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Texas Instruments SN74ALS156DRE4
- Part No.:
- SN74ALS156DRE4
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
SN74ALS156DRE4.pdf
- Description:
- IC DECODER/DEMUX 2X1:4 16SOIC
- Quantity:
- Payment:
- Shipping:
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Product details
Overview
SN74ALS156DRE4 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: input 1C is inverted at outputs (1Y0–1Y3), while 2C passes non-inverted to 2Y0–2Y3. It operates from 4.5 V to 5.5 V, supports 0°C to 70°C ambient, and delivers propagation delays as low as 6 ns (tPHL) with 8 mA sink capability. It enables 3-line-to-8-line decoding or 1-line-to-8-line demultiplexing when sections are cascaded via shared C and G inputs - used in legacy TTL-based address decoding and data routing subsystems.
For engineers reviewing the SN74ALS156DRE4 datasheet, SN74ALS156DRE4 pinout, SN74ALS156DRE4 application, or SN74ALS156DRE4 equivalent, key selection considerations include its dual-section enable control, differential inversion per section, Schottky-clamped inputs for ringing suppression, and SOIC-16 package compatibility with industrial board layouts requiring discrete logic density and legacy 5-V TTL interoperability.
Technical Context
The SN74ALS156DRE4 implements two independent 2:4 decoder/demux sections sharing address lines A and B but featuring separate data inputs (1C, 2C) and strobe enables (1G, 2G). Each section decodes binary inputs into four active-low outputs (e.g., 1Y0–1Y3), with 1C inverted and 2C non-inverted - enabling direct 3:8 functionality without external gates when 1C and 2C are tied together and strobes synchronized.
Its logic diagram confirms totem-pole (non-open-collector) outputs with Schottky-clamped inputs, supporting standard TTL fan-out and noise immunity. Timing is characterized across VCC = 4.5–5.5 V and CL = 50 pF, with tPLH/tPHL asymmetry reflecting ALS-family optimization for speed over power - e.g., 6 ns minimum tPHL versus 7 ns minimum tPLH on critical paths like 1G→1Y.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - ensures compatibility with standard 5-V TTL supply rails and tolerance against rail droop in dense logic systems. |
| Output Drive (IOL) | 8 mA - supports direct interface to multiple standard TTL inputs (fan-out ≥20) without buffering. |
| Propagation Delay (tPHL) | 6 ns min (A/B → Y) - enables high-speed address decoding in microprocessor bus cycles with ≤25 ns access windows. |
| Input Clamping | High-performance Schottky diodes - suppresses transmission-line ringing on long PCB traces, reducing need for external termination. |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade embedded control and instrumentation applications, not extended industrial or automotive. |
| Logic Family | Advanced Low-Power Schottky (ALS) - provides 2× speed improvement over standard LS TTL at comparable power. |
Pinout & Package
SN74ALS156DRE4 is housed in a 16-pin SOIC (D) package with 1.27 mm pitch, JEDEC MS-012AC compliant, and RoHS-compliant NiPdAu lead finish. The package supports surface-mount assembly with Level-1 moisture sensitivity rating (unlimited floor life at ≤30°C/60% RH).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1C | Data input (Section 1) | Inverted at outputs 1Y0–1Y3 - enables direct use as one half of a 3:8 decoder when combined with non-inverted 2C path. |
| 1G | Strobe enable (Section 1) | Active-low enable - allows independent gating of Section 1 outputs without affecting Section 2 timing or state. |
| A, B | Binary address inputs | Shared by both sections - reduces PCB trace count and simplifies address-bus routing in multi-channel decode systems. |
| 1Y0–1Y3 | Active-low decoded outputs (Section 1) | Outputs go low on match - directly drives enable lines of memory chips or peripheral select logic with TTL-compatible thresholds. |
| 2C | Data input (Section 2) | Non-inverted at outputs 2Y0–2Y3 - complements 1C to form full 3:8 demux when C inputs are tied and strobes synchronized. |
| 2G | Strobe enable (Section 2) | Independent active-low control - permits dynamic partitioning of decode space between two subsystems on same address bus. |
| VCC, GND | Power supply terminals | Single 5-V supply with dedicated ground - eliminates need for dual-rail support and simplifies power distribution in mixed-logic boards. |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent decode sections | Enables simultaneous 2:4 decoding of two separate data streams using shared A/B address lines - reduces component count in multi-peripheral interfaces. |
