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Texas Instruments SN74ALS138ANSR
- Part No.:
- SN74ALS138ANSR
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SOIC (0.209", 5.30mm Width)
- Datasheet:
-
SN74ALS138ANSR.pdf
- Description:
- IC DECODER/DEMUX 1 X 3:8 16SO
- Quantity:
- Payment:
- Shipping:
Inventory:1,227
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Product details
Overview
SN74ALS138ANSR from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in a 16-pin SOP (NS) package, designed for high-speed memory decoding and data routing. It features three enable inputs (G1, G2A, G2B), active-low outputs, propagation delays as low as 5 ns (tPLH) and 6 ns (tPHL) at VCC = 4.5–5.5 V, and operates over 0°C to 70°C.
For engineers reviewing the SN74ALS138ANSR datasheet, SN74ALS138ANSR pinout, SN74ALS138ANSR application, or SN74ALS138ANSR equivalent, this device is selected for systems requiring fast, low-power TTL-compatible decoding with cascading flexibility via dual active-low and single active-high enables.
Technical Context
The SN74ALS138ANSR implements positive-logic binary decoding with Schottky-clamped ALS (Advanced Low-Power Schottky) technology, enabling high-speed operation while maintaining TTL-compatible input thresholds (VIH = 2 V, VIL = 0.8 V). Its three enable inputs allow direct hierarchical expansion-e.g., a 24-line decoder without external inverters.
It uses totem-pole output drivers with guaranteed IOL = 4 mA (min) and IOH = –0.4 mA (min), supporting direct interfacing with standard TTL loads. No 3-state or open-collector functionality is present; all eight Y0–Y7 outputs are active-low, fully buffered, and mutually exclusive under valid enable conditions.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | ALS (Advanced Low-Power Schottky) - balances speed and power vs. standard TTL; typical ICC = 5–10 mA at VCC = 5.5 V. |
| Propagation Delay | tPLH/tPHL ≤ 22 ns (max) at VCC = 4.5–5.5 V, CL = 50 pF - ensures sub-25 ns system decode latency in memory address paths. |
| Supply Voltage | VCC = 4.5 V to 5.5 V - compatible with standard 5 V TTL rails; absolute max = 7 V. |
| Output Drive | IOL = 4 mA (min), IOH = –0.4 mA (min) - sufficient to drive ≥10 standard TTL inputs directly. |
| Operating Temp | 0°C to 70°C - commercial-grade rating; suitable for industrial control panels and embedded computing chassis. |
| Input Thresholds | VIH = 2.0 V (min), VIL = 0.8 V (max) - matches legacy TTL logic levels for seamless integration. |
Pinout & Package
SOP (Small Outline Package) NS, 16-pin, 1.27 mm pitch, 10.0 × 4.4 mm body, 2.00 mm max height per TI NS0016A outline. RoHS-compliant, NIPDAU lead finish, MSL Level-1.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (G2A) | Active-low enable | Must be LOW to activate decoding; used with G2B and G1 for 3-input cascade control. |
| 2 (G2B) | Active-low enable | Second active-low enable; both G2A and G2B must be LOW for function enable. |
| 3 (G1) | Active-high enable | Must be HIGH; simplifies multi-chip expansion by reducing external gate count. |
| 4 (C) | Binary select MSB | Most significant address bit (A2); determines Y4–Y7 vs. Y0–Y3 group selection. |
| 5 (B) | Binary select | Middle address bit (A1); combines with A and C for full 3-bit decode. |
| 6 (A) | Binary select LSB | Least significant address bit (A0); final bit resolving one-of-eight output activation. |
| 7 (Y0) | Active-low decoded output | Asserted LOW when A=B=C=0 and all enables active; drives memory chip-select or peripheral enable lines. |
| 8 (Y1) | Active-low decoded output | Asserted LOW for A=1, B=C=0; one of eight mutually exclusive outputs. |
| 9 (Y2) | Active-low decoded output | Asserted LOW for B=1, A=C=0; supports discrete peripheral addressing. |
| 10 (Y3) | Active-low decoded output | Asserted LOW for A=B=1, C=0; used in banked memory or I/O port decoding. |
| 11 (Y4) | Active-low decoded output | Asserted LOW for C=1, A=B=0; enables upper half of 8-output space. |
| 12 (Y5) | Active-low decoded output | Asserted LOW for C=1, A=1, B=0; supports modular address decoding trees. |
