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Texas Instruments SN74LS155AN
- Part No.:
- SN74LS155AN
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74LS155AN.pdf
- Description:
- IC DECODER/DEMUX 1X2:4 16DIP
- Quantity:
- Payment:
- Shipping:
Inventory:338
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Product details
Overview
SN74LS155AN 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 TTL-compatible inputs and outputs, 16 mA output drive capability, and propagation delay of 22 ns typical at VCC = 5 V. It enables address decoding and data routing in legacy digital logic systems such as industrial control panels and retro-computing peripheral interfaces.
For engineers reviewing the SN74LS155AN datasheet, SN74LS155AN pinout, SN74LS155AN application, or SN74LS155AN equivalent, this page delivers verified functional identity, confirmed pin assignments, real-world timing and drive specifications, and validated drop-in alternatives for legacy system maintenance and redesign.
Technical Context
The SN74LS155AN integrates two independent 2-to-4 line decoders on a single die, each with active-low enable (G̅) and active-low outputs (Y0–Y3). Each decoder accepts two binary inputs (A, B) and generates four mutually exclusive low-active outputs based on input state.
It uses standard TTL bipolar transistor-transistor logic with Schottky clamping, ensuring compatibility with 74LS family voltage thresholds and noise margins. Input clamp diodes provide ESD protection, and output stages support wired-OR configurations via open-collector-like behavior under load.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | 74LS TTL - ensures interoperability with legacy 74LS/74S systems and defined VIH/VIL thresholds. |
| Propagation Delay | 22 ns max (tPLH/tPHL) - determines maximum clock rate for synchronous decode paths in control logic. |
| Output Drive | 16 mA sink per output - supports direct LED driving or fan-out to ≥20 74LS inputs without buffering. |
| Supply Voltage | 4.75 V to 5.25 V - requires regulated +5 V rail; not tolerant of wider ranges or 3.3 V operation. |
| Operating Temperature | 0°C to +70°C - qualified for commercial-grade applications, excluding extended industrial or military environments. |
| Package Type | PDIP-16 (N) - through-hole mounting compatible with prototyping boards and legacy PCBs using 0.1" pitch layouts. |
Pinout & Package
SN74LS155AN is housed in a 16-pin plastic dual in-line package (PDIP), 0.3" wide, with 0.1" lead pitch and standard DIP footprint. Pin 1 is marked by a notch or dot at the top-left corner when viewed from the top with pins facing downward.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | G̅1 (Enable 1) | Active-low enable for Decoder 1; all outputs Y0–Y3 go high when G̅1 = HIGH. |
| 2 | A1 | MSB input for Decoder 1; selects output line in conjunction with B1. |
| 3 | B1 | LSB input for Decoder 1; completes 2-bit address for Y0–Y3 selection. |
| 4–7 | Y01–Y31 | Active-low decoded outputs for Decoder 1; only one low per valid A1B1 combination. |
| 8 | GND | Power ground reference for all internal circuitry and I/O. |
| 9–12 | Y02–Y32 | Active-low decoded outputs for Decoder 2; functionally identical to Y01–Y31. |
| 13 | B2 | LSB input for Decoder 2; pairs with A2 (Pin 15) for second decode path. |
| 14 | VCC | +5 V supply input; must be decoupled locally with 0.1 µF ceramic capacitor. |
| 15 | A2 | MSB input for Decoder 2; completes 2-bit address for Y02–Y32 selection. |
| 16 | G̅2 (Enable 2) | Active-low enable for Decoder 2; independent control allows time-multiplexed or conditional decoding. |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent decoders | Two fully isolated 2-to-4 decode blocks share only VCC and GND, enabling parallel address expansion without inter-stage coupling. |
| Active-low outputs with TTL drive strength | Outputs sink 16 mA while maintaining VOL ≤ 0.5 V, allowing direct interface to LEDs, relays, or other 74LS inputs without pull-up resistors. |
| Separate active-low enables | G̅1 and G̅2 allow asynchronous gating of each decoder-critical for memory chip select arbitration or multiplexed bus control. |
| Standard 74LS AC/DC characteristics | Guaranteed VIH ≥ 2.0 V, VIL ≤ 0.8 V, and IOH/IOL specs ensure plug-and-play replacement in existing 74LS-based designs. |
Applications
| Memory Address Decoding | Peripheral Select Logic |
|---|---|
|
Use Scenario: Selecting one of four RAM or ROM chips in an 8-bit microprocessor system using upper address bits A1 and A0. IC Role / Device Role / Timing Role: SN74LS155AN acts as a 2-bit address decoder, asserting individual chip-select lines with sub-25 ns latency to meet 8080/6502 memory access timing. Use Value: Eliminates need for discrete NAND gate arrays; reduces board space and propagation skew across multiple chip-select paths. |
Use Scenario: Routing serial data between UART, parallel printer port, and floppy controller in a vintage PC-style backplane. IC Role / Device Role / Timing Role: SN74LS155AN functions as a demultiplexer, steering CPU write strobes to one of four peripheral registers based on address lines. Use Value: Enables single-bus architecture with deterministic 22 ns decode delay, avoiding timing race conditions during I/O cycle setup. |
| LED Display Multiplexing | Industrial I/O Expansion |
|
Use Scenario: Driving common-cathode 7-segment displays in a 4-digit multiplexed configuration using segment drivers and digit selects. IC Role / Device Role / Timing Role: SN74LS155AN provides digit-select signals (Y0–Y3) synchronized with display refresh timing, with outputs directly sinking LED current. Use Value: Leverages 16 mA output drive to eliminate external transistors; simplifies BOM and improves reliability in panel-mounted instrumentation. |
Use Scenario: Expanding discrete input/output points in a PLC rack where main controller has limited native I/O pins. IC Role / Device Role / Timing Role: SN74LS155AN decodes command bus bits to activate one of four relay driver modules or sensor conditioning circuits. Use Value: Provides deterministic, glitch-free selection with TTL noise immunity-critical for safety-critical on/off control in factory automation. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar dual 2-to-4 decoder applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS139N | Identical pinout and function but includes dual enable (G̅1, G̅2) shared across both decoders; no separate A/B per decoder. | Requires modified enable logic if independent decoder gating is needed; better suited for synchronous enable scenarios. | Select SN74LS139N only when both decoders must be enabled/disabled together-reduces external logic count. |
| SN74HC139N | CMOS version with 2–6 V supply range, 12 ns propagation delay, and 4 mA output drive; incompatible TTL input thresholds. | Not directly interchangeable without level-shifting; suitable only in new 3.3 V or mixed-voltage designs with updated I/O design. | Choose SN74HC139N for lower power and higher speed in non-legacy systems-but verify VIH/VIL compatibility before substitution. |
Compared with SN74LS155AN, SN74LS139N offers tighter enable coordination at the cost of decoder independence, while SN74HC139N delivers speed and voltage flexibility but requires full signal-level redesign-not drop-in replacement.
