Texas Instruments SN74HCT125DT

Overview

SN74HCT125DT from Texas Instruments is a quadruple 3-state bus buffer gate IC with TTL-compatible inputs and high-current outputs, operating at 4.5–5.5 V supply, delivering ±6 mA output drive at 5 V, 12 ns typical propagation delay, and supporting up to 15 LSTTL loads in memory address buffering and data bus isolation applications.

For engineers reviewing the SN74HCT125DT datasheet, SN74HCT125DT pinout, SN74HCT125DT application, or SN74HCT125DT equivalent, key selection criteria include 3-state output timing (ten/tdis ≤35 ns), low ICC (≤80 µA), input voltage compatibility (VIH = 2 V, VIL = 0.8 V), and SOIC-14 package thermal performance (RθJA = 138.7 °C/W).

Technical Context

The SN74HCT125DT implements four independent non-inverting buffers (Y = A) with individual 3-state enable controls (OE), where each output enters high-impedance state when OE is high. Its HCT logic family ensures TTL-level input thresholds while maintaining CMOS power efficiency.

It operates strictly within 4.5–5.5 V supply range, supports 500 ns max input transition time, and requires all unused inputs tied to VCC or GND to prevent floating states - critical for stable bus arbitration in shared-data-path systems.

Key Specifications

Pinout & Package

SN74HCT125DT uses a 14-pin SOIC (D) package with nominal body size 8.65 mm × 3.90 mm and maximum height 1.75 mm, optimized for surface-mount assembly and moderate-power board-level integration.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar bus buffer applications.

Compared with SN74HCT125DT, SN74HCT244N offers double channel density at the cost of larger package and no pin compatibility, while 74LVC125PW provides broader voltage flexibility and higher drive at 3.3 V but demands careful voltage-domain coordination in 5 V-only systems.

Availability

SN74HCT125DT is available at Aetrix Electronics and suitable for memory address buffering, microcontroller bus isolation, legacy system bus expansion, and industrial control backplane interface applications requiring stable component supply and long-term obsolescence management.

Supply support for SN74HCT125DT 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 SN74HCT125DT belongs to TI's 74HCT logic family, designed specifically for TTL-to-CMOS interfacing in 5 V systems requiring low power, high noise immunity, and robust bus-driving capability.

FAQ

What is the operating voltage range for the SN74HCT125DT?

The SN74HCT125DT operates over a supply voltage range of 4.5 V to 5.5 V. This range ensures compatibility with standard 5 V TTL and CMOS logic families while maintaining specified timing and drive performance. Operation outside this range may result in undefined behavior or device damage, as confirmed by absolute maximum ratings in the TI datasheet SCLS069G.

Does the SN74HCT125DT support 3-state outputs, and how are they controlled?

Yes, the SN74HCT125DT features four independent 3-state outputs, each controlled by its own active-low output-enable (OE) input (pins 1, 4, 10, 13). When OE is high, the corresponding Y output enters high-impedance state; when OE is low, the buffer passes A to Y. This architecture enables safe bus sharing without contention, as documented in the function table and pin configuration section of the SN74HCT125DT datasheet.

What is the typical propagation delay of the SN74HCT125DT, and under what conditions is it measured?

The typical propagation delay (tpd) of the SN74HCT125DT is 12 ns, measured at VCC = 5 V, TA = 25°C, and CL = 50 pF. The datasheet specifies a maximum tpd of 22 ns under those same conditions, with worst-case values rising to 48 ns at CL = 150 pF. These values reflect the delay from A or OE input transition to valid Y output transition, critical for timing budgeting in synchronous bus designs.

Can unused inputs on the SN74HCT125DT be left floating?

No, unused inputs on the SN74HCT125DT must not be left floating. TI explicitly requires all unused inputs to be tied to either VCC or GND to prevent undefined logic states, increased power consumption, or oscillation. This requirement is stated in Section 5.2 and reinforced in Layout Guidelines (Section 9.1) of the SN74HCT125DT datasheet due to the HCT family's sensitivity to indeterminate input voltages.

Is the SN74HCT125DT pin-compatible with other packages in the same family, such as SN74HCT125N?

Yes, the SN74HCT125DT (SOIC-14) shares identical pinout and electrical functionality with SN74HCT125N (PDIP-14) and other variants like SN74HCT125DR. All members of the SN74HCT125 family use the same 14-pin functional mapping - including OE, A, Y, VCC, and GND positions - enabling direct PCB footprint substitution between SOIC and PDIP packages where mechanical constraints allow.