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Texas Instruments SN74ALS139NS
- Part No.:
- SN74ALS139NS
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- -
- Datasheet:
-
SN74ALS139NS.pdf
- Description:
- DECODER/DEMUX DL 2-4 16SO
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Product details
Overview
SN74ALS139NS from Texas Instruments is a dual 2-line-to-4-line decoder/demultiplexer in SOP-16 package, designed for high-speed memory decoding and data routing. It features Schottky-clamped TTL logic, 3–14 ns propagation delay (tPLH/tPHL), 0°C to 70°C operating range, 4.5–5.5 V supply, and active-low enable inputs for cascading. Used in address decoding for SRAM and ROM systems where low system delay is critical.
For engineers reviewing the SN74ALS139NS datasheet, SN74ALS139NS pinout, SN74ALS139NS application, or SN74ALS139NS equivalent, this page delivers verified functional identity, validated SOP-16 terminal mapping, confirmed timing and drive specifications, and two rigorously cross-referenced alternative parts for memory interface design.
Technical Context
The SN74ALS139NS implements two independent 2-to-4 decoders with fully buffered, Schottky-clamped TTL inputs-each presenting only one normalized load. Its active-low enable (G) input serves dual roles: cascade control and data line in demultiplexing mode.
Propagation delays are specified under CL = 50 pF, RL = 500 Ω, and VCC = 4.5–5.5 V, with tPLH/tPHL ≤ 14 ns (max) at TA = 0°C to 70°C. Output drive capability is IOL = 8 mA (VOL ≤ 0.4 V) and IOH = –0.4 mA (VOH ≥ VCC – 2 V), ensuring compatibility with standard ALS/AS loads.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | ALS (Advanced Low-Power Schottky) TTL - enables high speed with reduced power vs. standard LS. |
| Propagation Delay | ≤14 ns max (A/B or G to Y) - ensures minimal added latency in memory address decode paths. |
| Supply Voltage | 4.5–5.5 V - compatible with standard 5 V TTL bus systems without regulation overhead. |
| Output Drive | IOL = 8 mA / VOH ≥ VCC – 2 V - supports fan-out of ≥20 to standard TTL inputs. |
| Operating Temp | 0°C to 70°C - qualified for commercial-grade embedded and industrial control applications. |
| Input Load | One normalized TTL load per input - simplifies driving circuit design and reduces loading on upstream gates. |
| Enable Logic | Active-low (G) per decoder - allows direct connection to memory chip-select or microcontroller GPIO with no inversion. |
Pinout & Package
SOP-16 (NS) package: 10.4 mm × 5.3 mm body, 1.27 mm pitch, 2.00 mm max height, gull-wing leads, RoHS-compliant NiPdAu finish, MSL Level-1.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | 1G (Decoder 1 Enable) | Active-low enable controlling outputs Y0–Y3 of first decoder; tied low for always-active operation. |
| 2 | 1A (Decoder 1 A Input) | LSB address bit input for first decoder; fully buffered, Schottky-clamped for noise immunity. |
| 3 | 1B (Decoder 1 B Input) | MSB address bit input for first decoder; identical electrical characteristics to 1A. |
| 4 | 1Y0 (Decoder 1 Output 0) | Active-low decoded output; asserted when 1G=L, 1A=L, 1B=L - used for chip select or strobe. |
| 5 | 1Y1 (Decoder 1 Output 1) | Active-low decoded output; asserted when 1G=L, 1A=H, 1B=L - drives second memory bank or peripheral. |
| 6 | 1Y2 (Decoder 1 Output 2) | Active-low decoded output; asserted when 1G=L, 1A=L, 1B=H - enables third device or function block. |
| 7 | 1Y3 (Decoder 1 Output 3) | Active-low decoded output; asserted when 1G=L, 1A=H, 1B=H - final selection line for 4-device decode group. |
| 8 | GND | Ground reference for all internal logic and output stages; requires low-impedance PCB plane connection. |
| 9 | 2Y0 (Decoder 2 Output 0) | Active-low decoded output of second decoder; independent timing and enable from first decoder. |
| 10 | 2Y1 (Decoder 2 Output 1) | Active-low output for second decoder's 01 state; supports parallel decode of separate address spaces. |
| 11 | 2Y2 (Decoder 2 Output 2) | Active-low output for second decoder's 10 state; enables modular expansion of decode tree. |
| 12 | 2Y3 (Decoder 2 Output 3) | Active-low output for second decoder's 11 state; provides full 2×4 decode coverage per package. |
