What is LM2902N and How Does it Work?

Many electronic systems need to strengthen, compare, filter, or condition small analog signals before those signals can be used by other circuits. The LM2902N is a low-power quad operational amplifier from Texas Instruments that provides four independent op-amps in one 14-pin package. It can work from a single or split power supply, sense inputs close to ground, and operate across a wide temperature range. This guide explains the LM2902N specifications, internal operation, circuit connections, gain calculations, practical amplifier circuits, and more.

Catalog

LM2902N Op-Amp IC Basic

The LM2902N is a low-power IC containing four independent, high-gain operational amplifiers. Each amplifier is internally frequency-compensated, helping it maintains stable operation without requiring external compensation components.

The IC operates from a single power supply across a wide voltage range. It can also use split power supplies when required. Its low supply-current drain remains relatively stable as the supply voltage changes. The input common-mode range includes the negative supply rail, allowing the LM2902-N to sense signals close to ground.

However, the LM2902-N is not a rail-to-rail op-amp. Its input and output cannot normally reach the positive supply rail. If you are interested in purchasing the LM2902-N, feel free to contact us for pricing and availability.

LM2902N Pinout and CAD Models

LM2902N Pinout

Pin Name	Pin No.	Type	Rewritten Description
OUTPUT1	1	O	Amplified output from Channel 1
INPUT1−	2	I	Inverting signal input for Channel 1
INPUT1+	3	I	Non-inverting signal input for Channel 1
V+	4	P	Positive power-supply connection
INPUT2+	5	I	Non-inverting signal input for Channel 2
INPUT2−	6	I	Inverting signal input for Channel 2
OUTPUT2	7	O	Amplified output from Channel 2
OUTPUT3	8	O	Amplified output from Channel 3
INPUT3−	9	I	Inverting signal input for Channel 3
INPUT3+	10	I	Non-inverting signal input for Channel 3
GND	11	P	Ground connection for single-supply operation or negative supply connection for dual-supply operation
INPUT4+	12	I	Non-inverting signal input for Channel 4
INPUT4−	13	I	Inverting signal input for Channel 4
OUTPUT4	14	O	Amplified output from Channel 4

CAD Models

LM2902N Technical Specifications

Product Attribute	Specification
Manufacturer	Texas Instruments
Series	LinCMOS
Packaging	Tube
Product Status	Active
Amplifier Type	Standard general-purpose amplifier
Number of Circuits	4
Gain-Bandwidth Product	1 MHz
Input Bias Current	45 nA
Input Offset Voltage	2 mV
Supply Current	1.5 mA
Output Current per Channel	40 mA
Minimum Supply-Voltage Span	3 V
Maximum Supply-Voltage Span	32 V
Operating Temperature	−40°C to +85°C (TJ)
Mounting Type	Through-hole
Package/Case	14-DIP (0.300 in, 7.62 mm)
Supplier Device Package	14-PDIP
Base Product Number	LM2902

LM2902N Features and Advantages

Features

• Four op-amps in one package: Contains four independent operational amplifiers in a single IC.

• Internally frequency-compensated: Supports stable unity-gain operation without external compensation components.

• High DC voltage gain: Provides a typical open-loop voltage gain of 100 dB.

• 1 MHz bandwidth: Suitable for low-frequency and general-purpose signal processing.

• Wide supply range: Operates from a 3 V to 32 V single supply or ±1.5 V to ±16 V dual supplies.

• Low supply current: Draws approximately 700 µA, with limited dependence on supply voltage.

• Low input bias current: Has a typical input bias current of 45 nA.

• Low input offset: Offers a typical input offset voltage of 2 mV and offset current of 5 nA.

• Ground-sensing input: Its input common-mode range includes the negative supply rail or ground.

• Wide output swing: The output can approach ground and typically reaches up to about 1.5 V below the positive rail.

Advantages

• Supports single-supply circuits: Often removes the need for separate positive and negative supplies.

• Saves board space: Four amplifiers reduce component count and PCB area.

• Suitable for battery-powered equipment: Low current consumption helps reduce power use.

• Processes ground-referenced signals: Inputs and outputs can operate close to ground.

• Temperature-compensated performance: Bandwidth and input bias current remain more consistent as temperature changes.

How Does the LM2902N Work Internally?

The LM2902N contains four independent operational amplifiers that share the same power-supply connections. The diagram shows the internal circuit of one amplifier channel. Each channel compares the voltages applied to its inverting (−) and non-inverting (+) inputs. It then amplifies the difference between these two voltages.

