Overview
The CD74HC238EG4 is a 3-to-8 line decoder/demultiplexer produced by Texas Instruments. This component is part of the HC (High-Speed CMOS) logic family and is designed for high-speed applications. It features three address select inputs (A2, A1, and A0) and three enable inputs (G2, G1, and G0) to control the eight output lines. The device operates in a wide voltage range from 2 V to 6 V, making it versatile for various system designs.
The CD74HC238EG4 is particularly useful in memory address decoding, data routing, and other applications where demultiplexing is required. Its balanced propagation delay and transition times, along with significant power reduction compared to LSTTL logic ICs, make it an efficient choice for modern electronic systems.
Key Specifications
| Parameter | Min | Typ | Max | Unit |
|---|---|---|---|---|
| VCC (Supply Voltage Range) | 2 | 6 | V | |
| VI (Input Voltage Range) | 0 | VCC | V | |
| VO (Output Voltage Range) | 0 | VCC | V | |
| TA (Operating Temperature Range) | -55 | 125 | °C | |
| tpd (Address to Output Propagation Delay at VCC=5V, CL=15pF) | 13 | 30 | ns | |
| tt (Output Transition Time at VCC=5V, CL=15pF) | 15 | 22 | ns | |
| Cpd (Power Dissipation Capacitance at CL=15pF) | 67 | pF | ||
| Ci (Input Capacitance) | 10 | pF |
Key Features
- Select one of eight data outputs: Active high for '238.
- Three enable inputs (G2, G1, and G0) to simplify cascading and demultiplexing.
- Wide operating temperature range: -55°C to 125°C.
- Balanced propagation delay and transition times.
- Significant power reduction compared to LSTTL logic ICs.
- HC types: 2 V to 6 V operation, high noise immunity.
- HCT types: 4.5-V to 5.5-V operation, direct LSTTL input logic compatibility.
- Fanout capability: Up to 15 LSTTL loads for bus driver outputs and 10 LSTTL loads for standard outputs.
Applications
- Memory address decoding.
- Data routing and demultiplexing.
- I/O port or memory selector applications.
- High-speed digital systems requiring efficient decoding and demultiplexing functions.
Q & A
- What is the primary function of the CD74HC238EG4?
The primary function of the CD74HC238EG4 is to act as a 3-to-8 line decoder/demultiplexer, selecting one of eight data outputs based on the input address and enable signals.
- What is the voltage range for the CD74HC238EG4?
The CD74HC238EG4 operates within a voltage range of 2 V to 6 V.
- What are the enable inputs used for in the CD74HC238EG4?
The three enable inputs (G2, G1, and G0) are used to simplify cascading and to facilitate demultiplexing. When any of these inputs are active, they force all outputs into a specific state (low for '238).
- What is the typical propagation delay of the CD74HC238EG4 at VCC=5V and CL=15pF?
The typical propagation delay is 13 ns at VCC=5V and CL=15pF.
- What is the fanout capability of the CD74HC238EG4?
The device can drive up to 15 LSTTL loads for bus driver outputs and up to 10 LSTTL loads for standard outputs.
- What are the operating temperature limits for the CD74HC238EG4?
The operating temperature range is from -55°C to 125°C.
- How does the CD74HC238EG4 differ from the CD74HC138?
The CD74HC238EG4 has active high outputs when selected, whereas the CD74HC138 has active low outputs when selected.
- What are some common applications of the CD74HC238EG4?
Common applications include memory address decoding, data routing, and I/O port or memory selector applications.
- What is the input capacitance of the CD74HC238EG4?
The input capacitance is 10 pF.
- How does the CD74HC238EG4 handle power dissipation?
The power dissipation capacitance (Cpd) is 67 pF at CL=15pF, which helps in determining the dynamic power consumption.