| 13 (Y6) | Active-low decoded output | Asserted LOW for C=1, B=1, A=0; used in multi-slot backplane systems. |
| 14 (Y7) | Active-low decoded output | Asserted LOW only when A=B=C=1; final output in 3-to-8 decode map. |
| 15 (VCC) | Power supply | +5 V supply pin; decoupling capacitor required near pin for noise immunity. |
| 16 (GND) | Ground reference | Signal and power return; must be low-impedance path to minimize ground bounce. |
Key Features
| Feature | Design Value |
|---|---|
| Three enable inputs | Enables hierarchical decoding: two active-low (G2A/G2B) + one active-high (G1) reduce need for external inverters in multi-device systems. |
| ALS Schottky technology | Delivers 5–22 ns propagation delay with 5–10 mA supply current - optimal for high-speed 5 V TTL systems where LS is too slow and AS draws excess power. |
| Standardized pinout | Pin-compatible across SN74ALS138A variants (D, N, NS packages) - allows drop-in replacement during board redesign or sourcing shifts. |
| Commercial temperature range | 0°C to 70°C operation with guaranteed parameters - validated for use in office equipment, test instrumentation, and industrial HMIs. |
| TTL-compatible interface | VIH = 2.0 V / VIL = 0.8 V thresholds and totem-pole outputs ensure interoperability with legacy 74xx, 74LSxx, and microcontroller GPIOs. |
Applications
| Memory Address Decoding | Data Routing in Bus Systems |
|---|---|
Use Scenario: Selecting one of eight SRAM or ROM chips in a 64 KB memory map using A15–A13 as C–A inputs. IC Role / Device Role / Timing Role: SN74ALS138ANSR acts as primary address decoder, asserting individual /CS lines with <22 ns delay to meet memory access timing budgets. Use Value: Eliminates need for discrete NAND gates or PLD logic, reducing BOM count and PCB area while guaranteeing deterministic decode timing. | Use Scenario: Directing serial data from a UART or SPI controller to one of eight peripheral UARTs or sensor interfaces. IC Role / Device Role / Timing Role: SN74ALS138ANSR functions as a demultiplexer, using G1 as data input and A/B/C as channel select lines to route signals. Use Value: Enables single-controller multi-peripheral communication without software polling or additional bus arbitration hardware. |
| Industrial I/O Expansion | Legacy System Logic Replacement |
Use Scenario: Expanding digital I/O on a PLC CPU module by decoding address lines to enable eight isolated relay driver ICs. IC Role / Device Role / Timing Role: SN74ALS138ANSR provides parallel enable control to relay drivers, synchronized with CPU write strobes. Use Value: Supports real-time deterministic I/O activation with no firmware overhead, critical for motion control safety interlocks. | Use Scenario: Replacing obsolete 74LS138 in a field-deployed medical analyzer's mainboard to restore supply continuity. IC Role / Device Role / Timing Role: SN74ALS138ANSR serves as pin- and function-compatible upgrade, delivering faster propagation and lower ICC than LS. Use Value: Extends product lifecycle without PCB rework; meets same timing margins while reducing power dissipation by ~30%. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar decoder/demultiplexer applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74AS138NSR | Faster tPLH/tPHL (≤10 ns max), higher IOL (20 mA), but higher ICC (14–20 mA) and identical pinout/package. | Better suited for ultra-high-speed bus arbitration or driving heavier capacitive loads; less ideal for power-constrained designs. | Select SN74AS138NSR when propagation delay <10 ns is mandatory and supply current budget allows ≥14 mA. |
| SN74HC138DR | CMOS family, wider VCC range (2–6 V), lower ICC (<8 µA), but slower (tPD ≤ 24 ns @ 4.5 V) and non-TTL input thresholds. | Requires level-shifting for legacy 5 V TTL systems; preferred in mixed-voltage or battery-powered applications. | Choose SN74HC138DR for new low-power designs with 3.3 V logic or flexible supply rails; not drop-in for TTL-only systems. |
Compared with SN74AS138NSR, SN74ALS138ANSR trades 10 ns speed for 50% lower supply current; versus SN74HC138DR, it guarantees TTL compatibility and deterministic timing in legacy 5 V environments but consumes more static power.
