Texas Instruments CD74HC251EG4

Overview

CD74HC251EG4 from Texas Instruments is an 8-input, three-state digital multiplexer with true (Y) and complement (Y̅) outputs, operating across 2 V to 6 V supply range. It delivers 14 ns typical propagation delay (V_CC = 5 V, C_L = 15 pF), supports –55 °C to 125 °C industrial/military temperature range, and drives up to 10 LSTTL loads - used in bus-oriented data routing, address selection, and signal gating in embedded control systems.

For engineers reviewing the CD74HC251EG4 datasheet, CD74HC251EG4 pinout, CD74HC251EG4 application, or CD74HC251EG4 equivalent, this page provides verified functional identity, validated pin-level behavior, confirmed electrical specs at temperature extremes, and real-world substitution guidance for logic multiplexer selection in high-reliability digital systems.

Technical Context

The CD74HC251EG4 implements a silicon-gate CMOS 8:1 multiplexer with independent enable-controlled three-state outputs, supporting simultaneous true and inverted output delivery. Its select inputs (S0–S2) decode binary addresses to route one of eight data inputs (I0–I7) to Y/Y̅, while OE must be low to activate outputs - high OE forces both outputs into high-impedance state.

It complies with HC logic family specifications: VIH/VIL thresholds scale with V_CC (e.g., VIH = 3.15 V min at 4.5 V), input leakage ≤ ±1 µA, and ICC ≤ 160 µA over full temperature range. Propagation delays are characterized separately for data-to-output (12 ns typ at 5 V), select-to-output (18 ns typ), and enable-to-Z transitions (12 ns typ).

Key Specifications

Pinout & Package

CD74HC251EG4 is supplied in 16-pin PDIP (plastic dual in-line package) with 19.31 mm × 6.35 mm body size and through-hole mounting compatibility.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 8-input multiplexer applications.

Compared with SN74HC251N, CD74HC251EG4 offers extended temperature resilience critical for harsh environments; versus CD74HCT251E, it trades TTL input compatibility for higher noise immunity and broader V_CC flexibility - enabling direct use with 3.3 V microcontrollers without level translation.

Availability

CD74HC251EG4 is available at Aetrix Electronics and suitable for industrial PLC I/O modules, automotive ECU sensor interfaces, and legacy bus adapter designs requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HC251EG4 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 ICs, with decades of heritage in high-reliability logic families.

The CD74HC251EG4 belongs to TI's CD74HC high-speed CMOS logic series, engineered for robust performance in military, aerospace, and industrial systems where wide temperature operation and noise immunity are mandatory.

FAQ

What is the maximum supply voltage for CD74HC251EG4?

The absolute maximum supply voltage for CD74HC251EG4 is 7 V, but the recommended operating range is 2 V to 6 V. Operation above 6 V risks permanent damage, while below 2 V may cause unreliable logic thresholds or increased propagation delay. The device achieves optimal noise immunity and speed at 4.5 V to 5.5 V, and remains fully functional down to 2 V for ultra-low-power applications. Always observe the 0.1 µF bypass capacitor requirement at V_CC regardless of supply voltage.

Does CD74HC251EG4 support true and complement outputs simultaneously?

Yes, CD74HC251EG4 provides both true (Y) and complement (Y̅) outputs simultaneously - they reflect the same selected input but with opposite logic polarity. Both outputs share identical timing characteristics (12 ns typical propagation delay at 5 V), drive strength (10 LSTTL loads), and three-state control via the single OE pin. This dual-output architecture eliminates the need for external inverters in applications requiring differential signaling, parity generation, or redundant path verification.

Can CD74HC251EG4 interface directly with TTL logic inputs?

No, CD74HC251EG4 is not TTL-input-compatible - its VIH and VIL thresholds scale with V_CC (e.g., VIH ≥ 3.15 V at 4.5 V), unlike TTL's fixed 2 V/0.8 V thresholds. Direct connection to standard 74LS outputs may result in marginal or failed logic recognition. For TTL interface, use the pin-compatible CD74HCT251E instead. If interfacing CD74HC251EG4 with TTL, a level-shifting buffer or resistor-divider network is required to meet HC input voltage specifications.

What is the purpose of the OE pin on CD74HC251EG4?

The OE (Output Enable) pin on CD74HC251EG4 is an active-low control that enables or disables both Y and Y̅ outputs. When OE = low, the selected input appears at Y/Y̅ with full drive capability. When OE = high, both outputs enter high-impedance (three-state) mode, drawing ≤ ±10 µA leakage current - essential for bus sharing and preventing signal contention. OE timing is characterized separately: enable-to-output delay is 12 ns typical, disable-to-high-Z is also 12 ns typical at 5 V.

Is CD74HC251EG4 RoHS compliant?

Yes, CD74HC251EG4 is RoHS compliant, as confirmed by Texas Instruments' packaging documentation. It uses NiPdAu (NIPDAU) lead finish and meets EU Directive 2011/65/EU requirements. The "G4" suffix in the part number specifically denotes RoHS-compliant packaging per TI's ordering nomenclature. No lead or other restricted substances exceed allowable thresholds, and the device is suitable for use in consumer, industrial, and medical electronics subject to RoHS enforcement.