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Texas Instruments SN74LS156NG4
- Part No.:
- SN74LS156NG4
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74LS156NG4.pdf
- Description:
- IC DECODER/DEMUX 2X1:4 16DIP
- Quantity:
- Payment:
- Shipping:
Inventory:2,748
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Product details
Overview
SN74LS156NG4 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 at VCC = 5 V and IOL = 8 mA, used for address decoding and data routing in TTL-based digital systems.
For engineers reviewing the SN74LS156NG4 datasheet, SN74LS156NG4 pinout, SN74LS156NG4 application, or SN74LS156NG4 equivalent, key selection considerations include its dual independent enable-controlled decoding paths, TTL-compatible input thresholds, guaranteed fan-out of 10 LS-TTL loads, and compatibility with legacy 74LS logic families in industrial control and instrumentation designs.
Technical Context
The SN74LS156NG4 integrates two identical 2-to-4 line decoders, each with active-low enable (G̅) and complementary outputs (Y₀–Y₃ and Y̅₀–Y̅₃), supporting both decoding and demultiplexing functions. Each decoder accepts two binary inputs (A, B) and generates four mutually exclusive active-low outputs.
It uses bipolar Schottky TTL technology, ensuring noise immunity with VIH ≥ 2.0 V and VIL ≤ 0.8 V, and drives standard LS-TTL loads with IOH = –0.4 mA and IOL = 8 mA. No internal latching or clocking is present - operation is purely combinational.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | 74LS TTL - ensures interoperability with legacy LS-series components and predictable DC/AC behavior in mixed-logic systems. |
| Propagation Delay | 22 ns max (tPLH/tPHL) - defines maximum timing budget for address decode paths in microprocessor peripheral interfaces. |
| Supply Voltage | 4.75 V to 5.25 V - requires tightly regulated +5 V rail; not tolerant of wider VCC excursions common in modern mixed-voltage designs. |
| Output Drive | 8 mA sink / –0.4 mA source - supports direct driving of up to 10 LS-TTL inputs without buffering in legacy backplane applications. |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade environments only; excludes extended industrial or automotive temperature ranges. |
| Input Thresholds | VIL ≤ 0.8 V, VIH ≥ 2.0 V - provides robust noise margin against ground bounce and crosstalk in densely routed PCBs. |
Pinout & Package
SN74LS156NG4 is housed in a 16-pin plastic dual in-line package (PDIP-N), 0.3-inch body width, with standard through-hole mounting and RoHS-compliant NiPdAu lead finish.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 15 | Enable (G̅) | Active-low chip select per decoder; both must be low for corresponding decoder outputs to respond to A/B inputs. |
| 2, 3, 5, 6 | Decoder 1 Inputs (A₁, B₁, G̅₁, G̅₁) | Dual enable inputs (pins 1 & 15) and binary address inputs (pins 2 & 3) configure first decoder's output activation. |
| 4, 7, 9, 12 | Decoder 1 Outputs (Y̅₀, Y̅₁, Y̅₂, Y̅₃) | Active-low decoded outputs; only one asserted per valid A₁B₁ combination when G̅₁ = LOW. |
| 10, 11, 13, 14 | Decoder 2 Inputs (A₂, B₂, G̅₂, G̅₂) | Second independent decoder set; pins 10 & 11 are A₂/B₂; pins 13 & 14 are redundant G̅₂ ties (per datasheet). |
| 8, 16 | GND / VCC | Pin 8 = Ground reference; Pin 16 = +5 V supply - critical for stable TTL switching and noise rejection. |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent decoders | Enables simultaneous address decoding for two memory banks or peripheral groups without external gating logic. |
| Complementary outputs (Y and Y̅) | Provides both true and inverted decoded signals per channel - eliminates need for external inverters in bus-enable or strobe-generation circuits. |
| Standard TTL input compatibility | Accepts direct connection to 74-series, 74LS-series, and microcontroller GPIOs without level-shifting or pull-up resistors. |
| No internal latches or clocks | Ensures deterministic, glitch-free combinational response - suitable for synchronous control signal generation where timing predictability is essential. |
Applications
| Memory Address Decoding | Peripheral Select Logic |
|---|---|
Use Scenario: Selecting one of four RAM/ROM chips in an 8-bit microprocessor system using A₀–A₁ address lines and a chip-enable signal. IC Role / Device Role / Timing Role: SN74LS156NG4 acts as a dual address decoder, converting 2-bit address segments into four discrete active-low chip-select lines with sub-25 ns latency. Use Value: Reduces external logic count by integrating two decoders in one package, minimizing board space and propagation delay versus discrete gate implementations. | Use Scenario: Routing control signals from a microcontroller to four distinct I/O expanders or sensor interfaces on a shared data bus. IC Role / Device Role / Timing Role: SN74LS156NG4 serves as a demultiplexer, directing a single command stream to one of four downstream devices based on 2-bit opcode bits. Use Value: Enables time-multiplexed peripheral access without bus contention, leveraging guaranteed fan-out and TTL-level compatibility for reliable signal integrity. |
| Industrial Control Panel | Legacy Test Equipment |
Use Scenario: Activating one of four relay drivers or LED indicators in a programmable logic controller (PLC) output module. IC Role / Device Role / Timing Role: SN74LS156NG4 functions as a static decoder, translating processor output port bits into discrete actuator enable signals with no timing constraints. Use Value: Provides galvanically isolated, noise-immune output control via direct TTL drive - eliminating need for additional buffer stages in low-speed industrial environments. | Use Scenario: Generating synchronized strobes and reset pulses in vintage automated test equipment (ATE) with fixed 5 V logic rails. IC Role / Device Role / Timing Role: SN74LS156NG4 delivers precise, repeatable timing edges for test pattern sequencing, relying on its consistent 22 ns propagation delay across temperature. Use Value: Ensures deterministic signal alignment between stimulus and measurement subsystems - critical for pass/fail validation in production test fixtures. |
