Texas Instruments LM311M

Overview

LM311M from Texas Instruments is a precision voltage comparator IC with open-collector output, designed for single-supply (5V) or dual-supply (±15V) operation in industrial and embedded signal conditioning systems. It delivers 200 ns response time, ±30 V differential input voltage range, 7.5 mV max input offset voltage at 25°C, and supports strobe-controlled output disable for synchronized system timing in relay drivers and zero-crossing detectors.

For engineers reviewing the LM311M datasheet, LM311M pinout, LM311M application, or LM311M equivalent, this page provides verified technical context, package-specific pin functions, real-world use cases in level-shifting interfaces and peak detection circuits, and validated alternative options for temperature- and supply-voltage-constrained designs.

Technical Context

The LM311M implements a bipolar transistor-based comparator architecture with independent strobe control (Pin 6) and offset null adjustment (Pins 1 and 5), enabling precise threshold setting and synchronous output gating without affecting input common-mode range. Its open-collector output supports rail-to-rail sinking up to 50 mA and can interface directly with TTL, DTL, MOS, or relay loads referenced to ground, V+, or V−.

Unlike op-amp-based comparators, the LM311M features isolated inputs and outputs-neither input nor output requires connection to system ground-making it suitable for floating-sense applications such as isolated current monitoring and transformer-coupled signal detection. Strobe functionality allows dynamic output disable during critical timing windows, reducing EMI and preventing false triggering in noisy environments.

Key Specifications

Pinout & Package

LM311M is packaged in an 8-pin SOIC (D package), 1.75 mm maximum height, RoHS-compliant with Sn lead finish and MSL Level-1 rating. The package supports surface-mount reflow up to 260°C peak and is compatible with standard 0.050" pitch PCB footprints.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar voltage comparator applications.

Compared with LM311M, LM393DR offers dual-channel integration but sacrifices strobe control and high-voltage input range, while TLV3011DBVR provides rail-to-rail operation at lower supply voltages but lacks the robustness needed for industrial relay driving and floating-sense topologies.

Availability

LM311M is available at Aetrix Electronics and suitable for relay control systems, zero-crossing detection circuits, and peak voltage monitoring applications requiring stable component supply across commercial temperature ranges and long-lifecycle production programs.

Supply support for LM311M includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor leader specializing in analog and embedded processing technologies, with decades of experience in precision signal chain components and industrial-grade IC design.

The LM311M belongs to TI's legacy voltage comparator product line, engineered specifically for robust, high-voltage, strobe-capable signal comparison in industrial automation, power conversion, and test equipment where reliability under variable supply and load conditions is critical.

FAQ

What is the maximum differential input voltage specification for the LM311M?

The LM311M supports a differential input voltage range of ±30 V, as specified in its Absolute Maximum Ratings table. This allows the device to compare signals with large potential differences-such as across shunt resistors in high-side current sensing or between phases in motor drives-without damage or clipping. This rating applies across the full 0°C to +70°C operating temperature range and is independent of supply voltage configuration.

Can the LM311M operate from a single 5V supply?

Yes, the LM311M is explicitly rated to operate from a single 5V supply, as confirmed in the Features section of the official datasheet. In this configuration, Pin 4 connects to ground, Pin 7 to +5V, and the output (Pin 8) requires an external pull-up resistor to +5V. Input common-mode range remains functional down to −0.3 V and up to V+ − 1.5 V, supporting direct interfacing with 3.3 V or 5 V logic sources.

What is the correct way to use the strobe pin (Pin 6) on the LM311M?

The strobe pin (Pin 6) must be driven with a current sink of 2.0–5.0 mA to disable the output-never shorted to ground. A typical implementation uses an NPN transistor or logic gate output configured as a current sink. When strobe current is applied, the output transistor turns off completely, presenting high impedance. Removing strobe current restores normal comparator operation. Grounding Pin 6 causes undefined behavior and risks damage.

Does the LM311M have built-in hysteresis?

No, the LM311M does not include internal hysteresis. Hysteresis must be added externally using positive feedback from the output (Pin 8) to the non-inverting input (Pin 3) or offset null pin (Pin 5), as shown in Figures 40–42 of the datasheet. Typical implementations yield 1–3 mV of hysteresis, which prevents oscillation near threshold crossings in noisy or slow-slew-rate applications. The absence of internal hysteresis preserves flexibility in setting custom thresholds and noise margins.

What is the purpose of Pins 1 and 5 on the LM311M?

Pins 1 and 5 are offset null terminals used together with an external 5 kΩ potentiometer to minimize input offset voltage. Pin 1 connects to one end of the pot, Pin 5 to the other end, and the wiper connects to V− (Pin 4). Adjusting the potentiometer balances internal transistor mismatches, reducing DC error-critical in precision threshold detection, peak hold circuits, and low-level signal comparison where even millivolt errors affect system accuracy. The LM311M datasheet specifies 7.5 mV max offset before nulling.