Texas Instruments SN74HC257DT

Overview

SN74HC257DT from Texas Instruments is a quadruple 2-line to 1-line data selector/multiplexer with 3-state non-inverting outputs, designed for bus interface in high-performance digital systems. It operates from 2 V to 6 V, delivers ±6-mA output drive at 5 V, exhibits typical propagation delay of 9 ns (VCC = 4.5 V, CL = 50 pF), and draws ≤80 µA ICC, enabling low-power multiplexing in industrial control and instrumentation.

For engineers reviewing the SN74HC257DT datasheet, SN74HC257DT pinout, SN74HC257DT application, or SN74HC257DT equivalent, key selection criteria include its 3-state enable-controlled output behavior, non-inverted logic function, SOIC-16 package compatibility, and guaranteed operation across −40°C to +85°C ambient temperature.

Technical Context

The SN74HC257DT implements four independent 2:1 multiplexers sharing common address select (A/B) and active-low strobe (G) inputs. Each channel routes either input A or B to its corresponding Y output based on the A/B state, while G forces all outputs into high-impedance when high. Its CMOS HC-family architecture ensures TTL-compatible input thresholds and rail-to-rail output swing.

Functional mode is fully defined by Table 7-1: G = H yields Z (high-Z) regardless of A/B; G = L selects A when A/B = L (Y = A), or B when A/B = H (Y = B). No internal latching or clocking is present - it is purely combinational with 3-state control.

Key Specifications

Pinout & Package

SN74HC257DT uses a 16-pin SOIC (D) package measuring 9.90 mm × 3.90 mm with standard 1.27-mm pitch. Pin numbering follows JEDEC MS-012, with Pin 1 in top-left corner marked by index area.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 2:1 multiplexer applications.

Compared with SN74HC257DT, SN74HC157DR offers identical performance with active supply chain support, while SN74HCT257N trades lower voltage flexibility for enhanced noise margin - making the former ideal for new designs and the latter suitable only for specific 5-V TTL hybrid systems.

Availability

SN74HC257DT is available at Aetrix Electronics and suitable for industrial control, test instrumentation, and embedded peripheral expansion requiring stable component supply despite its obsolete status - we maintain legacy inventory and offer cross-reference assistance.

Supply support for SN74HC257DT includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and logic solutions with over 90 years of innovation in industrial, automotive, and communications markets.

The SN74HC257DT belongs to TI's 74HC logic family, engineered for high-speed, low-power, pin-compatible replacements of legacy TTL multiplexers in space-constrained and energy-sensitive applications.

FAQ

Is SN74HC257DT still in production?

No, SN74HC257DT is marked obsolete by Texas Instruments per the PACKAGE OPTION ADDENDUM. However, Aetrix Electronics maintains legacy stock and provides verified, traceable units for repair and continuity programs. For new designs, SN74HC157DR is the recommended active-replacement part with identical functionality and SOIC-16 packaging.

What is the logic function of SN74HC257DT?

The SN74HC257DT implements four independent 2:1 data selectors with non-inverting 3-state outputs. When G = L, Y = A if A/B = L, or Y = B if A/B = H; when G = H, all Y outputs enter high-impedance. This behavior is confirmed in Table 7-1 of the SCLS224C datasheet and applies identically to SN74HC257DT.

Can SN74HC257DT operate at 3.3 V?

Yes, SN74HC257DT is fully specified for operation from 2 V to 6 V, including 3.3 V. At VCC = 3.3 V, VIH = 2.31 V min and VIL = 0.99 V max per Section 5.2, ensuring robust compatibility with standard 3.3-V CMOS logic families and microcontrollers.

Does SN74HC257DT require pull-up resistors on unused inputs?

Yes - per Section 5.2 and Section 9.1, all unused inputs (including A/B and G) must be tied to VCC or GND to prevent floating states that cause excessive ICC and erratic output behavior. TI specifically recommends pulling G to VCC via a resistor during power-up to ensure default high-Z output state.

What is the thermal resistance (RθJA) of SN74HC257DT?

SN74HC257DT uses the SOIC (D) package, which has RθJA = 73°C/W per Section 5.3. This value assumes standard JEDEC 2S2P board conditions and is critical for calculating junction temperature rise under worst-case power dissipation (e.g., 4 × Cpd × f × VCC²).