op497fy Analog Devices, Inc., op497fy Datasheet - Page 7

• Manufacturer Part Number: op497fy
• Description: Precision Picoampere Input Current Quad Operational Amplifier
• Manufacturer: Analog Devices, Inc.

APPLICATIONS INFORMATION
Extremely low bias current over the full military temperature range
makes the OP497 attractive for use in sample-and-hold amplifiers,
peak detectors, and log amplifiers that must operate over a wide
temperature range. Balancing input resistances is not necessary
with the OP497. Offset voltage and TCV
minimally by high source resistance, even when unbalanced.
The input pins of the OP497 are protected against large differen-
tial voltage by back-to-back diodes and current-limiting resistors.
Common-mode voltages at the inputs are not restricted, and may
vary over the full range of the supply voltages used.
The OP497 requires very little operating headroom about the
supply rails, and is specified for operation with supplies as low
as ± 2 V. Typically, the common-mode range extends to within
1 V of either rail. The output typically swings to within 1 V of
the rails when using a 10 kΩ load.
AC PERFORMANCE
The OP497’s ac characteristics are highly stable over its full
operating temperature range. Unity-gain small-signal response is
shown in Figure 1. Extremely tolerant of capacitive loading on
the output, the OP497 displays excellent response even with
1000 pF loads (Figure 2).
100
100
0%
0%
10
90
10
90
20mV
20MV
5 s
5 s
OS
are degraded only
GUARDING AND SHIELDING
To maintain the extremely high input impedances of the OP497,
care must be taken in circuit board layout and manufacturing.
Board surfaces must be kept scrupulously clean and free of mois-
ture. Conformal coating is recommended to provide a humidity
barrier. Even a clean PC board can have 100 pA of leakage currents
between adjacent traces, so guard rings should be used around
the inputs. Guard traces are operated at a voltage close to that
on the inputs, as shown in Figure 4, so that leakage currents
become minimal. In noninverting applications, the guard ring
should be connected to the common-mode voltage at the invert-
ing input. In inverting applications, both inputs remain at ground,
so the guard trace should be grounded. Guard traces should be
on both sides of the circuit board.
UNITY GAIN FOLLOWER
INVERTING AMPLIFIER
100
0%
90
10
–
OP497
+
1/4
OP497
–
+
2V
1/4
50 s
NONINVERTING AMPLIFIER
B
8
BOTTOM VIEW
–
+
OP497
1/4
MINI-DIP
OP497
1
A