Part Number: LM311N/NOPB

Manufacturer: Texas Instruments


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Technical Specifications of LM311N/NOPB

Datasheet  LM311N/NOPB datasheet
Category Integrated Circuits (ICs)
Family Linear – Comparators
Manufacturer Texas Instruments
Packaging Tube
Part Status Active
Type General Purpose
Number of Elements 1
Output Type DTL, MOS, Open-Collector, Open-Emitter, RTL, TTL
Voltage – Supply, Single/Dual (±) 5 V ~ 36 V, ±2.5 V ~ 18 V
Voltage – Input Offset (Max) 7.5mV @ ±15V
Current – Input Bias (Max) 0.25μA @ ±15V
Current – Output (Typ) 50mA
Current – Quiescent (Max) 7.5mA
Propagation Delay (Max)
Operating Temperature 0°C ~ 70°C
Package / Case 8-DIP (0.300″, 7.62mm)
Mounting Type Through Hole
Supplier Device Package 8-PDIP

LM311N/NOPB Introduction

The LM311-N, unlike other voltage comparators on the market, has input currents that are nearly a thousand times smaller. These comparators may function with various power inputs, from the typical 15V in op-amps to the 5V often used in IC logic. Its outputs can switch voltages up to 50V at currents as high as 50 mA, making them suitable for RTL, DTL, TTL, and MOS circuits and ideal for driving lamps or relays. These comparators pack quite a punch thanks to their isolated inputs and outputs, offset balancing, and strobe functionality. While they may be slightly slower than competing products, they are significantly less likely to experience false oscillations. These voltage comparators, with operating temperatures from 25 to +85 degrees Celsius for the LM111-N and from 0 to +70 degrees Celsius for the LM311-N, are ideal for use in a wide variety of situations.

LM311N/NOPB Description

Devices like the LM106 and LM710 are voltage comparators, but their input currents are hundreds to thousands of times higher than those of the LM111-N, LM211-N, and LM311-N. Moreover, they are made to function on a larger variety of supply voltages, from the typical 15V op-amp supply to the single 5V supply needed for IC logic. Their signals can be used in MOS, RTL, or DTL circuits. In addition, they can switch voltages up to 50V at currents as high as 50 mA, making them ideal for driving lamps or relays.

The LM111-N, LM211-N, and LM311-N may isolate their inputs and outputs from the system ground, allowing the output to power loads referenced to the ground, the positive or negative supply. Outputs can be wire ORed, and there is an offset balancing and strobe function. These devices are indeed slower than the LM106 and LM710 (200 ns vs. 40 ns reaction time), but they’re also considerably less likely to experience spurious oscillations. Like its predecessors, the LM106 and LM710, the LM111-N is distinguished by a familiar pinout. rather than a 55°C to 125°C temperature range, its performance is specified over a 25°C to +85°C temperature range. The operating temperature of the LM311-N is between freezing and boiling.

Application Hints

Circuit Techniques for Avoiding Oscillations in Comparator Applications

In most cases, the output response of a high-speed comparator like the LM111-N will be fast and stable when used with fast input signals and low source impedances, provided that the power supplies have been bypassed (with 0.1 F disc capacitors). The output signal is routed far away from the inputs (pins 2 and 3) and pins 5 and 6. A voltage ramp or slow sine wave and a signal source impedance of 1 k to 100 k can cause the comparator to oscillate close to the crossing point. This is because of the LM111-N’s strong gain and wide bandwidth compared to other comparators. Many safeguards are suggested to prevent fluctuations or instability in such an application.

Pins 5 and 6 are the trim pins and are used as extra inputs that aren’t wanted. When not used with a trim pot, these pins should be shorted. A 0.01 F capacitor C1 placed between pins 5 and 6 will reduce their sensitivity to AC coupling if wired to a trim pot. A smaller capacitor can be used if positive feedback is implemented via pin 5.

When a capacitor C2 in the range of 100 pF to 1000 pF is connected across the input pins of a comparator, the waveform that emerges from the device is cleaner for some input sources.

When a resistive network, RS, is used to transmit a signal from a source to an antenna, it is often preferable to use a similar network, RS′, for both direct current (DC) and alternating current (AC) applications. Inductive wire wound resistors are not suited for comparator input circuits, although carbon, tin-oxide, and metal-film resistors have all proven successful.

Input resistors (such as summing resistors) play a crucial role in comparator circuits; hence their value and location are crucial. The resistor’s body should always be near its device or socket. This means that the distance between the comparator and the resistor shouldn’t be too great, since this could allow for signal radiation or pickup down the lead or printed circuit foil. Similarly, capacitors, potentiometers, and so on all function similarly. If RS=10 k, for instance, even 5 inches of lead space between the resistors and the input pins can cause significant and difficult-to-control oscillations. As inserting resistors near the comparator is not an option, twisting the input leads tightly is the next best thing.

Oscillation can occur from feedback to practically every comparator pin, so careful engineering of the printed-circuit arrangement is required. The LM111-N circuitry is best supported by a ground plane, such as the bottom layer of a double-sided circuit card. Between the two, ground foil (positive or negative) should stretch to prevent any shorts. All high-level signals should be shielded from capacitive coupling by keeping the input foil connections as tiny and compact as possible and enclosing them in ground foil on all sides (such as the output). It’s recommended to short pins 5 and 6 together if they’re not being used.

Installing the 0.01 F capacitor and connecting them to a trim pot requires placing the trim pot no more than a few inches from the LM111-N. If you can’t use this capacitor, you might want to put some shielding printed-circuit foil between pins 6 and 7. The LM111-N must be close to the bypass capacitors in the power supply. (The bypass power source must be physically close by with other comparators.)

As a comparator is a strong amplifier for its own noise, it is common practice to employ hysteresis (positive feedback) around it to prevent oscillation and excessive noise on the output.


The LM111-N, LM211-N, and LM311-N voltage comparators are amazing devices with a wide range of characteristics and functionalities, to sum up. They are a dependable and adaptable option for various applications thanks to their low input currents, great compatibility with diverse circuits, and simplicity in driving high-voltage loads. Also, they are simple to install into any system and guarantee stable operation because of their separated inputs and outputs, offset balancing, and strobe capability. These comparators are perfect for your upcoming project, whether for a single 5V supply for IC logic or typical 15V op amp supplies.

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