OPA2188 Datasheet, PDF (16/26 Pages) Texas Instruments – 0.03-μV/°C Drift, Low-Noise, Rail-to-Rail Output

OPA2188
SBOS525B – AUGUST 2011 – REVISED SEPTEMBER 2012
www.ti.com
GENERAL LAYOUT GUIDELINES
For best operational performance of the device, good printed circuit board (PCB) layout practices are
recommended. Low-loss, 0.1-µF 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.
PHASE-REVERSAL PROTECTION
The OPA2188 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 OPA2188 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
CAPACITIVE LOAD AND STABILITY
The dynamic characteristics of the OPA2188 have been optimized for a range of common 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 (for example, R_OUT equal to 50 Ω) in
series with the output. Figure 41 and Figure 42 illustrate graphs of small-signal overshoot versus capacitive load
for several values of R_OUT. Also, refer to the Applications Report, Feedback Plots Define Op Amp AC
Performance (SBOA015), available for download from the TI website, for details of analysis techniques and
application circuits.
40
R_L = 10 kW
35
R_OUT = 0 W
30
R_OUT = 25 W
25
R_OUT = 50 W
20
15
G = +1
+18 V
10
Device
ROUT
-18 V
RL
CL
5
0
0 100 200 300 400 500 600 700 800 900 1000
Capacitive Load (pF)
Figure 41. Small-Signal Overshoot versus
Capacitive Load (100-mV Output Step)
40
R_OUT = 0 W
35
R_OUT = 25 W
30
R_OUT = 50 W
25
20
15
10
5
R_L = 10 kW
0
0 100 200
300
400
500
G = -1 ^RI ^{= 10 kW R}F ^{= 10 kW}
+18 V
Device
-18 V
ROUT
CL
600 700 800 900 1000
Capacitive Load (pF)
Figure 42. Small-Signal Overshoot versus
Capacitive Load (100-mV Output Step)
16
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