OPAX170 datasheet(21/60 Pages) TI2

21 / 60 page

100p

200p

300p

400p

500p

Capacitive Load (F)

RO = 25

RO = 50

C013

G = -1

OUT = 0

OUT = 25

OUT = 50

RI = 1 k

VIN = 100mV

+ 18 V

± 18 V

OPA172

RF = 1 k

ROUT

100p

200p

300p

400p

500p

Capacitive Load (F)

RO = 25

RO = 50

C013

OUT= 0

OUT= 25

OUT= 50

G = +1

VIN = 100mV

+ 18 V

± 18 V

OPA172

ROUT

Time (200 s/div)

C011

OUT

37 VPP

Sine Wave

(±18.5V)

VOUT

+ 18 V

± 18 V

OPA172

OPA172, OPA2172, OPA4172

www.ti.com

SBOS618I – DECEMBER 2013 – REVISED MAY 2018

Product Folder Links: OPA172 OPA2172 OPA4172

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8.3.2 Phase-Reversal Protection

The OPAx172 family has internal phase-reversal protection. Many op amps exhibit a phase reversal when the

input is driven beyond the 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 input of the OPAx172 prevents phase reversal with excessive common-mode

voltage. Instead, the appropriate rail limits the output voltage. This performance is shown in Figure 43.

Figure 43. No Phase Reversal

8.3.3 Capacitive Load and Stability

The dynamic characteristics of the OPAx172 are optimized for commonly-used operating conditions. The

combination of low closed-loop gain and high capacitive loads decreases the phase margin of the amplifier and

may 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, ROUT = 50 Ω) in series with the

output. Figure 44 and Figure 45 show graphs of small-signal overshoot versus capacitive load for several values

of ROUT. Refer to Application Bulletin SBOA015 (AB-028), Feedback Plots Define Op Amp AC Performance,

available for download from www.ti.com, for details of analysis techniques and application circuits.

Figure 44. Small-Signal Overshoot vs Capacitive Load

(100-mV Output Step)

Figure 45. Small-Signal Overshoot vs Capacitive Load

(100-mV Output Step)

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