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Texas Instruments SN74ALS156DE4
- Part No.:
- SN74ALS156DE4
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
SN74ALS156DE4.pdf
- Description:
- IC DECODER/DEMUX 2X1:4 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,751
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Product details
Overview
SN74ALS156 from Texas Instruments is a dual 2-line-to-4-line decoder/demultiplexer IC with independent strobes (1G, 2G), common binary-address inputs (A, B), and complementary data paths: 1C inverted, 2C non-inverted. It operates at 4.5–5.5 V, supports 0°C to 70°C ambient, delivers 8 mA sink current per output, and achieves propagation delays as low as 6 ns (tPHL). It enables 3-line-to-8-line decoding without external gating when 1C and 2C are tied together.
For engineers reviewing the SN74ALS156 datasheet, SN74ALS156 pinout, SN74ALS156 application, or SN74ALS156 equivalent, key selection criteria include its dual-section enable control, Schottky-clamped inputs for ringing suppression, TTL-compatible voltage thresholds (VIH = 2 V, VIL = 0.8 V), and SOIC-16 packaging with Level-1 moisture sensitivity.
Technical Context
The SN74ALS156 implements two independent 2:4 decoder/demux sections sharing address lines A and B but featuring separate data inputs (1C, 2C) and strobes (1G, 2G). Each section drives four active-low outputs (1Y0–1Y3, 2Y0–2Y3) with totem-pole outputs and no 3-state capability.
Its logic architecture supports cascading via individual strobes and permits 3:8 decoding by connecting 1C and 2C (with inversion on 1C side) and tying 1G and 2G - enabling full 8-output selection using three address bits (C, B, A) and one shared strobe.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - compatible with standard 5 V TTL systems; tolerates supply variation without functional loss. |
| Output Sink Current (IOL) | 8 mA per output - sufficient to drive multiple TTL inputs or small LEDs directly. |
| Propagation Delay (tPHL) | 6 ns min / 25 ns max - ensures fast address decoding in high-speed bus control or memory select applications. |
| Input Thresholds | VIH = 2 V, VIL = 0.8 V - matches standard TTL logic levels; eliminates need for level-shifting in mixed-logic systems. |
| Operating Temperature | 0°C to 70°C - rated for commercial-grade environments including office equipment and industrial control panels. |
| Input Clamping | High-performance Schottky diodes - suppresses transmission-line ringing on long PCB traces or backplanes. |
Pinout & Package
SN74ALS156 is packaged in a 16-pin SOIC (D package), 300-mil wide, with gull-wing leads and RoHS-compliant NiPdAu finish. Moisture sensitivity level is Level-1 (unlimited floor life at ≤30°C/60% RH).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1C | Data input (Section 1) | Inverted path: applied logic is complemented before routing to 1Y0–1Y3 outputs. |
| 1G | Strobe enable (Section 1) | Active-low: Section 1 outputs enabled only when 1G = L; allows independent section gating. |
| A, B | Binary address inputs | Shared by both sections; select output line (0–3) within each enabled section. |
| 1Y0–1Y3 | Outputs (Section 1) | Active-low decoded/demuxed outputs; driven low per address + strobe condition. |
| GND (Pin 8) | Ground reference | Return path for all internal logic and output currents; must be low-impedance. |
| VCC (Pin 16) | Supply voltage | Primary power rail; bypassing with 0.1 µF ceramic capacitor near pin is recommended. |
| 2C | Data input (Section 2) | Non-inverted path: applied logic passes unchanged to 2Y0–2Y3 outputs. |
| 2G | Strobe enable (Section 2) | Active-low: controls Section 2 independently; enables cascaded 3:8 operation when tied to 1G. |
| 2Y0–2Y3 | Outputs (Section 2) | Active-low outputs mirroring Section 1 behavior but with non-inverted data path. |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent decode/demux sections | Enables simultaneous control of two 4-bit subsystems (e.g., two memory banks or peripheral groups) with shared addressing. |
| Individual strobe inputs (1G, 2G) | Permits dynamic enabling/disabling of each section without affecting the other - critical for time-multiplexed resource allocation. |
| Inverted + non-inverted data paths | Eliminates need for external inverters when implementing 3:8 decoding: tie 1C/2C and use 1C's inversion to generate complementary outputs. |
