V

IN

V

OUT

V+

R

S

10

to

20

W

W

R

L

C

L

Device

15

TLV314, TLV2314, TLV4314

www.ti.com

SBOS754A – MARCH 2016 – REVISED MARCH 2016

Product Folder Links: TLV314 TLV2314 TLV4314

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Copyright © 2016, Texas Instruments Incorporated

Feature Description (continued)

8.3.5 Capacitive Load and Stability

The TLV314 is designed to be used in applications where driving a capacitive load is required. As with all

operational amplifiers, there may be specific instances where the TLV314 can become unstable. The particular

operational amplifier circuit configuration, layout, gain, and output loading are some of the factors to consider

when establishing whether or not an amplifier is stable in operation. An operational amplifier in the unity-gain

(1 V/V) buffer configuration that drives a capacitive load exhibits a greater tendency to be unstable than an

amplifier operated at a higher noise gain. The capacitive load, in conjunction with the operational amplifier output

resistance, creates a pole within the feedback loop that degrades the phase margin. The degradation of the

phase margin increases when capacitive loading increases. When operating in the unity-gain configuration, the

TLV314 remains stable with a pure capacitive load up to approximately 1 nF. The equivalent series resistance

(ESR) of some very large capacitors (CL greater than 1 μF) is sufficient to alter the phase characteristics in the

feedback loop such that the amplifier remains stable. Increasing the amplifier closed-loop gain allows the

amplifier to drive increasingly larger capacitance. This increased capability is evident when measuring the

overshoot response of the amplifier at higher voltage gains; see Figure 8.

One technique for increasing the capacitive load drive capability of the amplifier operating in a unity-gain

configuration is to insert a small resistor (typically 10

Ω to 20 Ω) in series with the output, as shown in Figure 14.

This resistor significantly reduces the overshoot and ringing associated with large capacitive loads. One possible

problem with this technique, however, is that a voltage divider is created with the added series resistor and any

resistor connected in parallel with the capacitive load. The voltage divider introduces a gain error at the output

that reduces the output swing.

Figure 14. Improving Capacitive Load Drive

8.3.6 EMI Susceptibility and Input Filtering

Operational amplifiers vary with regard to the susceptibility of the device to electromagnetic interference (EMI). If

conducted EMI enters the operational amplifier, the dc offset observed at the amplifier output can shift from its

nominal value when EMI is present. This shift is a result of signal rectification associated with the internal

semiconductor junctions. Although all operational amplifier pin functions can be affected by EMI, the signal input

pins are likely to be the most susceptible. The TLV314 operational amplifier family incorporates an internal input

low-pass filter that reduces the amplifiers response to EMI. Both common-mode and differential mode filtering

are provided by this filter. The filter is designed for a cutoff frequency of approximately 80 MHz (–3 dB), with a

roll-off of 20 dB per decade.

Texas Instruments has developed the ability to accurately measure and quantify the immunity of an operational

amplifier over a broad frequency spectrum extending from 10 MHz to 6 GHz. The EMI rejection ratio (EMIRR)

metric allows operational amplifiers to be directly compared by the EMI immunity. Figure 13 illustrates the results

of this testing on the TLV314. Detailed information can also be found in application report, EMI Rejection Ratio of

Operational Amplifiers (SBOA128), available for download from www.ti.com.

8.4 Device Functional Modes

The TLV314 family has a single functional mode. These devices are powered on as long as the power-supply

voltage is between 1.8 V (±0.9 V) and 5.5 V (±2.75 V).