Texas Instruments CD74HCT257E

Overview

CD74HCT257E from Texas Instruments is a quad 2-input multiplexer with three-state non-inverting outputs, designed for data routing in digital systems. It features 4.5V–5.5V operation, 12ns typical propagation delay (CL = 15pF), and -55°C to +125°C operating range. Its active-low Output Enable (OE) allows bus sharing in microcontroller peripheral interfaces.

For engineers reviewing the CD74HCT257E datasheet, CD74HCT257E pinout, CD74HCT257E application, or CD74HCT257E equivalent, key selection criteria include LSTTL-compatible input thresholds (VIL ≤ 0.8V, VIH ≥ 2.0V), high-impedance output control timing, and PDIP-16 package compatibility with legacy through-hole PCB layouts.

Technical Context

The CD74HCT257E implements four identical 2:1 multiplexer circuits sharing one Select (S) and one active-low Output Enable (OE) control line. Each channel routes either I0 or I1 to its Y output based on S state, while OE = HIGH forces all Y outputs into high-impedance mode-enabling bidirectional bus arbitration without external logic.

Its HCT logic family ensures direct interface with standard TTL inputs while maintaining CMOS power efficiency. Input leakage remains ≤±1µA across temperature, and output drive capability supports up to 15 LSTTL loads under worst-case conditions.

Key Specifications

Pinout & Package

CD74HCT257E is housed in a 16-pin plastic dual in-line package (PDIP), with 0.3-inch body width and standard through-hole mounting footprint.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar quad 2-input multiplexer applications.

Compared with CD74HCT257E, SN74HCT257N offers identical performance in a currently active TI production line, while MC74HCT257PG provides second-source availability with slightly reduced temperature range but automotive qualification.

Availability

CD74HCT257E is available at Aetrix Electronics and suitable for industrial control systems, legacy equipment repair, and aerospace subsystems requiring stable component supply and long-term obsolescence management.

Supply support for CD74HCT257E 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 high-reliability component development.

The CD74HCT257E belongs to TI's legacy High-Speed CMOS (HCT) logic family, engineered for seamless integration with TTL-based systems while delivering CMOS power efficiency and extended temperature operation.

FAQ

What is the maximum clock/data rate supported by CD74HCT257E?

The CD74HCT257E is not a clocked device but a combinational multiplexer. Its usable data rate depends on propagation delay and load capacitance. With 13ns typical tPLH/tPHL at CL = 15pF and VCC = 5V, it supports reliable switching up to approximately 35 MHz in well-designed PCB layouts with controlled impedance and proper decoupling. System-level timing must account for worst-case delays across temperature and voltage.

Does CD74HCT257E require external pull-up or pull-down resistors on its inputs?

No, CD74HCT257E does not require external pull-up or pull-down resistors on its inputs. Its CMOS inputs exhibit ≤±1µA leakage across temperature, and defined VIH/VIL thresholds ensure stable logic states with driven TTL or CMOS sources. Floating inputs must be avoided - unused inputs should be tied to VCC or GND to prevent oscillation and excess current draw.

Can CD74HCT257E operate at 3.3V supply voltage?

No, CD74HCT257E is specified only for 4.5V to 5.5V operation. At 3.3V, input thresholds (VIH ≥ 2.0V, VIL ≤ 0.8V) may not be reliably met, and output drive strength degrades significantly. For 3.3V systems, consider the CD74HC257E (2V–6V) or SN74LVC257A (1.65V–3.6V), which are functionally equivalent but rated for lower voltages.

What is the thermal resistance (θJA) of the CD74HCT257E PDIP package?

The junction-to-ambient thermal resistance (θJA) for the CD74HCT257E in its 16-pin PDIP (N) package is 67°C/W under typical JEDEC-standard board conditions. This value assumes a 1-inch² copper pad with two internal layers; actual θJA will vary with PCB layout, airflow, and copper area. Maximum junction temperature must not exceed 150°C under continuous operation.

Is CD74HCT257E compatible with lead-free soldering processes?

Yes, CD74HCT257E is RoHS-compliant and features NiPdAu (NIPDAU) lead finish, qualified for lead-free reflow soldering per JEDEC J-STD-020. Its PDIP package has no MSL rating (N/A for Pkg Type), meaning it is not moisture-sensitive and does not require dry-pack or baking prior to assembly - simplifying manufacturing handling compared to fine-pitch surface-mount devices.