| Complementary data paths (inverted/non-inverted) | Eliminates need for external inverters when implementing full 3:8 decoding - saves board space and propagation delay in address expansion circuits. |
| Individual strobe enables (1G, 2G) | Supports selective activation of either section during bus arbitration or time-multiplexed peripheral access - improves system-level timing control. |
| Schottky-clamped inputs | Reduces switching noise and overshoot on unterminated backplanes or long traces - enhances signal integrity without added termination components. |
| ALS logic family performance | Delivers 6 ns minimum tPHL at 5 V - meets timing budgets for 20+ MHz CPU address strobes and legacy bus protocols like ISA or VME. |
Applications
| Memory Address Decoding | Peripheral Select Logic |
|---|---|
|
Use Scenario: Selecting one of eight RAM/ROM chips in a 16-bit microprocessor system using A0–A2 address lines and chip-enable strobes. IC Role / Device Role / Timing Role: Dual-section decoder maps A0/A1 to local 2:4 decode per bank, while shared C/G inputs extend to full 3:8 selection - acts as primary address-space partitioner. Use Value: Reduces gate count vs. discrete 74LS138 + inverter; enables bank-switching via independent 1G/2G control without address re-encoding. |
Use Scenario: Routing I/O read/write signals to up to eight UARTs, ADCs, or GPIO expanders on a shared data bus. IC Role / Device Role / Timing Role: Demultiplexer routes single data line to selected peripheral based on address bits and strobe - functions as bus-controlled channel selector. Use Value: Provides deterministic 6 ns max enable-to-output delay, ensuring setup/hold compliance for 10-MHz peripheral clock domains. |
| Legacy Bus Expansion | Industrial Control Logic |
|
Use Scenario: Adding parallel I/O capability to an ISA-bus PC/104 system using edge-triggered interrupt mapping and address-decoded I/O ports. IC Role / Device Role / Timing Role: Decoder generates chip-selects for custom I/O cards mapped to fixed port ranges - integrates with ISA address decode hierarchy. Use Value: Schottky-clamped inputs tolerate ISA bus ringing; SOIC-16 footprint fits compact PC/104 carrier boards with tight layout constraints. |
Use Scenario: Implementing safety-critical enable logic for motor drivers or solenoid banks in programmable logic controller (PLC) backplanes. IC Role / Device Role / Timing Role: Strobe-gated decoder validates command validity before asserting output enables - serves as hardware interlock stage. Use Value: Independent 1G/2G control allows redundant enable paths; 0°C–70°C rating matches industrial enclosure thermal profiles. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar dual decoder/demultiplexer applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS156N | Standard LS TTL family: slower (tPHL ≈ 15 ns), higher ICC (19 mA), no Schottky clamping. | Limited to lower-frequency systems (<8 MHz bus); less robust against trace ringing; requires external clamps in noisy environments. | Choose only if cost-sensitive and timing budget allows ≥2× delay margin; verify fan-out with LS loading rules. |
| SN74F156N | Fast TTL family: faster (tPHL ≈ 4 ns) but higher power (ICC ≈ 35 mA); no Schottky input clamping. | Better for high-speed timing-critical paths but increases thermal load and EMI; lacks ringing suppression for long traces. | Select when sub-10 ns propagation is mandatory and board layout includes controlled impedance or termination. |
Compared with SN74LS156N and SN74F156N, the SN74ALS156DRE4 delivers optimal balance of speed (6 ns tPHL), power efficiency (9 mA ICC), and signal integrity (Schottky clamping), making it the preferred choice for mid-speed industrial and legacy computing designs where reliability and layout simplicity are prioritized.
Availability
SN74ALS156DRE4 is available at Aetrix Electronics and suitable for memory address decoding, peripheral select logic, legacy bus expansion, and industrial control logic requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS156DRE4 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 global semiconductor leader founded in 1930, specializing in analog, embedded processing, and logic solutions with broad industrial, automotive, and communications reach.
