STMicroelectronics LM311D

Overview

LM311D from STMicroelectronics is a single high-speed voltage comparator with strobe control, designed for precision level detection in analog-to-digital interfaces and threshold monitoring circuits. It features ±30 V differential input range, 50 mA open-collector output drive capability, and operates from +5 V to ±15 V supplies. Used in overvoltage protection, zero-crossing detection, and pulse-width modulation feedback loops.

For engineers reviewing the LM311D datasheet, LM311D pinout, LM311D application, or LM311D equivalent, key selection criteria include input offset voltage (max 10 mV), strobe current (3 mA), response time (200 ns), output voltage swing up to +50 V, and SO-8 thermal performance (R_thJA = 175 °C/W).

Technical Context

The LM311D implements a bipolar transistor-based differential pair input stage with active load and Darlington output stage, enabling rail-to-rail common-mode input range (–14.7 V to +13 V at ±15 V supply) and fast propagation delay. Its strobe pin (Pin 6) enables synchronous comparison gating, critical for noise-immune sampling in switched-mode power supplies.

It supports TTL/DTL/RTL/MOS logic interfacing via its open-collector output and tolerates output voltages up to +40 V (LM311D) or +50 V (LM211D), with internal clamping limiting output short-circuit duration to 10 s. Input bias current remains ≤300 nA across 0 °C to +70 °C operating range.

Key Specifications

Pinout & Package

LM311D is housed in an SO-8 plastic micropackage (ECOPACK® compliant), 5.0 mm × 4.0 mm body, 1.27 mm pitch, with exposed pad not electrically connected. Thermal resistance R_thJA = 175 °C/W enables operation up to +70 °C ambient without forced airflow.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM311D, LM393DR offers dual functionality but lacks strobe control and speed; TL331IDBVR provides rail-to-rail input but sacrifices input range, output voltage tolerance, and response time - making LM311D uniquely suited for industrial-level detection with timing integrity.

Availability

LM311D is available at Aetrix Electronics and suitable for overvoltage protection, PWM feedback, zero-crossing detection, and analog-to-digital interface applications requiring stable component supply across industrial production cycles.

Supply support for LM311D 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing analog, microcontroller, power, and sensor solutions for automotive, industrial, and consumer markets.

The LM311D belongs to ST's legacy precision analog comparator product line, engineered for robust performance in industrial control, power conversion, and instrumentation systems where reliability under wide supply and temperature ranges is essential.

FAQ

What is the maximum output voltage the LM311D can switch?

The LM311D output can switch up to +40 V relative to the negative supply pin (Pin 4), as specified in absolute maximum ratings. This allows direct interface to 24 V industrial control lines and relay coils without external level-shifting components. Operation above this voltage risks permanent damage, and sustained output short-circuit must be limited to 10 seconds per cycle.

Does the LM311D require external pull-up resistors on its output?

Yes - the LM311D features an open-collector NPN output (Pin 6) that can only sink current. An external pull-up resistor to a positive supply (up to +40 V) is mandatory to establish a defined high logic state. Typical values range from 1 kΩ (for 5 mA drive) to 10 kΩ (for low-power logic interfacing), selected based on required rise time and load current.

Can the LM311D operate from a single +5 V supply?

Yes - the LM311D is fully specified for single +5 V operation, with input common-mode range extending from 0 V to +3.8 V and output compatible with TTL/CMOS logic thresholds. Input offset voltage remains ≤10 mV and response time stays at 200 ns, enabling use in battery-powered and USB-powered sensing modules without supply translation.

How does the strobe function affect output behavior?

When the strobe pin (Pin 5) is pulled low (≤0.8 V), the output enters high-impedance state regardless of input conditions - effectively disabling comparison. When strobe is high (≥2.0 V), normal comparator operation resumes. This enables precise timing windows for noise-immune sampling, such as capturing voltage peaks during specific phases of a switching cycle.