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Texas Instruments SN74LS155AD
- Part No.:
- SN74LS155AD
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
SN74LS155AD.pdf
- Description:
- IC DECODER/DEMUX 1X2:4 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:188
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Product details
Overview
SN74LS155AD from Texas Instruments is a dual 2-line-to-4-line decoder/demultiplexer in a 16-pin SOIC package, operating over 0°C to 70°C, with TTL-compatible inputs and outputs, propagation delay of 22 ns (typ), and supply current of 24 mA (max) at VCC = 5 V. It enables address decoding in 8-bit microprocessor systems and channel selection in data routing applications.
For engineers reviewing the SN74LS155AD datasheet, SN74LS155AD pinout, SN74LS155AD application, or SN74LS155AD equivalent, key selection criteria include dual independent enable-controlled decoding paths, TTL-level compatibility, 16-pin SOIC footprint, guaranteed fan-out of 20 LS-TTL loads, and legacy industrial control system integration requirements.
Technical Context
The SN74LS155AD implements two identical 2-to-4 line decoders, each with separate active-low enable (G̅) and complementary address inputs (A₀, A₁). Each decoder drives four open-collector outputs (Y₀–Y₃), supporting wired-OR logic and level translation via external pull-ups.
It uses bipolar Schottky TTL technology, delivering consistent timing across temperature (22 ns max tpd), defined input thresholds (VIL = 0.8 V, VIH = 2.0 V), and output drive capability (IOL = 8 mA, IOH = –0.4 mA) suitable for direct interface with LS-TTL and standard TTL loads.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | Dual 2-line-to-4-line decoder/demultiplexer with independent enables |
| Logic Family | LS-TTL - ensures compatibility with legacy 74LS series and predictable noise margins |
| Propagation Delay | 22 ns (max) - supports reliable operation up to ~20 MHz clocked enable/address transitions |
| Supply Voltage | 4.75 V to 5.25 V - requires regulated 5 V rail; no wide-VCC flexibility |
| Output Type | Open-collector - enables wired-OR bus structures and mixed-voltage interfacing with pull-up resistors |
| Fan-out | 20 LS-TTL loads - sufficient to drive multiple downstream gates without buffering |
| Operating Temperature | 0°C to 70°C - commercial-grade rating; not qualified for extended or military environments |
Pinout & Package
SN74LS155AD is housed in a 16-pin Small Outline Integrated Circuit (SOIC) package (Package Code D), 7.5 mm wide, with 1.27 mm pitch, RoHS-compliant NiPdAu lead finish, and moisture sensitivity level 1 (260°C peak reflow).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 15 | Enable (G̅₁, G̅₂) | Active-low enable per decoder; both must be low for corresponding outputs to respond to address inputs |
| 2, 3, 5, 6 | Address Inputs (A₀₁, A₁₁, A₀₂, A₁₂) | Complementary pairs per decoder; A₀/A₁ select one of four active-low outputs (Y₀–Y₃) |
| 4, 7, 9, 10, 12, 13 | Outputs (Y₀₁–Y₃₁, Y₀₂–Y₃₂) | Open-collector; sink current only; require external pull-up for HIGH state |
| 8 | GND | Ground reference for all internal circuitry and output sinks |
| 16 | VCC | +5 V power supply; bypassing with 0.1 µF ceramic capacitor near pin recommended |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent decoders | Enables simultaneous decoding of two 2-bit address buses without shared control logic |
| Open-collector outputs | Supports bus arbitration, level shifting, and wired-OR sum-of-products logic implementation |
| TTL-compatible thresholds | VIL ≤ 0.8 V and VIH ≥ 2.0 V ensure robust noise immunity in noisy industrial backplanes |
| Guaranteed AC/DC specs | Full parametric testing per SDLS057 (1988 rev) ensures timing consistency across production lots |
| SOIC packaging | Surface-mount 16-pin footprint reduces PCB area vs. PDIP; compatible with automated assembly |
Applications
| Microprocessor Address Decoding | Industrial I/O Multiplexing |
|---|---|
Use Scenario: Selecting peripheral devices (e.g., UART, timer, RAM) in an 8080/8085-based control system using 2-bit address lines. IC Role / Device Role / Timing Role: Decoder translating CPU address bits into individual chip-select signals with deterministic 22 ns latency. Use Value: Eliminates discrete gate logic for 4-device decode; maintains timing predictability across temperature and voltage. | Use Scenario: Routing sensor data streams from four analog input channels to a single ADC in PLC analog modules. IC Role / Device Role / Timing Role: Demultiplexer enabling time-shared sampling under microcontroller control via enable and address lines. Use Value: Reduces component count vs. analog switches; leverages existing TTL control signals without level-shifting. |
| Legacy Bus Arbitration | Wired-OR Logic Generation |
Use Scenario: Managing interrupt request lines from multiple peripherals onto a shared INT line in vintage computer designs. IC Role / Device Role / Timing Role: Active-low open-collector outputs allow multiple SN74LS155AD units to drive one bus line without contention. Use Value: Enables priority-encoded interrupt handling using external pull-up and resistor networks. | Use Scenario: Implementing sum-of-products logic (e.g., enable conditions for motor drivers) in safety-critical relay panels. IC Role / Device Role / Timing Role: Each decoder output represents a minterm; wired-OR combines terms without additional gates. Use Value: Provides field-modifiable logic via jumpered pull-ups - no FPGA or CPLD required. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar dual decoder/demultiplexer applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS155AN | Same logic function and AC/DC specs, but in 16-pin PDIP (N) package with through-hole mounting | Suitable for prototyping, repair, or legacy through-hole PCBs; lacks SOIC thermal and density advantages | Select SN74LS155AN for hand-soldered development or replacement on existing DIP layouts. |
| SN74LS155ADR | Identical electrical specs and SOIC (D) package, but supplied in 2500-piece tape-and-reel (active status vs. obsolete SN74LS155AD) | Designed for high-volume SMT production; same footprint and solder profile as SN74LS155AD | Choose SN74LS155ADR for new designs requiring assured supply continuity and automated assembly support. |
Compared with SN74LS155AD, SN74LS155AN offers through-hole reliability for serviceable systems, while SN74LS155ADR provides identical performance with guaranteed long-term availability and optimized logistics for SMT manufacturing - neither is pin-compatible with non-SOIC variants, and all share identical truth tables and timing behavior.