| 13 | 2B (Decoder 2 B Input) | MSB address input for second decoder; electrically isolated from 1B but identical AC/DC specs. |
| 14 | 2A (Decoder 2 A Input) | LSB address input for second decoder; shares same input threshold (VIL = 0.8 V, VIH = 2 V) as 1A/1B. |
| 15 | 2G (Decoder 2 Enable) | Independent active-low enable for second decoder; allows selective activation of either decoder pair. |
| 16 | VCC | +5 V supply rail; bypass capacitor (0.1 µF ceramic) required within 10 mm of pin for stable switching. |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent decoders | Two 2-to-4 decoders share one SOP-16 package - reduces board space and interconnect count vs. discrete solutions. |
| Schottky-clamped inputs | High-performance diodes suppress line ringing and reduce input transient susceptibility - improves signal integrity in noisy environments. |
| Low propagation delay | Max 14 ns (G or A/B to Y) at 5 V - minimizes added latency in high-speed memory access paths, preserving effective system timing budget. |
| Buffered TTL-compatible inputs | Each input presents exactly one normalized TTL load - eliminates need for input buffering or fan-out management in cascaded designs. |
| Active-low enable per decoder | Separate 1G and 2G pins allow hierarchical decoding - e.g., 1G driven by upper address bits, 2G by lower bits for multi-level memory maps. |
Applications
| SRAM Address Decoding | ROM Selection Logic |
|---|---|
|
Use Scenario: Selecting one of four 8K×8 SRAM chips in a 32K-byte memory subsystem using A13–A14 address lines. IC Role / Device Role / Timing Role: SN74ALS139NS acts as primary address decoder; its 14 ns max delay ensures decoded chip-select signals arrive before memory access time expires. Use Value: Enables zero-wait-state operation with fast SRAMs (e.g., IDT71V256SA) by keeping decode delay well below typical 15 ns access times. |
Use Scenario: Enabling one of four EPROM devices in an 80C51-based controller, where upper address bits determine ROM bank. IC Role / Device Role / Timing Role: SN74ALS139NS provides active-low chip-enable signals synchronized to address valid windows via 2G/1G control. Use Value: Eliminates external inverters and reduces gate count by leveraging native active-low outputs directly tied to EPROM CE pins. |
| Peripheral I/O Multiplexing | Legacy Bus Expansion |
|
Use Scenario: Routing data from a single microcontroller port to four distinct peripherals (ADC, DAC, UART, GPIO expander) using address-select lines. IC Role / Device Role / Timing Role: SN74ALS139NS functions as a demultiplexer; G input driven by control register bit to gate data flow per peripheral. Use Value: Provides deterministic, glitch-free output enable timing (tPLZ/tPZH ≤ 15 ns) - prevents bus contention during peripheral switching. |
Use Scenario: Expanding ISA bus address decoding for add-in cards requiring dedicated I/O port ranges (e.g., 0x300–0x3FF). IC Role / Device Role / Timing Role: SN74ALS139NS generates sub-range selects (e.g., Y0–Y3 = 0x300–0x33F, 0x340–0x37F, etc.) from A8–A9 and IOR/IOW strobes. Use Value: Maintains strict ISA timing compliance with <15 ns propagation - avoids setup/hold violations on legacy bus controllers. |
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 | LS-family: slower (25 ns max delay), higher ICC (18 mA), same pinout and logic function. | Acceptable where speed <15 ns is not required; less suitable for >10 MHz address bus systems. | Choose SN74LS139N only if legacy LS compatibility or cost sensitivity outweighs speed requirements. |
| SN74HC139DR | CMOS family: wider VCC (2–6 V), lower ICC (<8 µA), but slower at 5 V (21 ns typ), different input thresholds. | Requires level-shifting if interfacing with TTL outputs; unsuitable for direct replacement in existing ALS designs. | Use SN74HC139DR only in new 3.3/5 V mixed-signal designs where ultra-low static power is prioritized over propagation speed. |
Compared with SN74ALS139NS, SN74LS139N trades speed for broader legacy compatibility, while SN74HC139DR sacrifices propagation performance for CMOS power efficiency and voltage flexibility - neither is pin- or timing-compatible without redesign.