The SN74ALS156DRE4 belongs to TI's legacy Advanced Low-Power Schottky (ALS) TTL logic family, designed specifically for high-reliability, medium-speed digital systems requiring improved speed-power trade-offs over standard LS TTL in commercial-temperature environments.
FAQ
What logic family does SN74ALS156DRE4 belong to, and how does it differ from standard 74LS devices?
The SN74ALS156DRE4 belongs to the Advanced Low-Power Schottky (ALS) TTL logic family. Compared to standard 74LS devices, it offers approximately twice the speed (e.g., 6 ns tPHL vs. ~15 ns for 74LS156) at roughly half the power consumption (9 mA ICC vs. 19 mA), while adding Schottky-clamped inputs for improved noise immunity. This makes SN74ALS156DRE4 suitable for denser, faster 5-V TTL systems where LS devices would bottleneck timing or overheat.
Can SN74ALS156DRE4 be used as a 3-line-to-8-line decoder, and what connections are required?
Yes, SN74ALS156DRE4 can function as a 3-line-to-8-line decoder. To do so, tie inputs 1C and 2C together as the third address bit (C), connect 1G and 2G together as the global strobe (G), and apply A and B to their respective pins. The inverting path (1C→1Y0–1Y3) and non-inverting path (2C→2Y0–2Y3) collectively generate all eight active-low outputs. No external gates are needed - this configuration is explicitly validated in the device's function tables.
What is the maximum output sink current supported by SN74ALS156DRE4, and how does it affect fan-out?
SN74ALS156DRE4 supports a guaranteed 8 mA low-level output current (IOL) per output pin under recommended operating conditions. At VCC = 4.5 V and TA = 25°C, this allows driving up to 20 standard TTL inputs (each requiring ~0.4 mA IL) while maintaining VOL ≤ 0.4 V. This fan-out capability ensures reliable interfacing with legacy TTL loads without buffer amplification - a key design advantage in mixed-logic systems.
Is SN74ALS156DRE4 pin-compatible with other 16-pin dual decoder packages such as SN74LS156 or SN74F156?
Yes, SN74ALS156DRE4 is pin-compatible with SN74LS156 and SN74F156 in the same SOIC-16 (D) or PDIP-16 (N) packages. All share identical pin assignments for 1C, 1G, A, B, 1Y0–1Y3, VCC, GND, 2C, 2G, and 2Y0–2Y3. This allows direct replacement in existing layouts - though electrical behavior (speed, power, clamping) differs, requiring validation of timing margins and noise immunity in the target application.
What is the operating temperature range of SN74ALS156DRE4, and is it suitable for industrial environments?
SN74ALS156DRE4 is characterized for operation from 0°C to 70°C - the commercial temperature grade. While widely deployed in industrial control panels, it is not rated for extended industrial (−40°C to 85°C) or automotive temperatures. For true industrial use, thermal derating and enclosure-level temperature management must ensure junction temperature remains within spec; alternatively, consider modern replacements with wider temp ranges if ambient exceeds 70°C.
SN74ALS156DRE4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 16-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tape & Reel (TR)
- 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:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SOIC
SN74ALS156DRE4 FAQ
1.How can I place an order for SN74ALS156DRE4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS156DRE4 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 SN74ALS156DRE4 reliable?
The price and inventory of SN74ALS156DRE4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS156DRE4 is usually 5 days.
3.What payment methods are accepted for SN74ALS156DRE4?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS156DRE4 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS156DRE4?
SN74ALS156DRE4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS156DRE4 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 SN74ALS156DRE4?
For technical support, including SN74ALS156DRE4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS156DRE4 requirements.
6.How does Aetrix verify that SN74ALS156DRE4 is sourced from the original manufacturer or authorized distributors?
All SN74ALS156DRE4 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 SN74ALS156DRE4 meets industry standards.
7.What is the process for return or replacement of SN74ALS156DRE4?
All SN74ALS156DRE4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS156DRE4, 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 SN74ALS156DRE4 part is unused and in its original packaging.
Return procedure for SN74ALS156DRE4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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