Texas Instruments SN74LS51DR

Overview

SN74LS51DR from Texas Instruments is a dual 2-input AND-OR-INVERT (AOI) logic gate IC in SOIC-14 package, operating at 0°C to 70°C, with typical propagation delay of 15 ns at V_CC = 5 V and fan-out of 20 LS-TTL loads. It implements two independent AOI functions: (A·B)+(C·D) → Y̅, used for combinational logic reduction in industrial control sequencers and legacy TTL system glue logic.

For engineers reviewing the SN74LS51DR datasheet, SN74LS51DR pinout, SN74LS51DR application, or SN74LS51DR equivalent, key selection considerations include its LS-TTL-compatible input thresholds, 15 ns propagation delay, SOIC-14 RoHS-compliant packaging, and direct compatibility with SN74LS00-series logic families in mixed-logic-level designs.

Technical Context

The SN74LS51DR integrates two identical AND-OR-INVERT gates on a single die, each accepting two 2-input AND terms whose outputs feed a wired-OR node driving a common inverting output stage. Its bipolar transistor–transistor logic (TTL) architecture ensures stable operation under ±0.4 V input noise margin and supports standard TTL drive capability.

Designed for direct interface with other LS-TTL devices, it features active-low open-collector compatible outputs when used with external pull-ups, and maintains guaranteed high/low output voltage levels (V_OH ≥ 2.7 V, V_OL ≤ 0.5 V) across full temperature and supply ranges.

Key Specifications

Pinout & Package

SN74LS51DR uses a 14-pin Small Outline Integrated Circuit (SOIC) package with 1.27 mm pitch, 3.9 mm body width, and 1.75 mm max height per JEDEC MS-012AB. Pin 1 is marked by a beveled corner or laser dot; device orientation follows standard Q1 quadrant tape-and-reel placement.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar AND-OR-INVERT logic applications.

Compared with SN74LS00DR and SN74LS54DR, the SN74LS51DR delivers optimal gate efficiency and timing predictability for dual, independent (A·B)+(C·D) logic-reducing layout area and eliminating synthesis overhead in fixed-function TTL systems.

Availability

SN74LS51DR is available at Aetrix Electronics and suitable for industrial control sequencers, legacy system bus interfaces, test equipment signal routing, automated test fixture logic, and commercial-grade embedded controller designs requiring stable component supply over extended production lifecycles.

Supply support for SN74LS51DR 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and consumer markets.

The SN74LS51DR belongs to TI's legacy 74LS logic family, designed specifically to replace standard TTL with lower power consumption and improved speed while maintaining full pin and functional compatibility across commercial temperature ranges.

FAQ

What logic function does the SN74LS51DR implement?

The SN74LS51DR implements two independent AND-OR-INVERT (AOI) functions: each accepts four inputs arranged as two 2-input AND gates whose outputs feed an OR gate, followed by an inverter. The resulting expression is Y = ((A·B)+(C·D))′. This structure is documented in TI's SDLS113 datasheet and enables compact realization of sum-of-products logic without external inversion stages. The SN74LS51DR is optimized for this exact function-not generic gate arrays or programmable logic.

Is SN74LS51DR pin-compatible with SN74LS00 or SN74LS04?

No, SN74LS51DR is not pin-compatible with SN74LS00 (quad NAND) or SN74LS04 (hex inverter). It uses a unique 14-pin SOIC pinout with eight inputs (pins 1,2,4,5,8,9,11,12), two outputs (pins 3,10), V_CC (pin 14), and GND (pin 7). While functionally related through Boolean algebra, direct substitution would require PCB redesign. The SN74LS51DR pinout is fixed per TI's D0014A package drawing and cannot be adapted to other 74LS footprints.

Can SN74LS51DR drive LEDs directly?

Yes, SN74LS51DR outputs are open-collector and can sink up to 8 mA per output (I_OL = 8 mA min at V_OL = 0.5 V), sufficient to drive standard 2 mA LEDs with appropriate series resistors (e.g., 470 Ω from +5 V). However, it cannot source current-LED anodes must connect to V_CC, cathodes to SN74LS51DR outputs. This behavior is specified in the "Electrical Characteristics" table of SDLS113 and applies identically to SN74LS51DR.

Does SN74LS51DR support mixed-voltage interfacing (e.g., 3.3 V logic)?

SN74LS51DR inputs accept 3.3 V CMOS logic levels (V_IH = 2.0 V min), making them compatible with 3.3 V microcontrollers when driven actively. However, its outputs swing to near 0 V or float (open-collector), so interfacing with 3.3 V receivers requires a pull-up resistor to 3.3 V-not 5 V-to avoid overstressing inputs. This configuration is validated in TI application note SCBA005 and confirmed for SN74LS51DR in commercial temperature range operation.

What is the maximum clock frequency achievable using SN74LS51DR in a feedback oscillator?

SN74LS51DR is not designed for oscillator use. Its propagation delay (15 ns typ) and lack of hysteresis or controlled slew rate make it unsuitable for reliable ring oscillators. TI explicitly specifies the device for combinational logic only; no AC characterization or stability data exists for oscillatory configurations. For timing applications, dedicated clock generators or 555-based circuits are recommended instead of repurposing SN74LS51DR.