Availability
SN74ALS139NS is available at Aetrix Electronics and suitable for SRAM decoding, ROM selection, peripheral demultiplexing, and legacy bus expansion requiring stable component supply across industrial and embedded production cycles.
Supply support for SN74ALS139NS 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, delivering analog, embedded processing, and logic solutions with emphasis on reliability, longevity, and industrial-grade qualification.
The SN74ALS139NS belongs to TI's legacy ALS logic product line, engineered specifically for high-speed memory decoding and data-routing systems where propagation delay and TTL compatibility are critical.
FAQ
What is the maximum propagation delay of the SN74ALS139NS under standard operating conditions?
The SN74ALS139NS has a maximum propagation delay of 14 ns (tPLH and tPHL) from any input (A, B, or G) to any output (Y0–Y3), measured at VCC = 4.5–5.5 V, CL = 50 pF, RL = 500 Ω, and TA = 0°C to 70°C. This value is confirmed in the SDAS204A datasheet Section 5, Switching Characteristics table.
Does the SN74ALS139NS support 3.3 V operation?
No, the SN74ALS139NS is an ALS-family TTL device rated for 4.5–5.5 V operation only. Its input thresholds (VIH = 2 V min, VIL = 0.8 V max) and output drive levels are optimized for 5 V systems. Operating below 4.5 V risks unreliable logic states and increased propagation delay - the SN74ALS139NS must be used with a regulated 5 V supply.
How many normalized TTL loads does each input of the SN74ALS139NS represent?
Each input of the SN74ALS139NS represents exactly one normalized TTL load, as stated in the device description and confirmed by input current specs (IIH = 20 µA max, IIL = –0.1 mA max). This allows direct fan-out to up to 20 standard TTL inputs without buffering - a key design advantage for cascaded logic systems.
Can the SN74ALS139NS be used as a demultiplexer, and how is that implemented?
Yes, the SN74ALS139NS can operate as a dual 1-to-4 demultiplexer. The active-low enable (G) input serves as the data input, while A and B act as select lines. When G is driven with data and A/B with address bits, the selected Y output mirrors the inverted G signal - enabling time-multiplexed signal routing in bus arbitration or test equipment applications.
What is the thermal operating range and package type of the SN74ALS139NS?
The SN74ALS139NS is characterized for operation from 0°C to 70°C and packaged in a 16-pin SOP (NS) format per TI's NS0016A outline: 10.4 mm × 5.3 mm body, 1.27 mm pitch, 2.00 mm max height, gull-wing leads, and NiPdAu lead finish. This package is RoHS-compliant and rated MSL Level-1.
SN74ALS139NS Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- *
- Package/Case:
- -
- Packaging:
- Bulk
- Product Status:
- Active
- Type:
- -
- Circuit:
- -
- Independent Circuits:
- -
- Current - Output High, Low:
- -
- Voltage Supply Source:
- -
- Voltage - Supply:
- -
- Operating Temperature:
- -
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- -
- Supplier Device Package:
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SN74ALS139NS FAQ
1.How can I place an order for SN74ALS139NS through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS139NS 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 SN74ALS139NS reliable?
The price and inventory of SN74ALS139NS are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS139NS is usually 5 days.
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SN74ALS139NS orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS139NS 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 SN74ALS139NS?
For technical support, including SN74ALS139NS datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS139NS requirements.
6.How does Aetrix verify that SN74ALS139NS is sourced from the original manufacturer or authorized distributors?
All SN74ALS139NS 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 SN74ALS139NS meets industry standards.
7.What is the process for return or replacement of SN74ALS139NS?
All SN74ALS139NS units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS139NS, 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 SN74ALS139NS part is unused and in its original packaging.
Return procedure for SN74ALS139NS:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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