At the input stage, transistors Q1 to Q4 form the differential input circuit. Current sources and transistors Q8 and Q9 establish stable operating currents and convert the input difference into a signal for the next stage. When one input voltage changes relative to the other, the internal current distribution changes accordingly.

The signal then passes through the high-gain stage formed mainly by Q10 and Q11. Capacitor C_Cprovides internal frequency compensation, helping prevent unwanted oscillation when negative feedback is used. The remaining transistors form the output stage, which supplies or sinks current to drive the output. In a closed-loop circuit, external feedback continuously adjusts the output until the two input voltages are nearly equal.

Understanding the LM2902N Input and Output Limits

The LM2902N input common-mode range includes ground when operated from a single supply. This allows it to measure signals close to 0 V. However, the input voltage should normally remain at least 1.5 V below the positive supply rail at room temperature. More headroom may be required across the full operating-temperature range. For example, with a 5 V supply, the recommended input range generally extends from 0 V to about 3.5 V.

The output can also swing close to ground, especially with a light load, but it cannot normally reach the positive supply rail. Its highest output level is typically about 1.5 V below V+, and the available swing becomes smaller with heavier loads. Therefore, a 5 V supply cannot produce a full 0–5 V output signal.

The required input and output voltages must remain within these limits. Otherwise, the output may clip, saturate, respond slowly, or produce an inaccurate signal. Exact limits depend on supply voltage, load current, temperature, and manufacturer specifications.

How to Utilize the LM2902N Op-Amp

The LM2902N can be used by first connecting pin 4 to the positive power supply and pin 11 to ground for single-supply operation. A 0.1 µF ceramic bypass capacitor should be placed close to these supply pins to reduce noise. The required input signal is then connected to one amplifier channel, while resistors are added to create negative feedback and set the voltage gain.

The circuit shown uses Channel 1 as a non-inverting amplifier. The input signal from potentiometer RV1 is connected to the non-inverting input at pin 3. Resistor R1 connects the inverting input at pin 2 to ground, while R2 connects the output at pin 1 back to the inverting input.

The voltage gain is calculated as:

With an input of approximately 0.73 V, the expected output is about 7.37 V. Before building the circuit, confirm that the input, output, supply voltage, and load remain within the LM2902N operating limits. Properly connect unused channels to prevent unstable or noisy outputs.

LM2902N Circuit Design and Gain Calculations

The LM2902N uses external feedback resistors to control its closed-loop voltage gain. Before selecting resistor values, define the input range, required output range, supply voltage, signal frequency, and load. The calculated output must stay within the LM2902N input and output limits to prevent clipping or inaccurate operation.

Non-Inverting Amplifier

A non-inverting amplifier produces an output with the same polarity as the input. Its voltage gain is:

If R_f=9.1kΩ and Rg=1kΩ:

For a 0.5 V input:

V_out=0.5×10.1=5.05V

Inverting Amplifier

An inverting amplifier reverses the signal polarity. Its gain is:

If Rf=20kΩ and Rin=10kΩ:

A 0.5 V input produces an ideal output change of −1 V relative to the circuit’s reference voltage. A single-supply circuit may require a mid-supply reference because the LM2902N cannot generate a negative output when powered only by positive voltage and ground.

Voltage Follower

A voltage follower connects the output directly to the inverting input. Its gain is:

Av=1

The output follows the input voltage. This configuration provides high input impedance and lower output impedance, making it useful for buffering a signal without increasing its voltage.

Bandwidth Check

The available bandwidth decreases as the closed-loop gain increases. It can be estimated using:

With a gain-bandwidth product of approximately 1 MHz and a gain of 10:

This is only an estimate. The final design must also consider slew rate, resistor tolerance, input offset, load current, temperature, and output-voltage swing.

Practical LM2902N Application Circuits

LM2902N Non-Inverting Amplifier

In the first circuit, one LM2902N channel works as a non-inverting amplifier. The 300 mV signal enters the non-inverting input, while resistors R0 and R1 form the negative-feedback network. The LM2902N compares the voltages at its two inputs and automatically adjusts the output until the feedback voltage at the inverting input is almost equal to the input signal.

R0 returns part of the output voltage to the inverting input, while R1 connects it to ground. Their resistance ratio controls how much the input signal is amplified. With R0 at 100 kΩ and R1 at 10 kΩ, the circuit has a gain of 11. Therefore, the 300 mV input becomes approximately 3.3 V at the output. This circuit functions as a signal amplifier without reversing the signal polarity.

