TRI-STATE Dual 1 of 4 Line Data Selector/Multiplexer# DM74ALS253 Dual 4-Input Multiplexer with 3-State Outputs Technical Documentation
Manufacturer : National Semiconductor (NS)
## 1. Application Scenarios
### Typical Use Cases
The DM74ALS253 serves as a dual 4-input multiplexer with independent 3-state outputs, making it ideal for:
- Data routing and selection in microprocessor systems
- Bus-oriented systems where multiple devices share common data lines
- Memory address decoding and selection circuits
- Input port expansion for microcontroller systems
- Signal switching in digital communication systems
### Industry Applications
- Computer Systems : Used in bus interface units for CPU-to-peripheral communication
- Telecommunications : Employed in digital switching systems for channel selection
- Industrial Control : Applied in PLC input/output expansion modules
- Automotive Electronics : Utilized in multiplexed sensor data acquisition systems
- Test and Measurement : Incorporated in automated test equipment for signal routing
### Practical Advantages and Limitations
#### Advantages:
- 3-State Outputs : Allow multiple devices to share common bus lines without contention
- High-Speed Operation : ALS technology provides fast propagation delays (typically 9ns)
- Low Power Consumption : Advanced Low-Power Schottky technology reduces power requirements
- Wide Operating Voltage : Compatible with standard 5V TTL systems
- Independent Control : Separate output enable inputs for each multiplexer
#### Limitations:
- Limited Fan-out : Standard TTL fan-out of 10 unit loads
- Power Supply Sensitivity : Requires stable 5V ±5% power supply
- Temperature Constraints : Operating range typically 0°C to 70°C commercial grade
- Speed Limitations : Not suitable for ultra-high-speed applications (>50MHz)
## 2. Design Considerations
### Common Design Pitfalls and Solutions
#### Pitfall 1: Bus Contention
Issue : Multiple enabled devices driving the same bus line simultaneously
Solution : Implement strict output enable control sequencing and use pull-up/pull-down resistors
#### Pitfall 2: Signal Integrity
Issue : Reflections and ringing on long transmission lines
Solution : Add series termination resistors and maintain proper impedance matching
#### Pitfall 3: Power Supply Noise
Issue : Switching noise affecting device performance
Solution : Use decoupling capacitors (0.1μF ceramic) close to power pins
### Compatibility Issues
#### TTL Compatibility:
- Fully compatible with standard TTL logic levels
- Inputs: VIH = 2.0V min, VIL = 0.8V max
- Outputs: VOH = 2.7V min, VOL = 0.5V max
#### Mixed Logic Families:
- Direct interface with other ALS series devices
- Requires level shifting for interfacing with CMOS (74HC series)
- Not directly compatible with 3.3V logic without level translation
### PCB Layout Recommendations
#### Power Distribution:
- Use dedicated power and ground planes
- Place decoupling capacitors within 0.5" of each power pin
- Implement star grounding for analog and digital sections
#### Signal Routing:
- Keep select and enable lines away from clock signals
- Route critical signals (A, B inputs) as matched-length pairs
- Maintain 50Ω characteristic impedance for high-speed traces
#### Thermal Management:
- Provide adequate copper pour for heat dissipation
- Ensure proper airflow in high-density layouts
- Consider thermal vias for heat transfer to inner layers
## 3. Technical Specifications
### Key Parameter Explanations
#### DC Characteristics:
- Supply Voltage (VCC) : 4.5V to 5.5V
- Input High Voltage (VIH) : 2.0V minimum
- Input Low Voltage (VIL) : 0.
