Datasheet OP297 (Analog Devices) - 9

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OP297 APPLICATIONS INFORMATION
Extremely low bias current over a wide temperature range makes the OP297 attractive for use in sample-and-hold amplifiers, peak detectors, and log amplifiers that must operate
100
over a wide temperature range. Balancing input resistances is
90
unnecessary with the OP297. Offset voltage and TCVOS are degraded only minimally by high source resistance, even when unbalanced. The input pins of the OP297 are protected against large differen- tial voltage by back-to-back diodes and current-limiting resistors.
10 0%
Common-mode voltages at the inputs are not restricted and can 8 vary over the full range of the supply voltages used.
20mV 5µs
-02 00 03 The OP297 requires very little operating headroom about the 0 Figure 28. Large Signal Transient Response (AVCL = +1) supply rails and is specified for operation with supplies as low as 2 V. Typically, the common-mode range extends to within 1 V
GUARDING AND SHIELDING
of either rail. The output typically swings to within 1 V of the To maintain the extremely high input impedances of the OP297, rails when using a 10 kΩ load. care is taken in circuit board layout and manufacturing. Board
AC PERFORMANCE
surfaces must be kept scrupulously clean and free of moisture. Conformal coating is recommended to provide a humidity The ac characteristics of the OP297 are highly stable over its full barrier. Even a clean PCB can have 100 pA of leakage currents operating temperature range. Unity gain small signal response is between adjacent traces, therefore guard rings should be used shown in Figure 26. Extremely tolerant of capacitive loading on around the inputs. Guard traces operate at a voltage close to that the output, the OP297 displays excellent response with 1000 pF on the inputs, as shown in Figure 29, to minimize leakage loads (see Figure 27). currents. In noninverting applications, the guard ring should be connected to the common-mode voltage at the inverting input. In inverting applications, both inputs remain at ground, so the
100
guard trace should be grounded. Guard traces should be placed
90
on both sides of the circuit board.
UNITY-GAIN FOLLOWER NONINVERTING AMPLIFIER 10 – – 10 1/2 1/2 0% OP297 OP297 + + 20mV 5µs
26 0 0- 030 0 Figure 26. Small Signal Transient Response (CL = 100 pF, AVCL = +1)
MINI-DIP INVERTING AMPLIFIER BOTTOM VIEW 8 1 100 90 A – 1/2 B OP297 +
29 0 00- 003 Figure 29. Guard Ring Layout and Considerations
10 0% 20mV 5µs
7 02 0- 30 00 Figure 27. Small Signal Transient Response (CL = 1000 pF, AVCL = +1) Rev. G | Page 9 of 16 Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION PIN CONFIGURATION TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ELECTRICAL CHARACTERISTICS ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE ESD CAUTION TYPICAL PERFORMANCE CHARACTERISTICS APPLICATIONS INFORMATION AC PERFORMANCE GUARDING AND SHIELDING OPEN-LOOP GAIN LINEARITY APPLICATION CIRCUITS PRECISION ABSOLUTE VALUE AMPLIFIER PRECISION CURRENT PUMP PRECISION POSITIVE PEAK DETECTOR SIMPLE BRIDGE CONDITIONING AMPLIFIER NONLINEAR CIRCUITS OUTLINE DIMENSIONS ORDERING GUIDE