Texas Instruments SN74LS155ANSR

Overview

SN74LS155ANSR from Texas Instruments is a dual 2-line-to-4-line decoder/demultiplexer in SOP-16 package, operating over 0°C to 70°C, with typical propagation delay of 22 ns at V_CC = 5 V and I_OL = 8 mA, used for address decoding and data routing in TTL-compatible digital systems.

For engineers reviewing the SN74LS155ANSR datasheet, SN74LS155ANSR pinout, SN74LS155ANSR application, or SN74LS155ANSR equivalent, key selection factors include its dual independent decode logic, active-low enable control (G̅), complementary active-low outputs (Y̅₀–Y̅₃), TTL input thresholds, and compatibility with legacy 74LS logic families in industrial control and instrumentation designs.

Technical Context

The SN74LS155ANSR integrates two identical 2-to-4 line decoders on a single die, each with separate address inputs (A, B), individual active-low strobe (G̅), and four active-low decoded outputs (Y̅₀–Y̅₃). No shared logic or internal interconnect exists between the two sections.

Each decoder implements standard binary decoding: when G̅ = LOW, outputs reflect Y̅_i = (A B)_i̅; when G̅ = HIGH, all outputs remain HIGH regardless of A/B states. Input thresholds match standard LS-TTL (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V), and output drive capability is rated at I_OH = –0.4 mA / I_OL = 8 mA.

Key Specifications

Pinout & Package

SOP-16 (NS) package: 16-pin small-outline plastic package with gull-wing leads, 1.27 mm pitch, 10.4 mm × 5.3 mm body size, maximum height 2.00 mm, pin 1 marked by beveled corner or notch.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS155ANSR, SN74LS139DR offers unified enable control ideal for power-gated subsystems, while SN74HC139PWR trades TTL compatibility for lower power and voltage flexibility - neither is pin-compatible without circuit modification, and both require careful evaluation of enable structure and logic family interoperability.

Availability

SN74LS155ANSR is available at Aetrix Electronics and suitable for memory address decoding, peripheral select logic, LED display multiplexing, and legacy system bus expansion requiring stable component supply and long-term industrial availability.

Supply support for SN74LS155ANSR 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 products with broad industrial and automotive qualification.

The SN74LS155ANSR belongs to TI's legacy 74LS logic family, designed specifically for TTL-compatible digital systems requiring predictable timing, robust noise immunity, and backward compatibility with 1970s–1990s digital architectures.

FAQ

What is the maximum clock frequency supported by SN74LS155ANSR?

The SN74LS155ANSR is not a clocked device and has no maximum clock frequency specification. It is a combinational logic decoder with propagation delay of 22 ns typical. Its usable switching rate depends on system-level timing constraints, including setup/hold times of driven devices and board trace delays - not an internal clock domain.

Can SN74LS155ANSR drive LEDs directly without current-limiting resistors?

No. While SN74LS155ANSR outputs can sink up to 8 mA, direct LED connection without a series resistor risks exceeding absolute maximum ratings under varying V_F and temperature. A minimum 330 Ω resistor is required for standard 2 V red LEDs at 5 V supply to limit current to ~9 mA - always use external current limiting per output.

Is SN74LS155ANSR pin-compatible with SN74LS139?

No. SN74LS155ANSR and SN74LS139 have different pin assignments: SN74LS155ANSR uses separate G̅ enables per section (pins 1 and 15), while SN74LS139 uses shared 1E̅/2E̅ enables (pins 1 and 15). Output pin locations also differ. Physical replacement requires PCB redesign.

Does SN74LS155ANSR support mixed-voltage operation (e.g., 3.3 V inputs)?

No. SN74LS155ANSR is strictly a 5 V TTL device. Its input thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V) are incompatible with 3.3 V logic levels - 3.3 V high signals may not register reliably as HIGH, causing undefined outputs. Use level translators or a 74LVC-series alternative for 3.3 V systems.

What is the recommended bypass capacitor value for SN74LS155ANSR?

A 0.1 µF ceramic capacitor placed as close as possible to pins 16 (V_CC) and 8 (GND) is mandatory for stable operation. For boards with multiple SN74LS155ANSR devices or high switching activity, add a bulk 4.7 µF–10 µF tantalum or aluminum electrolytic capacitor per power rail segment to suppress low-frequency supply droop.