LM358P

The LM358P from Texas Instruments is the through-hole PDIP-8 version of the LM358, one of the most widely used dual operational amplifiers in the electronics industry. First introduced in the 1970s, the LM358 family remains in high-volume production due to its simplicity, low cost, wide availability, and single-supply capability. The ‘P’ suffix specifically denotes the plastic DIP-8 package for through-hole mounting, favored in prototyping, education, and industrial applications requiring manual soldering or socket installation.

The LM358 contains two independent op-amps sharing common VCC and GND pins. Each amplifier features internal dominant-pole compensation for unity-gain stability, eliminating the need for external compensation components. The input common-mode voltage range includes ground (0 V), which is the defining feature that distinguishes the LM358 from older dual-supply op-amps like the LM741. This allows the LM358 to directly amplify signals near ground without a negative supply rail.

The output swings from approximately 5 mV above ground (no load) to VCC – 1.5 V. The output can source 40 mA and sink approximately 20 mA at VCC = 15 V, sufficient for driving LEDs, small relays, and logic-level signals. The 500-µA per-amplifier quiescent current is modest for bipolar op-amps and is essentially independent of supply voltage.

The LM358P is electrically identical to the LM358N (ON Semiconductor’s PDIP-8 version) and LM358PT (ST’s PDIP-8 version). These parts are fully interchangeable in most applications. TI also offers the LM358B (3-36 V, 3-mV Vos, EMI filtering, 1.2-MHz GBW) as a drop-in upgrade for new designs.

The LM358 is the dual-channel companion to the LM324 quad op-amp. The two devices share identical amplifier cells and specifications, differing only in channel count and package. Designers needing only two amplifiers should use the LM358 to save board space; those needing four should use the LM324.

**Bipolar Input Stage:** Each LM358 amplifier uses a PNP differential pair (Q1-Q4 in the TI schematic) with a current-mirror load. The PNP inputs allow the common-mode range to include ground and extend -0.3 V below it. The 45-nA typical input bias current is the PNP base current flowing out of the input pins. The bias current creates a voltage error across source resistances; matching the DC resistance seen by both inputs minimizes this error.

**Internal Compensation:** A 30-pF internal capacitor provides dominant-pole compensation, setting the unity-gain crossover frequency to approximately 1.1 MHz and the slew rate to 0.5 V/µs. The compensation ensures stability with 100% feedback (unity-gain voltage follower) without external components. The relatively low slew rate limits full-power bandwidth to approximately 10 kHz for large signals.

**Class-AB Output with Current Sink:** The output stage can source 40 mA (via a Darlington pull-up) and sink 20 mA (via a current-sink transistor). The asymmetric drive capability means the output cannot truly swing to ground under load — it typically sits at 5-20 mV with no pull-down resistor, and rises to hundreds of millivolts when sinking more than a few µA. A pull-down resistor (10-100 kΩ) from output to ground helps the output reach near-zero volts in DC applications.

**Single-Supply Design:** The VCC- pin (pin 4) serves as both the ground reference and the return path for the output sink current. No negative supply is required, though split-supply operation (±1.5 V to ±15 V) is also supported by connecting VCC- to the negative rail.