LM358 Pinout, Specifications & Common Mistakes

LM358 Pin Diagram

The LM358 comes in DIP-8, SOIC-8, TSSOP-8, and SOT-23-8 packages. Pin numbering is the same across all variants. The chip contains two independent op-amps (labeled A and B) sharing pins 4 (V−/GND) and 8 (V+).

Amplifier-to-Pin Mapping

If IN+ voltage > IN− voltage, the corresponding output goes HIGH (toward V+). If IN+ < IN−, the output goes LOW (toward V−). Both amplifiers operate independently — the only thing they share is the power supply.

Key Specifications

Typical Application Circuits

Non-Inverting Amplifier (Most Common LM358 Circuit)

Signal into pin 3 (IN1+). Feedback from pin 1 (OUT1) to pin 2 (IN1−) through Rf. Pin 2 to ground through Rg.

Gain = 1 + Rf/Rg. With Rf = 100 kΩ, Rg = 10 kΩ → gain of 11 (20.8 dB).

Component placement: keep the feedback resistor within 5 mm of pins 2 and 1. Keep the non-inverting input trace short. Add a 0.1 μF bypass cap directly between pin 8 and pin 4 — this is not optional.

Comparator With Hysteresis

The LM358 is an op-amp, not a comparator — but it works as a slow comparator if you add hysteresis. Without hysteresis, noise near the threshold causes the output to chatter.

Signal into pin 3 (IN1+). Reference voltage into pin 2 (IN1−). Feedback resistor from pin 1 (OUT1) to pin 3 (IN1+) — this creates positive feedback and a Schmitt-trigger action. For a 1 MΩ feedback resistor and 10 kΩ input resistor, hysteresis is roughly Vout-swing × (10k / 1M) ≈ 50 mV. Enough to kill noise without affecting the threshold significantly.

Common Mistakes When Using the LM358

1. Expecting Rail-to-Rail Input (It Isn't)

This is the #1 trap. The LM358's input common-mode range goes from V− to about 1.5–2V below V+. If both inputs exceed that upper limit, the output collapses to the low rail. High-side current sensing with the inputs near V+ is the classic failure — the amplifier appears to "stop working" when the common-mode voltage crosses the threshold. If you need inputs that reach V+, use an LMV358 or TLV9002 instead.

2. Expecting Rail-to-Rail Output (It Isn't Either)

The output can swing close to ground (within ~50 mV when lightly loaded), but on the high side it tops out at roughly V+ minus 1.5V. At a 5V supply, you get about 3.5V max output. If your ADC expects a 0–5V swing, you'll lose the top 30% of your range. Add a pull-up resistor from output to V+ (1–10 kΩ) to help the output get a little closer, but don't expect miracles.

3. Leaving the Unused Amplifier Floating

If you're only using one of the two op-amps, you cannot leave the unused one's pins disconnected. Floating inputs pick up noise and the unused amplifier oscillates or draws excess current. The correct termination: connect OUT (pin 1 or 7) to IN− (pin 2 or 6) — this configures it as a unity-gain buffer. Then connect IN+ (pin 3 or 5) to V−/GND. The unused amplifier sits quietly at its minimum output, drawing negligible current.

4. Omitting the Supply Bypass Capacitor

0.1 μF ceramic between pin 8 (V+) and pin 4 (GND), placed within 5 mm of the IC. This is not optional. Without it, the LM358 can oscillate at high frequencies — especially when driving capacitive loads or long traces. The oscillation may be invisible on a low-bandwidth scope but causes excess current draw and erratic DC behavior. If you're driving anything with a cable attached, add a 10–100 μF electrolytic in parallel with the 0.1 μF ceramic.

5. Using It As a Comparator Without Hysteresis

The LM358 is not a comparator, but it's commonly pressed into service as one for low-speed applications. The problem: without hysteresis, any noise near the switching threshold causes the output to oscillate violently. You'll see a "fuzzy" transition or high-frequency bursts on the output. Fix: add a feedback resistor (100 kΩ–1 MΩ) from output to the non-inverting input. This creates positive feedback and a clean switching threshold with built-in noise immunity.

