Overview
The MC74AC138D, produced by ON Semiconductor, is a high-speed 1-of-8 decoder/demultiplexer. This device is specifically designed 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 1-of-24 or 1-of-32 decoders using multiple MC74AC138D devices and an inverter if necessary.
Key Specifications
| Parameter | Value | Unit | Conditions |
|---|---|---|---|
| DC Supply Voltage (VCC) | −0.5 to +6.5 | V | |
| DC Input Voltage (VI) | −0.5 to VCC + 0.5 | V | |
| DC Output Voltage (VO) | −0.5 to VCC + 0.5 | V | |
| Minimum High Level Input Voltage (VIH) | 2.1 (VCC = 3.0V), 3.15 (VCC = 4.5V), 3.85 (VCC = 5.5V) | V | TA = +25°C |
| Maximum Low Level Input Voltage (VIL) | 0.9 (VCC = 3.0V), 1.35 (VCC = 4.5V), 1.65 (VCC = 5.5V) | V | TA = +25°C |
| Minimum High Level Output Voltage (VOH) | 2.9 (VCC = 3.0V), 4.4 (VCC = 4.5V), 5.4 (VCC = 5.5V) | V | IOUT = −50 μA |
| Maximum Low Level Output Voltage (VOL) | 0.1 (VCC = 4.5V), 0.1 (VCC = 5.5V) | V | IOUT = 50 μA |
| Propagation Delay (tPLH, tPHL) | 7.5-12.5 ns (E1, E2), 6.5-13.0 ns (E3) | ns | VCC = 5.0V |
| Output Sink/Source Current (IO) | ±24 mA | mA | |
| Storage Temperature Range (TSTG) | −65 to +150 | °C |
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 a 1-of-24 decoder using three devices or a 1-of-32 decoder using four devices and one inverter.
- Active LOW Mutually Exclusive Outputs: Provides eight mutually exclusive active-LOW outputs.
- Output Current Capability: Outputs can source/sink up to 24 mA.
- TTL Compatible Inputs (for MC74ACT138): The MC74ACT138 version has TTL compatible inputs.
- Pb-Free Packages: Available in Pb-free packages.
Applications
The MC74AC138D is ideally suited for high-speed bipolar memory chip select address decoding. It can be used in various applications such as:
- Memory address decoding in high-speed memory systems.
- Demultiplexing data lines in digital systems.
- Expanding decoder functionality in complex digital circuits.
- Any application requiring high-speed decoding and demultiplexing with multiple enable inputs.
Q & A
- What is the primary function of the MC74AC138D? The primary function is to act as a high-speed 1-of-8 decoder/demultiplexer.
- How many input and output lines does the MC74AC138D have? It has three binary weighted input lines (A0, A1, A2) and eight mutually exclusive active-LOW output lines (O0-O7).
- What are the enable inputs on the MC74AC138D? There are three enable inputs: two active-LOW (E1, E2) and one active-HIGH (E3).
- How can the MC74AC138D be expanded for higher-order decoding? It can be expanded to a 1-of-24 decoder using three devices or a 1-of-32 decoder using four devices and one inverter.
- What is the output current capability of the MC74AC138D? The outputs can source/sink up to 24 mA.
- Is the MC74AC138D available in Pb-free packages? Yes, it is available in Pb-free packages.
- What are the typical propagation delays for the MC74AC138D? The propagation delays range from 7.5 to 12.5 ns for E1 and E2, and from 6.5 to 13.0 ns for E3.
- What are the storage temperature ranges for the MC74AC138D? The storage temperature range is −65 to +150 °C.
- Can the MC74AC138D be used as a demultiplexer? Yes, 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 is the difference between MC74AC138 and MC74ACT138? The MC74ACT138 has TTL compatible inputs, whereas the MC74AC138 does not.
