Onsemi MC74AC14D Hex Inverting Schmitt Trigger: Datasheet, Pinout, and Application Circuit Guide
The Onsemi MC74AC14D is a highly versatile and widely used integrated circuit belonging to the AC advanced CMOS logic family. It contains six independent inverting Schmitt trigger gates within a single 14-pin package. This device is prized for its noise immunity, ability to clean up noisy signals, and its function in converting slow input transitions into sharp, well-defined output signals. This guide provides an overview of its key specifications, pinout configuration, and a practical application circuit.
Datasheet Overview and Key Specifications
The MC74AC14D operates across a broad voltage range, typically from 2.0V to 6.0V, making it suitable for both 3.3V and 5V systems. Its key electrical characteristics, as defined in its datasheet, include:
High Noise Immunity: A hallmark of the Schmitt trigger design. It features defined positive-going (Vt+) and negative-going (Vt-) input threshold voltages. For a 5V supply, the typical threshold values are approximately Vt+ = 3.3V and Vt- = 1.7V. This hysteresis voltage (the difference between Vt+ and Vt-, typically 1.6V at 5V) ensures the input must significantly overshoot or undershoot these points to cause an output change, effectively rejecting noise.
High-Speed Performance: The AC family offers high-speed operation with typical propagation delay times of 5.0 ns at 5V.
Low Power Consumption: Despite its high speed, it maintains the low power consumption characteristic of CMOS technology.
Robust Output Drive: It can source or sink up to 24mA of current at the output, allowing it to drive relatively heavy loads, such as LEDs or other ICs, directly.
Pinout Configuration
The MC74AC14D is housed in a standard 14-pin SOIC (D) package. The pinout is as follows:
Pin 1: Input A1
Pin 2: Output Y1
Pin 3: Input A2
Pin 4: Output Y2
Pin 5: Input A3
Pin 6: Output Y3
Pin 7: Ground (GND)
Pin 8: Output Y4
Pin 9: Input A4
Pin 10: Output Y5
Pin 11: Input A5
Pin 12: Output Y6
Pin 13: Input A6
Pin 14: Supply Voltage (VCC)
Each of the six gates operates independently, sharing only the common power (VCC) and ground (GND) connections.
Application Circuit Guide: A Simple Square Wave Oscillator
One of the most common applications for a Schmitt trigger inverter is to create a simple RC oscillator (or astable multivibrator). A single gate from the MC74AC14D can be used to generate a continuous square wave.
Circuit Diagram:
Connect the following components:
1. The output (e.g., Pin 2, Y1) is fed back to the input (Pin 1, A1) through a resistor R.
2. A capacitor C is connected between the input (Pin 1, A1) and ground.
3. (Optional) A small series resistor can be added between the feedback node and the input to limit current surges.
How it Works:
1. When the output is high, it charges the capacitor C through resistor R.
2. Once the capacitor voltage exceeds the positive-going threshold (Vt+), the gate triggers, and its output switches to a low state.
3. With the output now low, the capacitor begins to discharge through R.
4. When the capacitor voltage falls below the negative-going threshold (Vt-), the gate triggers again, switching the output back to high, and the cycle repeats indefinitely.
The oscillation frequency is determined primarily by the values of the resistor (R), the capacitor (C), and the hysteresis of the IC. An approximate formula is:
f ≈ 1 / (0.8 R C)
This circuit is excellent for generating clock signals, tone generation, and timing applications where precision is not critical.
ICGOODFIND: The Onsemi MC74AC14D is an exceptionally useful IC for signal conditioning, noise filtering, and oscillator creation. Its built-in hysteresis provides superior noise rejection compared to standard logic gates, making it a fundamental component in digital and analog design for ensuring signal integrity and generating stable waveforms.
Keywords: Schmitt Trigger, Hysteresis, Signal Conditioning, Oscillator Circuit, Noise Immunity.
