OPA1662-Q1_16 Datasheet, PDF (17/33 Pages) Texas Instruments – Operational Amplifier

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OPA1662-Q1
SLOS805C – JULY 2012 – REVISED AUGUST 2016
Op amp distortion can be considered an internal error source that can be referred to the input. Figure 47 shows a
circuit that causes the op amp distortion to be gained up (see the table in Figure 47 for the distortion gain factor
for various signal gains). The addition of R₃ to the otherwise standard noninverting amplifier configuration alters
the feedback factor or noise gain of the circuit. The closed-loop gain is unchanged, but the feedback available for
error correction is reduced by the distortion gain factor, thus extending the resolution by the same amount. The
input signal and load applied to the op amp are the same as with conventional feedback without R₃. The value of
R₃ must be kept small to minimize its effect on the distortion measurements.
The validity of this technique can be verified by duplicating measurements at high gain or high frequency where
the distortion is within the measurement capability of the test equipment. Measurements for this data sheet were
made with an Audio Precision System Two distortion and noise analyzer, which greatly simplifies such repetitive
measurements. The measurement technique can, however, be performed with manual distortion measurement
instruments.
8.3.6 Capacitive Loads
The dynamic characteristics of the OPA1662-Q1 have been optimized for commonly encountered gains, loads,
and operating conditions. The combination of low closed-loop gain and high capacitive loads decreases the
phase margin of the amplifier and can lead to gain peaking or oscillations. As a result, heavier capacitive loads
must be isolated from the output. The simplest way to achieve this isolation is to add a small resistor (R_S equal to
50 Ω, for example) in series with the output.
This small series resistor also prevents excess power dissipation if the output of the device becomes shorted.
Figure 25 illustrates a graph of Small-Signal Overshoot vs Capacitive Load for several values of R_S. Also see
Applications Bulletin: Feedback Plots Define Op Amp AC Performance for details of analysis techniques and
application circuits.
R₁
R₂
Signal Gain = 1+ ^R2
R₁
Distortion Gain = 1+ ^R2
R₁ II R₃
R₃
OPA1662-Q1
Generator
Output
Analyzer
Input
V_O = 3 V_RMS
SIGNAL DISTORTION
GAIN
GAIN
R₁
R₂
R₃
+1
101
Â¥
1 kW 10 W
-1
101
4.99 kW 4.99 kW 49.9 W
+10
110
549 W 4.99 kW 49.9 W
Audio Precision
System Two⁽¹⁾
with PC Controller
Load
(1) For measurement bandwidth, see Figure 7 through Figure 12.
Figure 47. Distortion Test Circuit
8.3.7 Electrical Overstress
Designers often ask questions about the capability of an operational amplifier to withstand electrical overstress.
These questions tend to focus on the device inputs, but may involve the supply voltage pins or even the output
pin. Each of these different pin functions have electrical stress limits determined by the voltage breakdown
characteristics of the particular semiconductor fabrication process and specific circuits connected to the pin.
Additionally, internal electrostatic discharge (ESD) protection is built into these circuits to protect them from
accidental ESD events both before and during product assembly.
It is helpful to have a good understanding of this basic ESD circuitry and its relevance to an electrical overstress
event. Figure 48 illustrates the ESD circuits contained in the OPA1662-Q1 (indicated by the dashed line area).
The ESD protection circuitry involves several current-steering diodes connected from the input and output pins
and routed back to the internal power-supply lines, where they meet at an absorption device internal to the
operational amplifier. This protection circuitry is intended to remain inactive during normal circuit operation.
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