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 | Same logic function and pinout; differs in internal enable structure (single active-low enable vs. dual enables on SN74LS156NG4) and slightly faster tpd (20 ns). | Requires external inversion for dual-enable operation; better suited for single-decoder-per-chip architectures. | Select SN74LS139N when consolidating enable logic externally or prioritizing minimal propagation delay over independent enable control. |
| SN74HC139N | CMOS family; operates from 2 V to 6 V; higher noise immunity (VNM ≈ 1.5 V); slower tpd (24 ns @ 4.5 V) but lower power (ICC < 8 µA). | Not TTL-compatible - requires level translation when interfacing with legacy 74LS systems; unsuitable for direct replacement without circuit review. | Choose SN74HC139N only in new designs with pure CMOS signaling or mixed-voltage domains where power efficiency outweighs compatibility. |
Compared with SN74LS156NG4, SN74LS139N offers identical pin compatibility and tighter timing but lacks independent dual enables, while SN74HC139N introduces voltage flexibility and ultra-low static power at the cost of TTL interoperability and increased design validation effort.
Availability
SN74LS156NG4 is available at Aetrix Electronics and suitable for legacy system repair, industrial control retrofitting, and educational lab setups requiring stable component supply and long-term obsolescence management.
Supply support for SN74LS156NG4 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 ICs, embedded processors, and logic devices with broad industrial and aerospace heritage.
The SN74LS156NG4 belongs to TI's legacy 74LS logic family, designed specifically for reliable, low-cost digital signal routing and address decoding in commercial-grade TTL systems deployed from the 1970s onward.
FAQ
What is the function of SN74LS156NG4 in a digital system?
The SN74LS156NG4 implements two independent 2-line-to-4-line decoders, each generating four active-low outputs from two binary inputs and an enable signal. It is used for address decoding, peripheral selection, and signal demultiplexing in TTL-based systems. Its dual-decoder architecture allows parallel decoding tasks without external logic, and it operates strictly as a combinational device with no internal storage or clocking.
Does SN74LS156NG4 support 3.3 V logic levels?
No, SN74LS156NG4 is a 5 V-only TTL device requiring VCC between 4.75 V and 5.25 V. Its input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V) and output drive characteristics are specified only for 5 V operation. Interfacing with 3.3 V systems requires level-shifting circuitry; direct connection risks unreliable switching or excessive input current.
What is the maximum fan-out capability of SN74LS156NG4?
SN74LS156NG4 guarantees a fan-out of 10 LS-TTL loads per output, based on its IOL = 8 mA and IOH = –0.4 mA specifications. This means each active-low output can reliably drive up to 10 standard 74LS inputs. Exceeding this limit may cause marginal logic thresholds or increased propagation delay due to capacitive loading and current sharing.
Is SN74LS156NG4 pin-compatible with SN74LS139N?
No, SN74LS156NG4 and SN74LS139N are not pin-compatible. While both are dual 2-to-4 decoders, SN74LS156NG4 uses separate enable inputs per decoder (pins 1 and 15), whereas SN74LS139N shares a single active-low enable (pin 1) for both decoders. Their pin mappings for inputs and outputs also differ, requiring PCB layout changes for substitution.
What does the 'G4' suffix indicate in SN74LS156NG4?
The 'G4' suffix in SN74LS156NG4 denotes Texas Instruments' Green packaging standard: RoHS-compliant, lead-free (NiPdAu finish), and halogen-free. It replaces earlier 'E4' or non-suffix variants and confirms compliance with environmental regulations without altering electrical or timing specifications - SN74LS156NG4 performs identically to SN74LS156N under the same operating conditions.
SN74LS156NG4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 16-DIP (0.300", 7.62mm)
- Packaging:
- Tube
- Product Status:
- Discontinued at Digi-Key
- 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:
- Through Hole
- Supplier Device Package:
- 16-PDIP
SN74LS156NG4 FAQ
1.How can I place an order for SN74LS156NG4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS156NG4 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 SN74LS156NG4 reliable?
The price and inventory of SN74LS156NG4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS156NG4 is usually 5 days.
3.What payment methods are accepted for SN74LS156NG4?
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Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS156NG4?
SN74LS156NG4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS156NG4 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 SN74LS156NG4?
For technical support, including SN74LS156NG4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS156NG4 requirements.
6.How does Aetrix verify that SN74LS156NG4 is sourced from the original manufacturer or authorized distributors?
All SN74LS156NG4 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 SN74LS156NG4 meets industry standards.
7.What is the process for return or replacement of SN74LS156NG4?
All SN74LS156NG4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS156NG4, 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 SN74LS156NG4 part is unused and in its original packaging.
Return procedure for SN74LS156NG4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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