SN74HCT257N

Overview

The SN74HCT257N is a quadruple 2-line to 1-line data selector/multiplexer with three-state outputs manufactured by Texas Instruments. It operates within a supply voltage range of 4.5 V to 5.5 V and features high-current outputs capable of driving system buses directly. The device provides typical propagation delays of 17 ns at 5.5 V with a 50 pF load, while maintaining low power consumption with a maximum supply current of 80 µA. Inputs are TTL-voltage compatible, and the package is a 16-pin PDIP.

Feature Summary

• Provides four independent 2-to-1 multiplexing channels with shared address selection inputs
• Features buffered inputs and outputs for direct interface with system buses
• Includes three-state outputs controlled by an active-low output enable strobe

Applications

• Bus-organized systems requiring signal multiplexing from multiple sources
• High-performance digital logic applications utilizing TTL-compatible inputs
• Data routing in computer architectures and communication equipment

Procurement Notes

Verify the specific ordering suffix 'N' corresponds to the 16-pin Plastic Dual In-Line Package (PDIP) before procurement. Confirm that the required operating temperature range aligns with the commercial grade specifications (-40°C to +85°C). Ensure the design accommodates the recommended 0.1-µF bypass capacitor near the VCC terminal to prevent power disturbances during operation.

Selection Notes

Select this component when designing bus-oriented systems that require multiplexing four-bit data sources. The HCT logic series ensures compatibility with standard TTL voltage levels, making it suitable for interfacing with legacy or mixed-logic environments. Verify that the 16-pin PDIP form factor fits the target printed circuit board layout constraints.

Part Context

This device belongs to the Texas Instruments SN74HCT257 family of high-speed CMOS logic devices. It functions as a quadruple 2-input multiplexer designed specifically for bus-organized systems. The product line supports various packaging options including SOIC and CDIP, but the 'N' suffix denotes the through-hole PDIP variant intended for general-purpose digital logic applications.

Replacement Considerations

SN74HCT257D (SOIC package)

FAQ

How does the output enable input affect the device state?

When the output enable (OE) input is at a high logic level, the three-state outputs enter a high-impedance state, effectively disconnecting them from the data lines.

What is the function of the A/B input pins?

The A/B pins serve as the address select inputs that determine which of the two data inputs (A or B) is routed to the corresponding output Y for each channel.