LM2902N Instrumentation Amplifier

In the second circuit, three LM2902N channels form an instrumentation amplifier. The first two channels receive input voltages V₁ and V₂. They provide high input impedance, preventing the circuit from placing a heavy load on the connected sensors or signal sources. Resistors R1 and R_gcontrol the gain of this first stage.

The third channel works as a differential amplifier. It compares the outputs of the first two channels, rejects voltage that is common to both signals, and amplifies their difference. The circuit produces an output proportional to V₂-V₁. This function is useful when a small differential signal must be separated from unwanted common noise. Accurate resistor matching is necessary for good measurement accuracy and noise rejection.

LM2902N vs Similar Operational Amplifiers

Operational Amplifier	Channels	Supply Range	Typical Bandwidth	Input Type	Main Difference
LM2902N	4	3–26 V or ±1.5–±13 V	1 MHz	Bipolar	Quad amplifier with a −40°C to +85°C temperature range
LM324N	4	3–32 V or ±1.5–±16 V	1 MHz	Bipolar	Similar pinout with a wider supply range but a narrower 0°C to +70°C rating
LM2902B	4	3–36 V or ±1.5–±18 V	1.2 MHz	Bipolar	Newer drop-in option with improved offset, EMI filtering, and temperature performance
LM358N	2	3–32 V or ±1.5–±16 V	1 MHz	Bipolar	Provides two amplifiers instead of four
LM2904N	2	3–26 V or ±1.5–±13 V	1 MHz	Bipolar	Dual-channel version with a similar temperature range
TL074	4	Typically 7–36 V	3 MHz	JFET	Faster, higher input impedance, but its input range does not include ground

Alternatives and Replacements

• LM2902B

• LM2902BA

• LM2902K

• LM2902KV

• LM2902KAV

• LM2902-Q1

• LM324N, etc.

Mechanical Dimensions

Manufacturer

Texas Instruments has extensive capabilities in designing and manufacturing analog semiconductors such as the LM2902N. Its production process includes wafer fabrication, wafer probing, die assembly, 14-pin PDIP packaging, electrical testing, and final quality inspection. TI operates internal wafer fabrication and assembly-and-test facilities, providing greater control over product quality, production capacity, and supply continuity. During manufacturing, each device is tested to confirm that it meets specified electrical requirements, including voltage gain, bandwidth, input offset voltage, bias current, supply current, and temperature limits. TI also conducts qualification and ongoing reliability monitoring and provides material-compliance information for the LM2902N/NOPB, which is RoHS- and REACH-compliant and uses a NiPdAu lead finish.

Datasheet PDF

LM2902N Datasheets:

Frequently Asked Questions [FAQ]

1. How should unused LM2902N amplifier channels be connected?

Configure each unused channel as a voltage follower. Connect its output to the inverting input and connect the non-inverting input to ground or another valid reference voltage. Do not leave the inputs floating because they may collect noise and switch unpredictably.

2. Can the LM2902N be used as a comparator?

It can perform slow, basic voltage comparisons, but it is designed as an op-amp. Saturation recovery may be slow, and the output is not intended for fast switching. A dedicated comparator is better for precise or high-speed detection.

3. Why should a bypass capacitor be placed near the LM2902N?

A 0.1 µF ceramic capacitor between the supply pins helps absorb high-frequency noise and sudden current changes. Place it close to pins 4 and 11 with short connections for effective decoupling.

4. Can the LM2902N directly drive a relay, motor, or high-power LED?

No. Its output is intended for small signal loads and cannot safely deliver the current required by most relays, motors, or power LEDs. Use an external transistor or MOSFET with the necessary protection components.

5. What causes crossover distortion in an LM2902N AC amplifier?

Its output stage may produce distortion near the point where sourcing changes to sinking current, especially with an AC-coupled load. A suitable resistor from the output to ground can increase bias current and reduce this effect.

6. How does resistor value affect LM2902N circuit accuracy?

Very high resistor values increase errors caused by input bias current, noise, and leakage. Very low values increase output loading and power use. Values in the low-kilohm to several-hundred-kilohm range are common, depending on the circuit.

7. What must be checked before replacing an LM2902N with another op-amp?

Verify the pinout, package, supply range, input common-mode range, output swing, bandwidth, offset voltage, output current, temperature rating, and capacitive-load stability. A pin-compatible part is not automatically an electrically safe replacement.