Availability
SN74LS155AN is available at Aetrix Electronics and suitable for industrial control panels, retro-computing restoration projects, and legacy test equipment requiring stable component supply with long-term obsolescence mitigation.
Supply support for SN74LS155AN 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 SN74LS155AN belongs to TI's legacy 74LS logic family, designed specifically for reliable, noise-immune digital control in commercial-grade systems built before the mid-1990s.
FAQ
What is the maximum clock frequency supported by SN74LS155AN?
The SN74LS155AN is not a clocked device-it operates combinatorially with no internal clock. Its usable switching rate depends on propagation delay (22 ns typical) and system setup/hold timing. In practice, it reliably supports address decode cycles up to ~20 MHz in well-designed 74LS-based buses, assuming clean edges and proper termination. The SN74LS155AN does not specify a clock frequency because it lacks sequential elements.
Can SN74LS155AN drive LEDs directly without current-limiting resistors?
No-SN74LS155AN outputs must always be used with series current-limiting resistors. While its 16 mA sink capability supports common indicator LEDs, exceeding VOL ≤ 0.5 V or violating IOL limits risks output degradation. For a typical red LED (VF ≈ 1.8 V at 10 mA), a 330 Ω resistor is required with VCC = 5 V. Direct connection without resistance will overstress the SN74LS155AN output stage.
Is SN74LS155AN pin-compatible with SN74LS139N?
No-SN74LS155AN and SN74LS139N have different pinouts. SN74LS155AN assigns separate A/B inputs per decoder (Pins 2/3 and 13/15), while SN74LS139N shares A/B across both decoders (Pins 1/2). Their enable structures also differ: SN74LS155AN has independent G̅1/G̅2 (Pins 1/16), whereas SN74LS139N uses a single dual-enable input (Pin 1). PCB layout changes are required for substitution.
Does SN74LS155AN support 3.3 V operation?
No-SN74LS155AN is strictly a 5 V TTL device. Its input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V) and output drive characteristics are specified only for VCC = 4.75–5.25 V. Operation at 3.3 V results in undefined logic states, excessive input current, and failure to meet VOL/VOH specs. For 3.3 V systems, consider SN74HC139N instead-but note it is not pin-compatible with SN74LS155AN.
What is the meaning of the "N" suffix in SN74LS155AN?
The "N" suffix in SN74LS155AN denotes the plastic dual in-line package (PDIP) variant, per Texas Instruments' standard packaging nomenclature. It confirms the device uses a 16-pin through-hole PDIP-16 body with 0.3" width and 0.1" lead pitch. This distinguishes it from SOIC (D), SOP (NS), CDIP (J), or CFP (W) variants-each with different mechanical, thermal, and assembly requirements. The SN74LS155AN is the standard through-hole version for breadboarding and legacy repair.
SN74LS155AN Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 16-DIP (0.300", 7.62mm)
- Packaging:
- Bulk
- Product Status:
- Active
- Type:
- Decoder/Demultiplexer
- Circuit:
- 1 x 2:4
- Independent Circuits:
- 2
- Current - Output High, Low:
- 400µA, 8mA
- Voltage Supply Source:
- Single Supply
- Voltage - Supply:
- 4.75V ~ 5.25V
- Operating Temperature:
- 0°C ~ 70°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 16-PDIP
SN74LS155AN FAQ
1.How can I place an order for SN74LS155AN through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS155AN on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for SN74LS155AN reliable?
The price and inventory of SN74LS155AN are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS155AN is usually 5 days.
3.What payment methods are accepted for SN74LS155AN?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS155AN transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS155AN?
SN74LS155AN orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS155AN order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for SN74LS155AN?
For technical support, including SN74LS155AN datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS155AN requirements.
6.How does Aetrix verify that SN74LS155AN is sourced from the original manufacturer or authorized distributors?
All SN74LS155AN products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that SN74LS155AN meets industry standards.
7.What is the process for return or replacement of SN74LS155AN?
All SN74LS155AN units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS155AN, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The SN74LS155AN part is unused and in its original packaging.
Return procedure for SN74LS155AN:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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