Availability
SN74LS155AD is available at Aetrix Electronics and suitable for microprocessor address decoding, industrial I/O multiplexing, legacy bus arbitration, and wired-OR logic generation requiring stable component supply in commercial-temperature embedded systems.
Supply support for SN74LS155AD 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, automotive, and consumer reach.
The SN74LS155AD belongs to TI's legacy 74LS logic family, designed specifically for TTL-compatible digital systems requiring deterministic timing, robust noise margins, and drop-in replacement capability in established 5 V control architectures.
FAQ
What is the maximum clock frequency supported by SN74LS155AD?
The SN74LS155AD is not a clocked device - it is a combinational decoder/demultiplexer with no internal clock. Its usable switching rate depends on input transition speed and propagation delay: with tpd = 22 ns (max), it reliably supports address/data changes up to approximately 20 MHz in well-terminated 5 V TTL systems. System-level timing must account for setup/hold times of driving sources and load capacitance.
Does SN74LS155AD support 3.3 V logic interfaces?
No, SN74LS155AD is strictly a 5 V TTL device. Its input thresholds (VIL = 0.8 V, VIH = 2.0 V) and output voltage levels (VOL ≈ 0.35 V, VOH undefined without pull-up) are specified only for VCC = 4.75–5.25 V. Direct connection to 3.3 V CMOS or LVTTL requires level-shifting circuitry; SN74LS155AD itself does not tolerate 3.3 V supply or guarantee interoperability at that voltage.
Can SN74LS155AD outputs be paralleled for higher current drive?
Yes - because SN74LS155AD features open-collector outputs, multiple outputs (e.g., Y₀₁ and Y₀₂) can be wired together with a single pull-up resistor to implement OR logic or increase sink current capacity. Total sink current must remain within the absolute maximum rating of 8 mA per output and 50 mA total for the device. Do not parallel outputs driven to opposite states.
Is SN74LS155AD still in production?
No - SN74LS155AD is marked "Obsolete" in TI's official packaging documentation. While limited stock may exist, TI no longer manufactures this specific orderable part number. For new designs, TI recommends SN74LS155ADR (active, SOIC, tape-and-reel) or SN74LS155AN (active, PDIP) as functionally identical replacements with full production support.
What is the purpose of the complementary address inputs on SN74LS155AD?
SN74LS155AD does not have complementary address inputs. Pins 2/3 and 5/6 are independent address inputs (A₀₁/A₁₁ and A₀₂/A₁₂) for each decoder - they are not differential or inverted pairs. Each decoder accepts two single-ended TTL-level address bits to select one of four active-low outputs (Y₀–Y₃); inversion must be implemented externally if needed. The device truth table confirms standard binary decoding, not complemented-input operation.
SN74LS155AD Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 16-SOIC (0.154", 3.90mm Width)
- Packaging:
- Bulk
- Product Status:
- Obsolete
- 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:
- Surface Mount
- Supplier Device Package:
- 16-SOIC
SN74LS155AD FAQ
1.How can I place an order for SN74LS155AD through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS155AD 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 SN74LS155AD reliable?
The price and inventory of SN74LS155AD are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS155AD is usually 5 days.
3.What payment methods are accepted for SN74LS155AD?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS155AD transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS155AD?
SN74LS155AD orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS155AD 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 SN74LS155AD?
For technical support, including SN74LS155AD datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS155AD requirements.
6.How does Aetrix verify that SN74LS155AD is sourced from the original manufacturer or authorized distributors?
All SN74LS155AD 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 SN74LS155AD meets industry standards.
7.What is the process for return or replacement of SN74LS155AD?
All SN74LS155AD units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS155AD, 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 SN74LS155AD part is unused and in its original packaging.
Return procedure for SN74LS155AD:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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