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STMicroelectronics LM311N
- Part No.:
- LM311N
- Manufacturer:
- STMicroelectronics
- Category:
- Comparators
- Package:
- 8-DIP (0.300", 7.62mm)
- Datasheet:
-
LM311N.pdf
- Description:
- IC COMPARATOR 1 GEN PUR 8DIP
- Quantity:
- Payment:
- Shipping:
Inventory:2,036
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Product details
Overview
LM311N from STMicroelectronics is a single high-speed voltage comparator with strobe control, designed for precision level detection in mixed-signal systems. It features ±30 V differential input range, 50 mA open-collector output drive capability, and operates from +5 V to ±15 V supply rails. Used in overvoltage protection circuits, zero-crossing detectors, and TTL/RTL-compatible digital interface conditioning.
For engineers reviewing the LM311N datasheet, LM311N pinout, LM311N application, or LM311N equivalent, key selection criteria include input offset voltage (max 10 mV), strobe-enabled output disable, wide common-mode range (–14.7 V to +13 V), and compatibility with logic-level and high-voltage switching loads up to +50 V.
Technical Context
The LM311N implements a bipolar transistor-based differential pair input stage with active load and Darlington output stage, enabling fast response (200 ns typical) and rail-to-rail common-mode operation. Its strobe pin (Pin 6) provides TTL-compatible enable/disable control of the output transistor, allowing synchronized comparison windows in sampled-data systems.
It supports dual- or single-supply operation without external biasing: with +5 V only, the negative supply pin (Pin 4) connects to ground, and the output pulls down to ~0.23 V at 8 mA. Input bias current remains below 300 nA across temperature, minimizing source impedance errors in high-Z sensor interfaces.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage | +5 V to ±15 V - supports direct interfacing with 5 V logic and legacy ±15 V analog systems |
| Input Offset Voltage | Max 10 mV at +25 °C - defines minimum detectable voltage difference before output switching |
| Differential Input Range | ±30 V - allows direct comparison of signals referenced to different supply domains |
| Output Current Drive | 50 mA sink - enables direct driving of relays, LEDs, or TTL inputs without external buffer |
| Response Time | 200 ns (100 mV step, 5 mV overdrive) - suitable for kHz-range signal edge detection |
| Strobe Current | 3 mA - TTL-compatible enable input requiring standard logic gate drive strength |
| Input Bias Current | Max 300 nA - permits use with high-impedance sources (e.g., photodiode, thermocouple) |
Pinout & Package
LM311N is supplied in an 8-pin plastic DIP (Dual In-line Package), designated as N package per STMicroelectronics ordering nomenclature. This through-hole package supports manual prototyping and wave soldering in industrial control PCBs.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | Offset Null | Adjusts internal input offset via external potentiometer; unused in basic configurations |
| 2 | Inverting Input (−) | Accepts reference or threshold signal; common-mode range extends to ±30 V relative to supplies |
| 3 | Non-inverting Input (+) | Accepts sensed signal; matched input impedance minimizes common-mode error |
| 4 | Ground / Negative Supply | Reference node for single-supply (+5 V) operation; return path for output current |
| 5 | Offset Null | Second terminal for offset trim network; tied to Pin 1 for calibration |
| 6 | Strobe | TTL-active-low input that disables output transistor when high (≥2.0 V) |
| 7 | Output | Open-collector NPN - requires external pull-up to define logic high level and voltage domain |
| 8 | Positive Supply | Accepts +5 V, +12 V, or +15 V; supports asymmetric supplies (e.g., +12 V/0 V) |
Key Features
| Feature | Design Value |
|---|---|
| Wide Supply Range | +5 V single supply or ±15 V dual supply - eliminates need for level-shifting in mixed-rail systems |
| High-Voltage Output Capability | Withstands up to +50 V on output pin - enables direct interface to 24 V PLC inputs or relay coils |
| Low Input Current | Max 300 nA bias current - preserves accuracy in high-impedance sensor front-ends |
| Strobe-Controlled Output | Pin 6 enables synchronous sampling - critical for noise-immune window comparators and data acquisition gating |
| Fast Response | 200 ns propagation delay - supports detection of edges in 1–2 MHz clock-derived signals |
Applications
| Overvoltage Protection | Zero-Crossing Detection |
|---|---|
Use Scenario: Monitoring DC bus voltage in motor drives to trigger shutdown before capacitor overvoltage. IC Role / Device Role / Timing Role: High-speed comparator comparing sensed bus voltage against fixed reference; strobe disabled for continuous monitoring. Use Value: 50 mA output directly drives optocoupler LED, eliminating buffer transistor and reducing BOM count. | Use Scenario: Detecting AC line zero crossings in TRIAC dimmer control for phase-angle firing. IC Role / Device Role / Timing Role: Compares AC waveform against ground-referenced threshold; strobe synchronized to microcontroller timer interrupt. Use Value: ±30 V input range accepts full 230 VAC peak without attenuation, improving SNR and timing jitter. |
| Logic-Level Interface | Pulse Width Modulation (PWM) Comparator |
