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Texas Instruments SN74LS156NSR
- Part No.:
- SN74LS156NSR
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SOIC (0.209", 5.30mm Width)
- Datasheet:
-
SN74LS156NSR.pdf
- Description:
- IC DECODER/DEMUX 2 X 1:4 16SO
- Quantity:
- Payment:
- Shipping:
Inventory:3,114
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Product details
Overview
SN74LS156NSR from Texas Instruments is a dual 2-line-to-4-line decoder/demultiplexer in the 74LS logic family, performing independent address decoding and data routing for two separate 2-bit inputs, with TTL-compatible input thresholds and guaranteed fan-out of 20 LS-TTL loads. It operates over 0°C to 70°C and supports standard 5-V digital systems in legacy industrial control and instrumentation.
For engineers reviewing the SN74LS156NSR datasheet, SN74LS156NSR pinout, SN74LS156NSR application, or SN74LS156NSR equivalent, key selection considerations include its dual-decoder architecture, active-low enable and output logic, SOP-16 package compatibility with surface-mount assembly, and direct functional equivalence within the SN74LS155/156 family.
Technical Context
The SN74LS156NSR integrates two identical 2-to-4 line decoders on a single die, each with two address inputs (A₀, A₁), one active-low enable (/E), and four active-low decoded outputs (/Y₀–/Y₃). Both sections share no internal signal coupling - enabling independent operation for parallel address decoding or dual-channel demux functions.
Each decoder uses standard TTL bipolar transistor-transistor logic with Schottky-clamped outputs, delivering typical propagation delays of 15 ns (max 25 ns) at VCC = 5 V and IOL = 8 mA, while maintaining DC output drive capability of –0.4 mA (high) and 8 mA (low) per output.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | 74LS (Low-power Schottky TTL) - ensures compatibility with legacy 5-V TTL systems and predictable noise margins. |
| Function | Dual 2-line-to-4-line decoder/demultiplexer - provides two independent decode paths without shared control lines. |
| Supply Voltage | VCC = 4.75 V to 5.25 V - strict 5-V operation; not tolerant of wider voltage ranges or 3.3-V interfaces. |
| Propagation Delay | tPD = 15 ns typical (25 ns max) - defines maximum clock/data rate for synchronous address decoding in real-time control logic. |
| Output Drive | IOH = –0.4 mA / IOL = 8 mA - supports direct driving of multiple LS-TTL inputs or small LED indicators without buffering. |
| Operating Temperature | 0°C to +70°C - commercial-grade rating suitable for non-extreme industrial enclosures and benchtop equipment. |
| Package | SOP-16 (NS) - 16-pin small-outline package with 1.27-mm pitch, compatible with standard reflow profiles (MSL Level-1). |
Pinout & Package
SOP-16 (NS) package: 16-pin surface-mount small-outline package, 10.4 mm × 5.3 mm body, 1.27 mm lead pitch, 2.00 mm max height, gull-wing leads, pin 1 marked by beveled corner or dot.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | /E₁ (Enable 1) | Active-low enable for first decoder; when high, all Y₀–Y₃ outputs forced high (inactive). |
| 2 | A₀₁ (Address 0, Decoder 1) | LSB address input for first decoder; determines low-order bit of 2-bit decode address. |
| 3 | A₁₁ (Address 1, Decoder 1) | MSB address input for first decoder; combined with A₀₁ selects one of four outputs. |
| 4–7 | /Y₀₁–/Y₃₁ | Active-low decoded outputs for first decoder; only one asserted low per valid address+enable state. |
| 8 | GND | Ground reference for all logic and output stages; must be low-impedance connection. |
| 9–12 | /Y₀₂–/Y₃₂ | Active-low decoded outputs for second decoder; functionally isolated from first decoder section. |
| 13 | A₁₂ (Address 1, Decoder 2) | MSB address input for second decoder; independent of A₁₁, allowing concurrent but distinct decoding. |
| 14 | A₀₂ (Address 0, Decoder 2) | LSB address input for second decoder; paired with A₁₂ to select /Y₀₂–/Y₃₂ outputs. |
| 15 | /E₂ (Enable 2) | Active-low enable for second decoder; high disables all /Y₀₂–/Y₃₂ outputs regardless of address. |
| 16 | VCC | +5 V supply; bypassing with 0.1 µF ceramic capacitor near pin recommended for noise suppression. |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent decoders | Enables two simultaneous 2-to-4 decode operations on one IC - reduces board space vs. discrete 74LS139 use. |
| Active-low outputs and enables | Direct interface with common cathode displays, NPN transistor drivers, or open-collector bus systems without inverters. |
| TTL-compatible input thresholds | VIL ≤ 0.8 V / VIH ≥ 2.0 V - ensures robust noise immunity and interoperability with 74xx, 74LSxx, and 74Fxx families. |
| Guaranteed fan-out of 20 LS-TTL loads | Supports driving multiple downstream logic inputs without external buffers in moderate-density control logic. |
| Standard SOP-16 footprint | Drop-in replacement for PDIP-16 in space-constrained designs using reflow-compatible surface-mount assembly. |
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. IC Role / Device Role / Timing Role: SN74LS156NSR acts as a dual address decoder - one section decodes A15–A14 for memory bank selection, the other decodes A13–A12 for chip-enable within bank. Use Value: Reduces component count versus two separate 74LS139s while preserving timing-critical decode path integrity with sub-25 ns delay. | Use Scenario: Enabling UART, timer, or ADC peripherals in an embedded controller via dedicated I/O address lines. IC Role / Device Role / Timing Role: SN74LS156NSR provides active-low peripheral select signals (/CS_UART, /CS_TIMER, etc.) synchronized to address strobes. Use Value: Eliminates need for discrete inverters or NAND gates to generate negative-enable logic required by many legacy peripherals. |
| LED Segment Driver Control | Industrial I/O Multiplexing |
