AD795KN Analog Devices, AD795KN Datasheet - Page 12

• Manufacturer Part Number: AD795KN
• Description: Low Power/ Low Noise Precision FET Op Amp
• Manufacturer: Analog Devices

AD795
INPUT PROTECTION
The AD795 safely handles any input voltage within the supply
voltage range. Some applications may subject the input
terminals to voltages beyond the supply voltages—in these
cases, the following guidelines should be used to maintain the
AD795’s functionality and performance.
If the inputs are driven more than a 0.5 V below the minus sup-
ply, milliamp level currents can be produced through the input
terminals. That current should be limited to 10 mA for “tran-
sient” overloads (less than 1 second) and 1 mA for continuous
overloads, this can be accomplished with a protection resistor in
the input terminal (as shown in Figures 40 and 41). The pro-
tection resistor’s Johnson noise will add to the amplifier’s input
voltage noise and impact the frequency response.
Driving the input terminals above the positive supply will cause
the input current to increase and limit at 40 A. This condition
is maintained until 15 volts above the positive supply—any
input voltage within this range does not harm the amplifier.
Input voltage above this range causes destructive breakdown
and should be avoided.
Figure 40. Inverter with Input Current Limit
SOURCE
R
P
R
F
3
2
AD795
C
F
6
–12–
Figure 42 is a schematic of the AD795 as an inverter with an
input voltage clamp. Bootstrapping the clamp diodes at the
inverting input minimizes the voltage across the clamps and
keeps the leakage due to the diodes low. Low leakage diodes
(less than 1 pA), such as the FD333s should be used, and
should be shielded from light to keep photocurrents from being
generated. Even with these precautions, the diodes will mea-
surably increase the input current and capacitance.
In order to achieve the low input bias currents of the AD795, it
is not possible to use the same on-chip protection as used in
other Analog Devices op amps. This makes the AD795
sensitive to handling and precautions should be taken to
minimize ESD exposure whenever possible.
Figure 41. Follower with Input Current Limit
Figure 42. Input Voltage Clamp with Diodes
SOURCE
SOURCE
PROTECT DIODES
(LOW LEAKAGE)
R
P
2
3
3
2
AD795
AD795
R
F
6
6
REV. A