LM158-N, LM258-N, LM2904-N, LM358-N

SNOSBT3I – JANUARY 2000 – REVISED DECEMBER 2014

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8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

The LM158 family bring performance, economy, and ease-of-use to a wide variety of op-amp applications.

8.2 Typical Applications

8.2.1 Noninverting DC Gain

Figure 17 shows a high input impedance non-inverting circuit. This circuit gives a closed-loop gain equal to the

ratio of the sum of R1 and R2 to R1 and a closed-loop 3 dB bandwidth equal to the amplifier unity-gain frequency

divided by the closed-loop gain. This design has the benefit of a very high input impedance, which is equal to the

differential input impedance multiplied by loop gain. (Open loop gain/Closed loop gain.) In DC coupled

applications, input impedance is not as important as input current and its voltage drop across the source

resistance. Note that the amplifier output will go into saturation if the input is allowed to float. This may be

important if the amplifier must be switched from source to source.

Figure 17. Non-Inverting DC Gain (0-V Output)

8.2.1.1 Design Requirements

For this example application, the supply voltage is +5V, and 100x±5% of noninverting gain is necessary. Signal

input impedance is approx 10k

Ω.

8.2.1.2 Detailed Design Procedure

Using the equation for a non-inverting amplifier configuration ; G = 1+ R2/R1, set R1 to 10k

Ω, and R2 to 99x the

value of R1, which would be 990k

Ω. Replacing the 990kΩ with a 1MΩ will result in a gain of 101, which is within

the desired gain tolerance.

The gain-frequency characteristic of the amplifier and its feedback network must be such that oscillation does not

occur. To meet this condition, the phase shift through amplifier and feedback network must never exceed 180°

for any frequency where the gain of the amplifier and its feedback network is greater than unity. In practical

applications, the phase shift should not approach 180° since this is the situation of conditional stability. Obviously

the most critical case occurs when the attenuation of the feedback network is zero.

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