| Schottky-clamped inputs | Reduces signal reflection and overshoot on unterminated lines - simplifies layout in backplane or ribbon-cable interfacing. |
| TTL-compatible voltage thresholds | Ensures interoperability with legacy 74LS/74S families and microcontroller GPIOs without level translation. |
Applications
| Memory Address Decoding | Peripheral Select Logic |
|---|---|
Use Scenario: Selecting among four RAM chips in a 16-bit system using A0–A1 address lines and chip-enable strobes. IC Role / Device Role / Timing Role: Dual-section decoder routes A0/A1 to enable one of four memory banks per section; 1G/2G isolate read/write timing windows. Use Value: Reduces gate count vs. discrete NAND-based decoding; enables independent enable timing for interleaved memory access. | Use Scenario: Assigning I/O addresses to UART, SPI, and GPIO expanders on an 8-bit microcontroller bus. IC Role / Device Role / Timing Role: Acts as demultiplexer: microcontroller data bus drives 1C/2C while A/B select peripheral; strobes synchronize with bus cycle. Use Value: Provides deterministic, glitch-free peripheral selection with sub-25 ns propagation - avoids bus contention during address setup. |
| 3:8 Line Expansion | Legacy System Bus Control |
Use Scenario: Expanding a 3-bit opcode bus to eight discrete control signals in a vintage CPU control unit. IC Role / Device Role / Timing Role: Configured as 3:8 decoder using C (tied 1C/2C), A, B and shared G (1G/2G); outputs drive microcode sequencer inputs. Use Value: Achieves full 3:8 decoding in one IC without external gates - preserves board space and reduces propagation skew across outputs. | Use Scenario: Managing address strobes and data gating in a 1980s-era industrial PLC backplane with TTL-level signaling. IC Role / Device Role / Timing Role: Serves as dual demux: one section handles memory-mapped I/O strobes; the other manages interrupt vector decoding. Use Value: Schottky-clamped inputs suppress ringing on long backplane traces; 0°C–70°C rating ensures reliability in uncooled enclosures. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar decoder/demultiplexer applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS139N | Dual 2:4 decoder with non-inverted data paths only; no 1C inversion; slower tPHL (15 ns typ) and lower IOL (8 mA same). | Lacks built-in inversion path - requires external inverter for 3:8 mode; less flexible in mixed-signal routing. | Select when only non-inverted demux is needed and LS-family compatibility is mandatory. |
| SN74ALS138N | Single 3:8 decoder with three enable inputs (G1, G2A, G2B); no dual-section or independent strobes; faster tPHL (5 ns min). | Fixed 3:8 topology - cannot emulate dual 2:4 operation or independent section control; higher pin count (16-pin DIP same, but functionally distinct). | Select when full 3:8 decoding is primary requirement and cascading flexibility is not needed. |
Compared with SN74LS139N and SN74ALS138N, the SN74ALS156 uniquely combines dual-section independence, on-die inversion, and Schottky input clamping - making it optimal for systems requiring reconfigurable decode/demux partitioning and noise-immune bus interfacing.
Availability
SN74ALS156 is available at Aetrix Electronics and suitable for memory address decoding, peripheral select logic, 3:8 line expansion, and legacy system bus control requiring stable component supply and long-term obsolescence support.
Supply support for SN74ALS156 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 for industrial, automotive, and communications markets.
The SN74ALS156 belongs to TI's ALS (Advanced Low-Power Schottky) logic family - designed for high-speed, low-power TTL-compatible digital control in commercial-grade systems where propagation delay and input noise immunity are critical.
FAQ
What logic family does the SN74ALS156 belong to, and how does it differ from standard TTL?
The SN74ALS156 belongs to Texas Instruments' Advanced Low-Power Schottky (ALS) logic family. It differs from standard TTL by integrating Schottky clamping diodes on all inputs to suppress ringing, offering faster propagation delays (as low as 6 ns tPHL), lower power consumption than 74S, and tighter voltage thresholds (VIH = 2 V, VIL = 0.8 V). The SN74ALS156 maintains full pin and functional compatibility with other 74ALS decoders while delivering improved noise immunity and speed over 74LS or 74F variants.
