Overview
The MC74AC138DT, produced by ON Semiconductor, is a high-speed 1-of-8 decoder/demultiplexer. This device is ideally suited for high-speed bipolar memory chip select address decoding. It accepts three binary weighted inputs (A0, A1, A2) and, when enabled, provides eight mutually exclusive active-LOW outputs (O0-O7). The device features multiple input enables, allowing for easy parallel expansion to higher-order decoders, such as a 1-of-24 decoder using three devices or a 1-of-32 decoder using four devices and one inverter.
Key Specifications
| Parameter | Symbol | Unit | Conditions | Typical Value | Guaranteed Limits |
|---|---|---|---|---|---|
| Minimum High Level Input Voltage | VIH | V | VOUT = 0.1 V, VCC = 5.0 V | 4.5 | 2.25 - 3.15 |
| Maximum Low Level Input Voltage | VIL | V | VOUT = 0.1 V, VCC = 5.0 V | 1.5 | 0.9 - 1.65 |
| Minimum High Level Output Voltage | VOH | V | IOUT = -50 μA, VCC = 5.0 V | 2.99 | 2.9 |
| Propagation Delay E3 to On | tPLH | ns | TA = +25°C, CL = 50 pF | 5.0 | 2.5 - 8.0 |
| Input Capacitance | CIN | pF | VCC = 5.0 V | 4.5 | - |
| Power Dissipation Capacitance | CPD | pF | VCC = 5.0 V | 60 | - |
Key Features
- Demultiplexing Capability: Can be used as an 8-output demultiplexer by using one of the active LOW Enable inputs as the data input and the other Enable inputs as strobes.
- Multiple Input Enable for Easy Expansion: Allows parallel expansion to higher-order decoders, such as 1-of-24 or 1-of-32 decoders.
- Active LOW Mutually Exclusive Outputs: Provides eight mutually exclusive active-LOW outputs.
- Outputs Source/Sink 24 mA: High current drive capability.
- TTL Compatible Inputs (ACT138): The ACT138 version has TTL-compatible input thresholds.
- Pb-Free Packages: Available in Pb-free packages, ensuring compliance with environmental regulations.
Applications
- High-Speed Bipolar Memory Chip Select Address Decoding: Ideal for high-speed memory applications requiring address decoding.
- Decoder Expansion: Can be used to create higher-order decoders such as 1-of-24 or 1-of-32 decoders.
- Demultiplexing: Can function as an 8-output demultiplexer, useful in various digital logic circuits.
- General Digital Logic Circuits: Suitable for use in a wide range of digital logic applications requiring decoding or demultiplexing functions.
Q & A
- What is the primary function of the MC74AC138DT?
The MC74AC138DT is a high-speed 1-of-8 decoder/demultiplexer, primarily used for high-speed bipolar memory chip select address decoding.
- How many inputs and outputs does the MC74AC138DT have?
The device accepts three binary weighted inputs (A0, A1, A2) and provides eight mutually exclusive active-LOW outputs (O0-O7).
- What are the enable inputs on the MC74AC138DT?
The device features three Enable inputs: two active-LOW (E1, E2) and one active-HIGH (E3).
- Can the MC74AC138DT be expanded to higher-order decoders?
Yes, it can be expanded to higher-order decoders such as 1-of-24 or 1-of-32 decoders using multiple devices and an inverter.
- What is the current drive capability of the MC74AC138DT outputs?
The outputs can source/sink up to 24 mA.
- Are the MC74AC138DT devices available in Pb-free packages?
Yes, the devices are available in Pb-free packages.
- What is the difference between the MC74AC138 and MC74ACT138?
The MC74ACT138 has TTL-compatible input thresholds, whereas the MC74AC138 does not.
- How can the MC74AC138DT be used as a demultiplexer?
It can be used as an 8-output demultiplexer by using one of the active LOW Enable inputs as the data input and the other Enable inputs as strobes.
- What are the typical propagation delays for the MC74AC138DT?
The propagation delay from E3 to On is typically around 5.0 ns at TA = +25°C and CL = 50 pF.
- What is the input capacitance of the MC74AC138DT?
The input capacitance is typically 4.5 pF at VCC = 5.0 V.
