 )
Ω The AD790 is useful as an overload detector for sensitive loads
–15V
that must be powered from a single supply. A simple ground
0.1µF
referenced overload detector is shown in Figure 8. The com- Figure 10. Precision Full-Wave Rectifier parator senses a voltage across a PC board trace and compares (N, Q Package Pinout) 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. E –7–