W

W

W

R =

I

10 kW

R

OUT

C

L

R

F

= 10 kW

18 V

-18 V

W

W

W

18 V

-18 V

R

OUT

C

L

R

L

19

TLV170, TLV2170, TLV4170

www.ti.com

SBOS782A – NOVEMBER 2016 – REVISED MAY 2018

Product Folder Links: TLV170 TLV2170 TLV4170

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Copyright © 2016–2018, Texas Instruments Incorporated

Feature Description (continued)

Another common question involves what happens to the amplifier if an input signal is applied to the input when

the power supplies (V+ or V–) are at 0 V. Again, this question depends on the supply characteristic when at 0 V,

or at a level below the input signal amplitude. If the supplies appear as high impedance, then the input source

supplies the op amp current through the current-steering diodes. This state is not a normal bias condition; most

likely, the amplifier does not operate normally. If the supplies are low impedance, then the current through the

steering diodes can become quite high. The current level depends on the ability of the input source to deliver

current, and any resistance in the input path.

If there is any uncertainty about the ability of the supply to absorb this current, add external Zener diodes to the

supply pins; see Figure 27. Select the Zener voltage so that the diode does not turn on during normal operation.

However, the Zener voltage must be low enough so that the Zener diode conducts if the supply pin begins to rise

above the safe-operating, supply-voltage level.

The TLVx170 input pins are protected from excessive differential voltage with back-to-back diodes; see

Figure 27. In most circuit applications, the input protection circuitry has no effect. However, in low-gain or G = 1

circuits, fast-ramping input signals can forward-bias these diodes because the output of the amplifier cannot

respond rapidly enough to the input ramp. If the input signal is fast enough to create this forward-bias condition,

limit the input signal current to 10 mA or less. If the input signal current is not inherently limited, an input series

resistor can be used to limit the input signal current. This input series resistor degrades the low-noise

performance of the TLVx170. Figure 27 illustrates an example configuration that implements a current-limiting

feedback resistor.

7.3.4 Capacitive Load and Stability

The dynamic characteristics of the TLVx170 are optimized for 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, ROUT equal to 50 Ω) in series with the output.

Figure 28 and Figure 29 show graphs of small-signal overshoot versus capacitive load for several values of

ROUT. Also, see the Feedback Plots Define Op Amp AC Performance application report for details of analysis

techniques and application circuits.

100-mV output step, RL = 10 kΩ, G = +1

Figure 28. Small-Signal Overshoot vs Capacitive Load

100-mV output step, RL = 10 kΩ, G = –1

Figure 29. Small-Signal Overshoot vs Capacitive Load