OPA188_13 Datasheet, PDF (17/33 Pages) Texas Instruments – Precision, Low-Noise, Rail-to-Rail Output,36-V, Zero-Drift Operational Amplifiers

OPA188
www.ti.com
SBOS642A – MARCH 2013 – REVISED MARCH 2013
GENERAL LAYOUT GUIDELINES
For best operational performance of the device, good printed circuit board (PCB) layout practices are
recommended. Including:
• Low-ESR, 0.1-µF ceramic bypass capacitors should be connected between each supply pin and ground,
placed as close to the device as possible. A single bypass capacitor from V+ to ground is applicable to
single-supply applications.
• In order to reduce parasitic coupling, run the input traces as far away from the supply lines as possible.
• A ground plane helps distribute heat and reduces EMI noise pickup.
• Place the external components as close to the device as possible. This configuration prevents parasitic
errors (such as the Seebeck effect) from occurring.
• Consider a driven, low-impedance guard ring around the critical traces. A guard ring can significantly
reduce leakage currents from nearby traces that are at different potentials.
PHASE-REVERSAL PROTECTION
The OPA188 has an internal phase-reversal protection. Many op amps exhibit a phase reversal when the input is
driven beyond its linear common-mode range. This condition is most often encountered in noninverting circuits
when the input is driven beyond the specified common-mode voltage range, causing the output to reverse into
the opposite rail. The OPA188 input prevents phase reversal with excessive common-mode voltage. Instead, the
output limits into the appropriate rail. This performance is shown in Figure 40.
+18 V
Device
-18 V
37 VPP
Sine Wave
(±18.5 V)
V_IN
V_OUT
Time (100 ms/div)
Figure 40. No Phase Reversal
INPUT BIAS CURRENT CLOCK FEEDTHROUGH
Zero-drift amplifiers, such as the OPA188, use switching on their inputs to correct for the intrinsic offset and drift
of the amplifier. Charge injection from the integrated switches on the inputs can introduce very short transients in
the input bias current of the amplifier. The extremely short duration of these pulses prevents them from being
amplified, however they may be coupled to the output of the amplifier through the feedback network. The most
effective method to prevent transients in the input bias current from producing additional noise at the amplifier
output is to use a low-pass filter such as an RC network.
INTERNAL OFFSET CORRECTION
The OPA188 op amp uses an auto-calibration technique with a time-continuous 750-kHz op amp in the signal
path. This amplifier is zero-corrected every 3 μs using a proprietary technique. Upon power-up, the amplifier
requires approximately 100 μs to achieve the specified V_OS accuracy. This design has no aliasing or flicker noise.
Copyright © 2013, Texas Instruments Incorporated
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