Can the SN74ALS156 be used as a 3-line-to-8-line decoder, and if so, how is it configured?
Yes, the SN74ALS156 can be configured as a 3-line-to-8-line decoder. Connect inputs 1C and 2C together to serve as the third address bit (C), tie 1G and 2G together as the single strobe (G), and apply A and B to the shared address inputs. Because 1C is inverted and 2C is non-inverted, the combined outputs 1Y0–1Y3 and 2Y0–2Y3 produce eight unique active-low selections corresponding to all combinations of C, A, and B - achieving full 3:8 decoding without external gates. This configuration is explicitly validated in the SN74ALS156 datasheet function tables.
What are the absolute maximum ratings for the SN74ALS156, and why are they important for PCB design?
The SN74ALS156 has an absolute maximum supply voltage (VCC) of 7 V and input voltage (VI) limit of 7 V; exceeding either risks permanent damage. Its operating temperature range is 0°C to 70°C, and storage range is −65°C to 150°C. These ratings are critical for PCB design because they define hard limits for transient protection - for example, series current-limiting resistors or clamping diodes may be needed on inputs exposed to hot-plug or ESD events. The 7 V VI rating also informs selection of upstream drivers: microcontroller GPIOs must not exceed this value, even during power sequencing mismatches. Observing these limits ensures long-term reliability in commercial applications.
Does the SN74ALS156 support 3-state outputs, and what output structure does it use instead?
No, the SN74ALS156 does not support 3-state outputs. It uses totem-pole (push-pull) output structures on all eight outputs (1Y0–1Y3, 2Y0–2Y3), meaning each output actively drives HIGH or LOW - never high-impedance. This design eliminates bus contention concerns in point-to-point decoding applications but prohibits direct connection to shared data buses. For applications requiring bus sharing, external open-collector buffers or a different device such as the SN74ALS158 (which offers 3-state) would be required. The SN74ALS156 datasheet confirms no 3-state functionality and provides load circuit diagrams exclusively for bi-state totem-pole operation.
What package options are available for the SN74ALS156, and which is recommended for new designs?
The SN74ALS156 is available in two package types: SOIC-16 (D package, e.g., SN74ALS156DR, SN74ALS156DRE4) and PDIP-16 (N package, e.g., SN74ALS156N). The SOIC version features RoHS-compliant NiPdAu lead finish, Level-1 MSL rating, and tape-and-reel packaging (2500 units/reel), making it ideal for automated SMT assembly. The PDIP variant remains available for prototyping and through-hole legacy systems. For new designs, the SOIC-16 (SN74ALS156DRE4) is recommended due to superior thermal performance, smaller footprint, and alignment with modern manufacturing standards - while maintaining full electrical and functional equivalence to the PDIP version.
SN74ALS156DE4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 16-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tube
- Product Status:
- Obsolete
- Type:
- Decoder/Demultiplexer
- Circuit:
- 2 x 1:4
- Independent Circuits:
- 1
- Current - Output High, Low:
- 100µA, 8mA
- Voltage Supply Source:
- Single Supply
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SOIC
SN74ALS156DE4 FAQ
1.How can I place an order for SN74ALS156DE4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS156DE4 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 SN74ALS156DE4 reliable?
The price and inventory of SN74ALS156DE4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS156DE4 is usually 5 days.
3.What payment methods are accepted for SN74ALS156DE4?
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SN74ALS156DE4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS156DE4 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 SN74ALS156DE4?
For technical support, including SN74ALS156DE4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS156DE4 requirements.
6.How does Aetrix verify that SN74ALS156DE4 is sourced from the original manufacturer or authorized distributors?
All SN74ALS156DE4 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 SN74ALS156DE4 meets industry standards.
7.What is the process for return or replacement of SN74ALS156DE4?
All SN74ALS156DE4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS156DE4, 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 SN74ALS156DE4 part is unused and in its original packaging.
Return procedure for SN74ALS156DE4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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