10

100

1000

10000

0.1

1

10

100

1000

Capacitive Load (nF)

45°Phase Margin

60°Phase Margin

C002

0

AOL

1/

20

40

60

80

10

100

1k

10k

100k

1M

100

120

10M

100M

Frequency (Hz)

20 dB

ROC

dec

40 dB

1 dec

z

ISO

LOAD

1

f

2

R

C

Œ

u

u

u

p

ISO

o

LOAD

1

f

2

R

R

C

Œ

u

u

u

21

TLV171, TLV2171, TLV4171

www.ti.com

SBOS783 – SEPTEMBER 2016

Product Folder Links: TLV171 TLV2171 TLV4171

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Copyright © 2016, Texas Instruments Incorporated

Typical Application (continued)

Figure 31. Unity-Gain Amplifier With RISO Compensation

ROC stability analysis is typically simulated. The validity of the analysis depends on multiple factors, especially

the accurate modeling of RO. In addition to simulating the ROC, a robust stability analysis includes a

measurement of overshoot percentage and ac gain peaking of the circuit using a function generator,

oscilloscope, and gain and phase analyzer. Phase margin is then calculated from these measurements. Table 2

shows the overshoot percentage and ac gain peaking that correspond to phase margins of 45° and 60°. For

more details on this design and other alternative devices that can be used in place of the TLV171, see the

Precision Design, Capacitive Load Drive Solution Using an Isolation Resistor.

Table 2. Phase Margin versus Overshoot and AC Gain

Peaking

PHASE

MARGIN

OVERSHOOT

AC GAIN PEAKING

45°

23.3%

2.35 dB

60°

8.8%

0.28 dB

8.2.3 Application Curve

Using the described methodology, the values of RISO that yield phase margins of 45º and 60º for various

capacitive loads were determined. The results are shown in Figure 32.

Figure 32. Isolation Resistor Required for Various Capacitive Loads to Achieve a Target Phase Margin