Use Scenario: Converting analog sensor outputs (e.g., 0–10 V pressure signal) into clean 5 V digital logic levels. IC Role / Device Role / Timing Role: Threshold detector with hysteresis added externally; output pulled up to 5 V for MCU GPIO input. Use Value: Input common-mode range includes ground and +5 V, enabling direct connection without level shifters. | Use Scenario: Generating PWM waveforms by comparing sawtooth ramp with control voltage in SMPS feedback loops. IC Role / Device Role / Timing Role: High-speed comparator with strobe used to blank comparator during ramp reset period. Use Value: 200 ns response ensures accurate duty cycle reproduction up to 500 kHz switching frequency. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar voltage comparator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LM393DR | Lower supply current (0.8 mA vs 11 mA), no strobe, dual channel, wider temp range (−40°C to +85°C) | Not suitable for strobe-gated sampling or high-voltage output loads (>36 V) | Select when low power and dual-channel integration outweigh strobe and high-voltage needs |
| TL331IDBVR | Single supply only (2.7–36 V), rail-to-rail input, no strobe, lower offset (7 mV max), SOT-23-5 package | Lacks ±15 V operation and high-voltage output tolerance; unsuitable for legacy industrial analog systems | Prefer for space-constrained 3.3 V/5 V embedded designs where strobe and high-voltage drive are unnecessary |
Compared with LM311N, LM393DR offers dual-channel integration and lower quiescent current but sacrifices strobe control and +50 V output capability; TL331IDBVR provides modern low-voltage efficiency and small footprint but cannot replace LM311N in ±15 V or high-side switching roles.
Availability
LM311N is available at Aetrix Electronics and suitable for overvoltage protection, zero-crossing detection, and logic-level interface applications requiring stable component supply and long-term industrial availability.
Supply support for LM311N 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, specializing in automotive, industrial, and power management ICs with strong analog and mixed-signal design heritage.
The LM311N belongs to ST's legacy precision analog comparator product line, engineered for robustness in industrial control, power conversion, and instrumentation where reliability under wide supply and temperature ranges is essential.
FAQ
What is the maximum output voltage the LM311N can switch?
The LM311N output transistor can withstand up to +50 V when sinking current, provided the negative supply (Pin 4) is at ground or negative potential. This rating applies under continuous DC conditions with adequate heatsinking; transient spikes must remain within absolute maximum limits specified in the datasheet.
Can the LM311N operate from a single +5 V supply?
Yes - connect Pin 4 (ground/negative supply) to system ground and Pin 8 (positive supply) to +5 V. The input common-mode range then spans 0 V to +3.8 V, and the output pulls low to ~0.23 V at 8 mA, compatible with standard 5 V TTL logic thresholds.
How does the strobe pin function in practical circuits?
When the strobe pin (Pin 6) is pulled high (≥2.0 V), the output transistor is turned off, forcing the output into high-impedance state regardless of input conditions. This enables time-gated comparisons - for example, sampling only during stable portions of a noisy signal or synchronizing multiple comparators in a data acquisition system.
Is an external pull-up resistor required on the output pin?
Yes - the LM311N has an open-collector output (Pin 7). An external pull-up resistor to the desired logic high voltage (e.g., 5 V, 12 V, or 24 V) is mandatory to define the high-state voltage level and provide current path for driven loads such as LEDs, optocouplers, or logic gates.
LM311N Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Package/Case:
- 8-DIP (0.300", 7.62mm)
- Series:
- -
- Packaging:
- Tube
- Product Status:
- Obsolete
- Type:
- General Purpose
- Number of Elements:
- 1
- Output Type:
- DTL, MOS, Open-Collector, Open-Emitter, RTL, TTL
- Voltage - Supply, Single/Dual (±):
- 5V ~ 30V, ±2.5V ~ 15V
- :
- 7.5mV @ ±15V
- Voltage - Input Offset (Max):
- 0.25µA @ ±15V
- Current - Input Bias (Max):
- 50mA
- Current - Output (Typ):
- 7.5mA
- Current - Quiescent (Max):
- -
- CMRR, PSRR (Typ):
- -
- Propagation Delay (Max):
- -
- Hysteresis:
- 0°C ~ 70°C
- Operating Temperature:
- -
- Grade:
- -
- Qualification:
- Through Hole
- :
- 8-DIP
LM311N FAQ
1.How can I place an order for LM311N through Aetrix?
Please submit a Request for Quotation (RFQ) for LM311N on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for LM311N reliable?
The price and inventory of LM311N are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM311N is usually 5 days.
3.What payment methods are accepted for LM311N?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM311N transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM311N?
LM311N orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM311N order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for LM311N?
For technical support, including LM311N datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM311N requirements.
6.How does Aetrix verify that LM311N is sourced from the original manufacturer or authorized distributors?
All LM311N products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that LM311N meets industry standards.
7.What is the process for return or replacement of LM311N?
All LM311N units undergo pre-shipment inspection (PSI). If there is an issue with LM311N, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The LM311N part is unused and in its original packaging.
Return procedure for LM311N:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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