Datasheet

LMV301

SNOS968A –MAY 2004–REVISED MAY 2013

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(7)

the feedback capacitor should be:

(8)

Note that these capacitor values are usually significantly smaller than those given by the older, more

conservative formula:

(9)

consists of the amplifier's input capacitance plus any stray capacitance from the circuit board and socket. C

compensates for the pole caused by C

and the feedback resistors.

Figure 35. General Operational Amplifier Circuit

Using the smaller capacitor will give much higher bandwidth with little degradation of transient response. It may

be necessary in any of the above cases to use a somewhat larger feedback capacitor to allow for unexpected

stray capacitance, or to tolerate additional phase shifts in the loop, or excessive capacitive load, or to decrease

the noise or bandwidth, or simply because the particular circuit implementation needs more feedback

capacitance to be sufficiently stable. For example, a printed circuit board's stray capacitance may be larger or

smaller than the breadboard's, so the actual optimum value for C

may be different from the one estimated using

the breadboard. In most cases, the values of C

should be checked on the actual circuit, starting with the

computed value.

Capacitive Load Tolerance

Like many other op amps, the LMV301 may oscillate when its applied load appears capacitive. The threshold of

oscillation varies both with load and circuit gain. The configuration most sensitive to oscillation is a unity gain

follower. The load capacitance interacts with the op amp’s output resistance to create an additional pole. If this

pole frequency is sufficiently low, it will degrade the op amp's phase margin so that the amplifier is no longer

stable. As shown in Figure 36, the addition of a small resistor (50Ω to 100Ω) in series with the op amp's output,

and a capacitor (5pF to 10pF) from inverting input to output pins, returns the phase margin to a safe value

without interfering with lower frequency circuit operation. Thus, larger values of capacitance can be tolerated

without oscillation. Note that in all cases, the output will ring heavily when the load capacitance is near the

threshold for oscillation.

Product Folder Links: LMV301