onsemi MC74ACT05DG Hex Inverter with Open-Drain Outputs: Datasheet, Pinout, and Application Circuit Guide

The MC74ACT05DG from onsemi is a high-speed, hex inverter integrated circuit belonging to the advanced ACT logic family. What sets this device apart from a standard hex inverter (like the 74ACT04) is its open-drain outputs. This specific feature provides exceptional flexibility for interfacing, level shifting, and implementing wired logic functions, making it a versatile component in digital design.

This guide provides a detailed overview of the IC's datasheet, pin configuration, and practical application circuits.

Datasheet Overview and Key Specifications

The datasheet for the MC74ACT05DG outlines its electrical and operational characteristics. Key specifications include:

Logic Type: Hex Inverter with Open-Drain Outputs

Number of Circuits: 6

Supply Voltage Range (VCC): 4.5V to 5.5V (standard for 5V TTL logic)

High-Speed Performance: Typical propagation delay of <10 ns

Output Capability: The open-drain structure can sink up to 24 mA per output but cannot source current.

TTL-Compatible Inputs: Inputs are compatible with TTL voltage levels, allowing for easy interfacing with older logic families.

Operating Temperature Range: -40°C to +85°C (industrial grade)

The open-drain output is the most critical feature. Unlike a push-pull output that actively drives a signal high or low, an open-drain output only has a transistor that can pull the output line to ground (LOW). When the transistor is off, the output is in a high-impedance (high-Z) state, effectively disconnected. An external pull-up resistor is required to pull the output HIGH to a desired voltage level (VCC or even a different voltage).

Pinout Configuration

The MC74ACT05DG is housed in a standard 14-pin SOIC package. The pinout is as follows:

Pin 1 (Input A1): Input for the first inverter.

Pin 2 (Output Y1): Open-drain output for the first inverter.

Pin 3 (Input A2): Input for the second inverter.

Pin 4 (Output Y2): Output for the second inverter.

Pin 5 (Input A3): Input for the third inverter.

Pin 6 (Output Y3): Output for the third inverter.

Pin 7 (GND): Ground (0V reference).

Pin 8 (Output Y4): Output for the fourth inverter.

Pin 9 (Input A4): Input for the fourth inverter.

Pin 10 (Output Y5): Output for the fifth inverter.

Pin 11 (Input A5): Input for the fifth inverter.

Pin 12 (Output Y6): Output for the sixth inverter.

Pin 13 (Input A6): Input for the sixth inverter.

Pin 14 (VCC): Positive supply voltage (typically +5V).

Application Circuit Guide

The open-drain outputs enable several key applications:

1. Level Shifting:

This is one of the most common uses. Since the output is pulled high by an external resistor to any voltage (within the output transistor's maximum voltage rating), the MC74ACT05DG can easily interface between logic families with different voltage levels. For example, you can connect a 5V logic input to the inverter and use a pull-up resistor to 3.3V on the output, effectively converting a 5V signal down to a 3.3V signal.

2. Wired-AND Configuration:

Multiple open-drain outputs can be connected together to a single pull-up resistor, creating a wired-AND logic function. The common output line will only be HIGH if all individual output transistors are off. If any one output is active (LOW), it pulls the entire bus line LOW. This is fundamental for I²C and other bus interfaces.

3. Driving Indicator LEDs:

The outputs are excellent for directly driving LEDs. The anode of the LED is connected to a positive supply (through a current-limiting resistor), and the cathode is connected to the output pin. When the output is logic LOW, it sinks current and illuminates the LED. The 24mA sink capability is more than sufficient for most standard LEDs.

4. Interfacing with High-Current/High-Voltage Loads:

The inverter can be used to control loads that require a higher voltage than VCC. The open-drain output can be pulled up to a higher voltage rail (e.g., 12V) through a relay or transistor, allowing a 5V logic circuit to control a much larger load safely.

ICGOODFIND: The onsemi MC74ACT05DG is an exceptionally useful IC due to its open-drain output architecture. Its primary strengths lie in its ability to perform level translation, facilitate bus arbitration through wired-AND connections, and directly drive various loads like LEDs. For any digital design requiring interface flexibility beyond standard logic levels, the MC74ACT05DG is an indispensable component.

Keywords: Open-Drain Outputs, Level Shifting, Hex Inverter, Wired-AND Logic, Bus Interface