Availability
SN74ALS138ANSR is available at Aetrix Electronics and suitable for memory decoding, industrial I/O expansion, bus data routing, and legacy system repair requiring stable component supply and long-term sourcing assurance.
Supply support for SN74ALS138ANSR 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 for industrial, automotive, and communications markets.
The SN74ALS138ANSR belongs to TI's legacy 74ALS logic family, engineered specifically for high-speed memory decoding and data transmission systems where propagation delay and TTL compatibility are critical design constraints.
FAQ
What is the maximum propagation delay of the SN74ALS138ANSR under recommended operating conditions?
The SN74ALS138ANSR has a maximum propagation delay of 22 ns for tPLH (input to rising output) and 18 ns for tPHL (input to falling output), measured at VCC = 4.5–5.5 V, CL = 50 pF, and TA = 0°C to 70°C. These values are specified in the official SDAS055E datasheet and reflect worst-case performance across voltage and temperature.
Does the SN74ALS138ANSR support 3-state outputs?
No, the SN74ALS138ANSR does not feature 3-state outputs. It uses standard totem-pole (push-pull) active-low outputs (Y0–Y7). All outputs are always driven - either HIGH (inactive) or LOW (active) - with no high-impedance state. For bus-sharing applications requiring tri-state capability, consider alternatives like SN74ALS138A variants with output enable controls (not applicable to SN74ALS138ANSR).
Can the SN74ALS138ANSR be used as a demultiplexer?
Yes, the SN74ALS138ANSR can function as a 1-to-8 demultiplexer. By holding the binary select inputs (A, B, C) constant and applying the data signal to an enable input - typically G1 (active-high) - the input is routed to the corresponding Yx output determined by A/B/C. This is explicitly supported in the functional description and timing diagrams of the SN74ALS138ANSR datasheet.
What is the package type and lead finish of the SN74ALS138ANSR?
The SN74ALS138ANSR uses a 16-pin SOP (Small Outline Package) with NS package drawing, 1.27 mm pitch, and 10.0 × 4.4 mm body dimensions. Its lead finish is NiPdAu (NIPDAU), RoHS-compliant, with Moisture Sensitivity Level (MSL) rating of Level-1 (unlimited floor life at ≤30°C/60% RH), per TI's official packaging documentation.
How does the SN74ALS138ANSR differ from the SN74LS138 in terms of performance?
The SN74ALS138ANSR offers significantly faster propagation delays (≤22 ns vs. ≤34 ns for SN74LS138), lower power consumption (ICC ≈ 5–10 mA vs. 19 mA), and improved noise immunity due to Schottky clamping. Both share identical pinout and TTL-compatible logic thresholds, making SN74ALS138ANSR a direct, performance-enhancing drop-in replacement for SN74LS138 in existing 5 V designs.
SN74ALS138ANSR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 16-SOIC (0.209", 5.30mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Type:
- Decoder/Demultiplexer
- Circuit:
- 1 x 3:8
- Independent Circuits:
- 1
- Current - Output High, Low:
- 400µA, 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-SO
SN74ALS138ANSR FAQ
1.How can I place an order for SN74ALS138ANSR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS138ANSR 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 SN74ALS138ANSR reliable?
The price and inventory of SN74ALS138ANSR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS138ANSR is usually 5 days.
3.What payment methods are accepted for SN74ALS138ANSR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS138ANSR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS138ANSR?
SN74ALS138ANSR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS138ANSR 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 SN74ALS138ANSR?
For technical support, including SN74ALS138ANSR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS138ANSR requirements.
6.How does Aetrix verify that SN74ALS138ANSR is sourced from the original manufacturer or authorized distributors?
All SN74ALS138ANSR 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 SN74ALS138ANSR meets industry standards.
7.What is the process for return or replacement of SN74ALS138ANSR?
All SN74ALS138ANSR units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS138ANSR, 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 SN74ALS138ANSR part is unused and in its original packaging.
Return procedure for SN74ALS138ANSR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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