LM358

The LM358 is the industry-standard dual operational amplifier manufactured by Texas Instruments. First introduced by National Semiconductor and now part of the TI portfolio, the LM358 has become one of the most popular and widely used op-amps in the world, available from dozens of manufacturers as a second-source device.

What makes the LM358 so versatile is its design for single-supply operation. Unlike traditional op-amps that require dual positive and negative supplies, the LM358 operates from a single supply voltage as low as 3V and as high as 32V. Critically, the input common-mode voltage range extends down to 0V (ground), which means it can accept input signals that are referenced to ground without requiring negative supply rails or DC bias circuitry.

Each amplifier in the LM358 features a PNP input stage, a high-gain second stage with Miller compensation, and a Class AB push-pull output stage. The open-loop gain is typically 100dB, and the unity-gain bandwidth is 1.1MHz. The output can source up to 20mA and sink 10mA, sufficient for driving LEDs, relays (with external transistor), and most analog circuits.

The LM358 is available in a wide variety of packages, from through-hole DIP-8 for prototyping to surface-mount SOIC-8, TSSOP-8, and even ultra-compact SOT-23-8 for space-constrained designs. It is the workhorse general-purpose op-amp found in virtually every type of electronic equipment.

The LM358 is a BJT-based operational amplifier with three main internal stages per channel:

1. Input Differential Stage: Each amplifier uses a PNP (lateral PNP in some implementations) differential pair as the input stage. The PNP architecture is what allows the common-mode input voltage to go all the way down to the negative supply (ground). The differential pair drives an NPN current mirror that acts as an active load, converting the differential current to a single-ended voltage output with high gain.

2. Gain Stage (Second Stage): A common-emitter amplifier (NPN transistor) with an active current-mirror load provides the bulk of the voltage gain — typically 60-80dB. An integrated Miller compensation capacitor creates a dominant pole that rolls off the open-loop gain at -20dB/decade, ensuring stability even at unity gain with approximately 60° phase margin.

3. Output Stage: The output uses a Class AB push-pull configuration. An NPN transistor sources current when the output needs to go high, and a PNP transistor sinks current when the output needs to go low. A bias circuit sets the quiescent current through both transistors to minimize crossover distortion. The output voltage swing typically goes from near ground (50-200mV above GND depending on load) to within about 1.5V of the positive supply.

4. Bias Reference: A shared on-chip bias reference (often a VBE-based multiplier or simple current mirror) generates stable bias currents for the input and output stages of both amplifiers.

5. Short-Circuit Protection: Output current limiting resistors or active current limit circuits protect the output transistors from damage under short-circuit conditions.

Note: Pinout is identical for DIP-8, SOIC-8, and TSSOP-8 packages. SOT-23-8 packages may have different pin ordering — refer to specific datasheet.

• Sensor signal amplification and conditioning
• Active low-pass, high-pass, and band-pass filters
• Voltage followers and impedance buffers
• Schmitt trigger comparators and level detectors
• Current sense amplifiers and transimpedance amplifiers