6. Oscillation When Driving Capacitive Loads or Transistor Bases

The LM358 does not like driving capacitance directly. Long cables, MOSFET gates, or BJT bases connected directly to the output can cause high-frequency oscillation. For capacitive loads, add a 50–100 Ω series resistor between the output and the capacitive load. For transistor bases, use a 1 kΩ series base resistor — the transistor's gain multiplies the load capacitance (Miller effect) and makes oscillation almost guaranteed without it.

7. Watch Out: Counterfeit LM311 Comparators Are Actually Relabeled LM358s

A documented problem: fake LM311 comparators purchased from uncertified sellers turn out to be relabeled LM358 op-amps. The pinouts differ significantly — on the LM358, IN+ is pin 3 and IN− is pin 2, which is reversed compared to the LM311. Drop a fake LM311 (actually an LM358) into a comparator socket and you get short-circuits, overheating, or bizarre behavior. Buy from authorized distribution.

Where to Buy LM358

Contact ICMASS for current pricing. We stock LM358 in all common packages with traceability to TI, ST, and ON Semi.

Frequently Asked Questions About LM358 Pinout

Q1: What is the pinout of the LM358?

A: Pin 1: OUT1, Pin 2: IN1−, Pin 3: IN1+, Pin 4: GND/V−, Pin 5: IN2+, Pin 6: IN2−, Pin 7: OUT2, Pin 8: VCC/V+. Amplifier A uses pins 1/2/3. Amplifier B uses pins 5/6/7. Power is shared on pins 4 and 8.

Q2: Is the LM358 rail-to-rail?

A: No. Input common-mode range extends to ground (V−) but only to about 1.5–2V below V+. Output swings to within ~50 mV of V− but only to ~1.5V below V+. If your circuit requires inputs or outputs reaching the positive rail, use a rail-to-rail alternative like the LMV358 or TLV9002.

Q3: What do I do with the unused op-amp in an LM358?

A: Never leave unused pins floating. Connect OUT to IN− (unity-gain buffer), and connect IN+ to V−/GND. The unused amplifier sits quietly at its minimum output. Floating inputs cause oscillation and excess power draw.

Q4: Can I use the LM358 as a comparator?

A: Yes, for low-speed applications. But you must add hysteresis: a feedback resistor (100 kΩ–1 MΩ) from output to the non-inverting input. Without it, noise near the threshold causes output oscillation. For dedicated comparator applications, the LM393 is a better choice — it's designed for open-collector comparator operation.

Q5: Why does my LM358 oscillate when driving a MOSFET gate?

A: The LM358 is not stable driving capacitive loads directly. Add a 50–100 Ω series resistor between the output and the MOSFET gate. For BJT bases, use a 1 kΩ series base resistor. The transistor's Miller capacitance multiplies the effective load capacitance and makes oscillation nearly guaranteed without series resistance.

Q6: What's the difference between LM358 and LM324?

A: The LM358 is a dual op-amp (2 amplifiers, 8 pins). The LM324 is a quad op-amp (4 amplifiers, 14 pins). Same silicon, same specs — same gain-bandwidth (0.7 MHz), same slew rate (0.3 V/μs), same input/output swing limits. If you need 1–2 amplifiers, use the LM358 (smaller package). If you need 3–4, use the LM324. The pinout is different because of the package, but the per-amplifier behavior is identical.

Q7: What is the minimum supply voltage for the LM358?

A: 3V for the standard LM358. At 3V, headroom is tight — the output can only swing about 1.5V peak-to-peak (from ~50 mV to ~1.5V). For 3.3V operation, this is workable but marginal. The LM358LV variant is specifically designed for low-voltage operation (1.5V to 5.5V) and has rail-to-rail output, making it a better choice for 3.3V-only designs. Per the TI LM358 datasheet.

Q8: What are common replacements or equivalents for the LM358?

A: Pin-compatible direct replacements: LM158 (military temp, −55 to +125°C), LM258 (industrial temp, −25 to +85°C). For better specs in the same pinout: LMV358 (rail-to-rail output, 1 MHz GBW), TLV9002 (rail-to-rail input/output, 1 MHz, lower power), OPA2197 (precision, 10 MHz, 20 V/μs slew rate). If you need a single op-amp instead of dual, use the LM321 (same silicon, 5-pin SOT-23).