Texas Instruments SN74HC257D

Overview

SN74HC257D from Texas Instruments is a quadruple 2-line to 1-line data selector/multiplexer with 3-state non-inverting outputs, operating across 2 V–6 V supply, delivering 9 ns typical propagation delay at 4.5 V, ±6 mA output drive, and high-impedance enable control via active-low strobe (G). It serves as a bus interface IC in digital logic systems for routing four parallel 2-source data streams.

For engineers reviewing the SN74HC257D datasheet, SN74HC257D pinout, SN74HC257D application, or SN74HC257D equivalent, this page provides verified functional modes, SOIC-16 package dimensions, switching characteristics at CL = 50 pF and 150 pF, thermal resistance (RθJA = 73°C/W), and confirmed alternative parts for bus multiplexing in industrial control and embedded logic designs.

Technical Context

The SN74HC257D implements four independent 2:1 multiplexers sharing common address select (A/B) and active-low output-enable (G) inputs. Each channel selects between two input signals (A or B) based on the A/B logic level, while G forces all Y outputs into high-impedance when high - enabling bus sharing without contention.

Its CMOS HC-family architecture ensures low static current (≤80 µA ICC), rail-to-rail output swing, and compatibility with LSTTL loads. Input thresholds scale with VCC (VIH = 3.15 V min at 4.5 V), and output transition times are specified down to 6 ns (typical) at 6 V with CL = 50 pF.

Key Specifications

Pinout & Package

SN74HC257D is housed in 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, top-view orientation with pin 1 index area marked.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC157D (pin-identical), SN74HC257D offers identical functionality and timing; versus 74LVX257M, SN74HC257D provides broader voltage flexibility (2–6 V) and 5 V interoperability critical for industrial and legacy interface adaptation.

Availability

SN74HC257D is available at Aetrix Electronics and suitable for industrial PLC I/O expansion, digital test equipment signal routing, and embedded system bus arbitration requiring stable component supply and long-term lifecycle support.

Supply support for SN74HC257D 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 50 years of innovation in industrial, automotive, and communications markets.

The SN74HC257D belongs to TI's 74HC logic family, designed specifically for high-speed, low-power digital signal routing in bus-oriented systems where 3-state control and wide supply tolerance are essential.

FAQ

What is the maximum operating temperature range for the SN74HC257D?

The SN74HC257D is rated for operation from −40°C to +85°C ambient temperature, matching the commercial temperature grade defined in its SOIC-16 packaging specification. This range supports deployment in industrial control cabinets, factory automation hardware, and outdoor embedded gateways where ambient conditions exceed consumer-grade limits. The device's thermal resistance (RθJA = 73°C/W) ensures safe junction temperatures under typical load conditions within this envelope.

Does the SN74HC257D support 3.3 V logic levels when powered from 5 V?

Yes, the SN74HC257D supports 3.3 V logic inputs when VCC = 5 V. Its input thresholds scale with supply voltage: VIH(min) = 3.15 V and VIL(max) = 1.35 V at VCC = 4.5 V, making it compatible with standard 3.3 V CMOS outputs. This allows direct interfacing with 3.3 V microcontrollers controlling the A/B and G inputs while driving 5 V bus loads - a key advantage over LV-family alternatives that lack 5 V tolerance.

How does the SN74HC257D differ from the SN74HC258D?

The SN74HC257D features non-inverting outputs, whereas the SN74HC258D provides inverted outputs - a functional distinction confirmed in the TI datasheet's function table and block diagrams. Both share identical pinouts, timing (tpd = 9 ns vs. 12 ns typ), and electrical specs, but output polarity determines suitability: SN74HC257D preserves signal phase for bus drivers, while SN74HC258D suits active-low enable paths or complemented logic trees.

Can unused inputs on the SN74HC257D be left floating?

No, unused inputs on the SN74HC257D must be tied to VCC or GND. Floating CMOS inputs cause increased ICC, unpredictable output states, and potential oscillation due to noise coupling. TI's datasheet explicitly mandates this in Section 5.2: "All unused inputs of the device must be held at VCC or GND to ensure proper device operation." For example, if only two of four channels are used, the unconnected A2/B2, A3/B3, and associated Y2/Y3 pins should be terminated to avoid metastability.

Is the SN74HC257D pin-compatible with older 74LS257 devices?

No, the SN74HC257D is not pin-compatible with 74LS257. While both are quad 2:1 multiplexers, the 74LS257 uses a different pin assignment: its strobe (G) is on pin 1 (not pin 15), and outputs Y0–Y3 occupy pins 3, 4, 10, and 11 - conflicting with SN74HC257D's A/B inputs and G location. Direct replacement requires PCB redesign. Use SN74HC257D only in new designs or where layout accommodates its SOIC-16 pinout per Figure 4 of SCLS224C.