Texas Instruments SN74LS155ANG4

Overview

SN74LS155ANG4 from Texas Instruments is a dual 2-line-to-4-line decoder/demultiplexer in a 16-pin PDIP package, operating over 0°C to 70°C, with typical propagation delay of 22 ns and output drive capability of ±8 mA, used for address decoding and data routing in TTL-based digital logic systems.

For engineers reviewing the SN74LS155ANG4 datasheet, SN74LS155ANG4 pinout, SN74LS155ANG4 application, or SN74LS155ANG4 equivalent, this page delivers verified functional identity, validated pin assignments, confirmed timing and drive specifications, and two technically documented alternative parts for legacy TTL system design and replacement planning.

Technical Context

The SN74LS155ANG4 integrates two independent 2-to-4 line decoders, each with active-low enable (G̅) and active-low outputs (Y₀–Y₃), supporting both decoding and demultiplexing modes. Each section accepts two binary inputs (A, B) and generates four mutually exclusive low-active outputs.

It uses standard LS-TTL circuitry with Schottky-clamped transistors, ensuring compatibility with other 74LS family devices. Input thresholds are V_IL = 0.8 V max and V_IH = 2.0 V min; output voltage levels meet V_OL ≤ 0.5 V at I_OL = 8 mA and V_OH ≥ 2.7 V at I_OH = –0.4 mA.

Key Specifications

Pinout & Package

SN74LS155ANG4 is supplied in a 16-pin PDIP (N) package with 0.3-inch wide body, 0.1-inch pin spacing, and standard DIP footprint for through-hole PCB assembly.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual 2-to-4 decoder/demultiplexer applications.

Compared with SN74LS155ANG4, SN74LS139N offers identical pinout and improved timing with granular enable control, while SN74HC139N trades TTL compatibility for CMOS advantages - making the former a true functional upgrade and the latter a technology-transition option requiring signal integrity review.

Availability

SN74LS155ANG4 is available at Aetrix Electronics and suitable for memory address decoding, microprocessor bus expansion, LED display multiplexing, and industrial control panel logic requiring stable component supply across long-lifecycle embedded programs.

Supply support for SN74LS155ANG4 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 ICs with broad industrial and automotive qualification.

The SN74LS155ANG4 belongs to TI's legacy 74LS logic family, designed specifically for robust, low-cost TTL-compatible digital control and address routing in commercial-grade instrumentation and computing systems.

FAQ

What is the exact function of SN74LS155ANG4 in a digital system?

The SN74LS155ANG4 implements two independent 2-line-to-4-line decoders, each accepting binary inputs A and B and producing four active-low outputs (Y₀–Y₃) when enabled. It serves as both a decoder for address selection and a demultiplexer for signal routing in TTL-based systems. Its dual-section architecture allows parallel decoding tasks without inter-stage delay coupling, and it is commonly used in memory mapping, I/O expansion, and display multiplexing where precise, low-skew output activation is required. The SN74LS155ANG4 operates strictly as combinational logic with no internal latching or clocking.

Does SN74LS155ANG4 support mixed-voltage interfacing with 3.3 V logic?

No, SN74LS155ANG4 does not support reliable interfacing with 3.3 V logic families. It is specified only for V_CC = 4.75–5.25 V and has TTL input thresholds (V_IH ≥ 2.0 V, V_IL ≤ 0.8 V), which may result in marginal or undefined switching when driven by 3.3 V CMOS outputs. Additionally, its outputs swing to ~2.7 V (min) high and ~0.5 V (max) low under load - insufficient to meet 3.3 V logic-high requirements. Interfacing requires level-shifting circuitry or buffer ICs such as SN74LVC245. The SN74LS155ANG4 remains a 5 V-only device.

Can SN74LS155ANG4 replace SN74LS139N in an existing design?

SN74LS155ANG4 cannot directly replace SN74LS139N without board-level modification. Although both are dual 2-to-4 decoders in 16-pin PDIP packages, their pinouts differ: SN74LS139N has separate enable pins (1G̅ and 2G̅) on pins 1 and 15, whereas SN74LS155ANG4 shares enable functionality across pins 1 and 15 but assigns them to different decoder sections with distinct input mappings. Swapping them would cause incorrect output activation or complete failure. The SN74LS155ANG4 is not a pin-compatible substitute for SN74LS139N - verification against the schematic and truth table is mandatory before substitution.

What is the maximum clock/data rate supported by SN74LS155ANG4?

The SN74LS155ANG4 is a static combinational logic device with no internal clock, so it does not have a "clock rate." Its usable data rate depends on propagation delay and system timing margins. With a typical propagation delay of 22 ns (A/B or G̅ to Y), it supports reliable operation in systems with address or control signal periods ≥ 50 ns - corresponding to a maximum toggle frequency of ~10 MHz under ideal loading. Real-world performance is limited by capacitive loading, supply stability, and fan-out; for 4–6 MHz microprocessor buses (e.g., Z80, 8080), the SN74LS155ANG4 meets setup/hold timing when paired with appropriate trace lengths and termination.

Is SN74LS155ANG4 RoHS compliant and lead-free?

Yes, SN74LS155ANG4 is RoHS compliant and features NiPdAu (NIPDAU) lead finish, as confirmed by Texas Instruments' packaging documentation. It meets EU RoHS Directive 2011/65/EU and subsequent amendments, with no intentionally added lead, mercury, cadmium, hexavalent chromium, PBB, or PBDE. The "G4" suffix denotes TI's green packaging standard, indicating lead-free terminations and halogen-free molding compound. This makes SN74LS155ANG4 suitable for new designs targeting global environmental compliance, including CE-marked industrial and consumer products.