Use Scenario: Driving four 7-segment LED displays using time-multiplexed scanning with common-cathode configuration. IC Role / Device Role / Timing Role: SN74LS156NSR selects which display is active per scan cycle via /Y₀–/Y₃ outputs tied to segment common cathodes. Use Value: Leverages native active-low outputs to directly sink current from LED segments without external transistor arrays. | Use Scenario: Routing sensor input signals (e.g., temperature, pressure) to a shared ADC channel in programmable logic controllers. IC Role / Device Role / Timing Role: SN74LS156NSR functions as a dual 1-of-4 analog multiplexer control unit - address lines select channel, /E enables sampling window. Use Value: Provides deterministic, glitch-free channel selection timing aligned to system clock edges due to consistent TTL propagation characteristics. |
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 |
|---|---|---|---|
| SN74LS139DR | Single dual 2-to-4 decoder with shared enable; identical logic but different pinout and enable structure (one /G vs. two /E). | Requires redesign of enable control wiring; lacks independent enable per section like SN74LS156NSR. | Choose when board layout allows pinout change and unified enable suffices for system timing. |
| SN74LS155ANSR | Complementary dual decoder with active-high outputs; otherwise identical pinout, timing, and package. | Requires inversion of downstream logic or level-shifting where active-low assertion is mandatory. | Choose when interfacing with circuits expecting high-active enables or outputs (e.g., certain PLD inputs). |
Compared with SN74LS139DR and SN74LS155ANSR, the SN74LS156NSR uniquely offers per-section active-low enables and active-low outputs in a fixed SOP-16 footprint - critical for systems requiring independent decoder gating or direct common-cathode load driving without added components.
Availability
SN74LS156NSR is available at Aetrix Electronics and suitable for industrial control panels, legacy test equipment, and repair of vintage computing hardware requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74LS156NSR 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 with broad industrial and automotive reach.
The SN74LS156NSR belongs to TI's legacy 74LS logic product line, designed specifically for reliable, low-power TTL-level digital interfacing in cost-sensitive, non-high-speed control applications.
FAQ
What is the primary function of the SN74LS156NSR?
The SN74LS156NSR is a dual 2-line-to-4-line decoder/demultiplexer that independently decodes two 2-bit binary inputs into four active-low outputs per section. Each section has its own address inputs (A₀, A₁) and active-low enable (/E), allowing parallel, isolated decoding operations essential for memory mapping and peripheral selection in 5-V TTL systems. Its design ensures deterministic timing and direct compatibility with legacy logic families.
Does the SN74LS156NSR support 3.3-V operation?
No, the SN74LS156NSR is specified only for 4.75 V to 5.25 V operation and is not rated for 3.3-V supply. Its input thresholds (VIL ≤ 0.8 V, VIH ≥ 2.0 V) and output drive levels are optimized for 5-V TTL systems. Using it with 3.3-V logic may result in marginal noise margins, undefined switching behavior, or failure to meet timing specs. For 3.3-V applications, consider modern alternatives like the SN74LV139A.
Can the SN74LS156NSR replace the SN74LS139 in an existing design?
The SN74LS156NSR is functionally similar to the SN74LS139 but differs in enable architecture: SN74LS156NSR has two independent active-low enables (/E₁ and /E₂), while SN74LS139 uses a single shared /G input. Pinout is incompatible - direct replacement requires PCB modification. However, logic behavior per section matches, so redesign is straightforward if independent enable control is needed or acceptable.
What is the maximum operating frequency for reliable decoding with the SN74LS156NSR?
The SN74LS156NSR does not specify a maximum clock frequency, as it is a combinational logic device. Its usable data rate is governed by propagation delay: tPD = 15 ns typical (25 ns max) from address/enable change to output transition. For stable decoding, input signals must be stable for ≥25 ns before and after enable assertion - supporting reliable operation up to ~10–15 MHz in well-designed synchronous systems with adequate setup/hold margins.
Is the SN74LS156NSR RoHS compliant?
Yes, the SN74LS156NSR is RoHS compliant, with lead finish of NiPdAu (NIPDAU) and MSL Level-1 rating for unlimited floor life at ≤30°C/60% RH. It meets JEDEC J-STD-020 moisture sensitivity requirements and is qualified for standard reflow soldering processes. The "Yes" RoHS status is confirmed in TI's official packaging addendum for this orderable part number.
SN74LS156NSR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 16-SOIC (0.209", 5.30mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Type:
- Decoder/Demultiplexer
- Circuit:
- 2 x 1:4
- Independent Circuits:
- 1
- Current - Output High, Low:
- 100µA, 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-SO
SN74LS156NSR FAQ
1.How can I place an order for SN74LS156NSR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS156NSR 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 SN74LS156NSR reliable?
The price and inventory of SN74LS156NSR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS156NSR is usually 5 days.
3.What payment methods are accepted for SN74LS156NSR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS156NSR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS156NSR?
SN74LS156NSR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS156NSR 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 SN74LS156NSR?
For technical support, including SN74LS156NSR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS156NSR requirements.
6.How does Aetrix verify that SN74LS156NSR is sourced from the original manufacturer or authorized distributors?
All SN74LS156NSR 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 SN74LS156NSR meets industry standards.
7.What is the process for return or replacement of SN74LS156NSR?
All SN74LS156NSR units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS156NSR, 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 SN74LS156NSR part is unused and in its original packaging.
Return procedure for SN74LS156NSR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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