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Texas Instruments SN54ALS138AJ
- Part No.:
- SN54ALS138AJ
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-CDIP (0.300", 7.62mm)
- Datasheet:
-
SN54ALS138AJ.pdf
- Description:
- 3-LINE TO 8-LINE DECODERS/DEMULT
- Quantity:
- Payment:
- Shipping:
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Product details
Overview
SN54ALS138AJ from Texas Instruments is a military-grade 3-line to 8-line decoder/demultiplexer in a 16-pin ceramic dual in-line package (CDIP-J), featuring active-low G2A/G2B and active-high G1 enables, propagation delays as low as 2 ns (tPLH/tPHL), and operation across –55°C to 125°C for high-speed memory decoding and data routing in avionics and ruggedized control systems.
For engineers reviewing the SN54ALS138AJ datasheet, SN54ALS138AJ pinout, SN54ALS138AJ application, or SN54ALS138AJ equivalent, this device supports cascaded decoding without external inverters, delivers TTL-compatible output drive (IOL = 4 mA min), and integrates Schottky-clamped logic for minimized system decoding delay in time-critical embedded subsystems.
Technical Context
The SN54ALS138AJ implements positive-logic binary decoding with three independent enable inputs (G1, G2A, G2B) that collectively gate all eight Y0–Y7 outputs - only one output goes low per valid input combination. Its internal architecture uses NAND-based logic with Schottky diode clamping to achieve fast switching while maintaining TTL voltage thresholds.
It operates strictly as a combinational logic device with no internal latching or clocking; all outputs respond asynchronously to input changes. The enable structure allows direct implementation of 24-line decoding without external inverters and 32-line decoding with only one added inverter - critical for hierarchical address decoding in large memory maps.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - compatible with standard 5 V TTL supply rails and tolerant of transient droop during high-current switching. |
| Propagation Delay (tPHL/tPLH) | 2 ns (min) to 22 ns (max) at VCC = 4.5–5.5 V, CL = 50 pF - ensures sub-25 ns worst-case address decode latency in high-speed memory systems. |
| Output Drive (IOL) | 4 mA minimum at VOL ≤ 0.4 V - sufficient to directly drive multiple TTL inputs or small capacitive loads without buffering. |
| Input Thresholds (VIH/VIL) | VIH ≥ 2.0 V, VIL ≤ 0.7 V - fully compatible with standard TTL logic families and robust against noise margin degradation. |
| Operating Temperature | –55°C to +125°C - qualified for extended military and aerospace applications where thermal cycling and extreme ambient conditions are present. |
| Supply Current (ICC) | 5 mA typical, 10 mA max at VCC = 5.5 V - enables predictable power budgeting in multi-device decoding trees. |
Pinout & Package
Ceramic Dual In-Line Package (CDIP-J), 16-pin, 300-mil width, hermetically sealed, lead finish: SNPB (tin-lead), MSL rating: N/A (non-MSL applicable).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (G2A) | Active-low enable | Must be low to activate decoder; used with G2B and G1 to form 3-input enable AND function. |
| 2 (G2B) | Active-low enable | Second active-low enable; both G2A and G2B must be low for decode to proceed. |
| 3 (G1) | Active-high enable | Primary enable; high level required alongside low G2A/G2B to enable outputs. |
| 4 (C) | Binary select MSB | Most significant address bit (A2) determining output line selection (Y0–Y7). |
| 5 (B) | Binary select middle | Address bit A1; combined with A and C to generate 3-bit binary code for output mapping. |
| 6 (A) | Binary select LSB | Least significant address bit (A0); full 3-bit input selects exactly one of eight active-low outputs. |
| 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 when A=1, B=C=0; provides discrete channel selection in demultiplexing configurations. |
| 9 (Y2) | Active-low decoded output | Asserted low for A=0,B=1,C=0; used in segmented I/O address decoding for microcontroller peripherals. |
| 10 (Y3) | Active-low decoded output | Asserted low for A=B=1,C=0; supports bank-select logic in multi-bank memory architectures. |
| 11 (Y4) | Active-low decoded output | Asserted low for A=C=0,B=1; enables selective activation of interrupt vectors or DMA channels. |
| 12 (Y5) | Active-low decoded output | Asserted low for A=1,C=0,B=1; used in programmable logic interface expansion with fixed decode windows. |
| 13 (Y6) | Active-low decoded output | Asserted low for A=0,C=1,B=1; facilitates modular firmware partitioning via hardware address decode. |
| 14 (Y7) | Active-low decoded output | Asserted low only when A=B=C=1; final output in full 3-to-8 decode map, often reserved for system reset or watchdog enable. |
| 15 (NC) | No internal connection | Unbonded pin; must remain unconnected - no routing or grounding required. |
| 16 (VCC) | Positive supply | 5 V nominal power rail; decoupling capacitor (0.1 µF) recommended adjacent to pin for noise suppression. |
Key Features
| Feature | Design Value |
|---|---|
| Three enable inputs (G1, G2A, G2B) | Enables hierarchical decoding trees without external logic - reduces gate count and PCB area in multi-chip select systems. |
| Sub-25 ns max propagation delay | Minimizes cumulative timing skew in address decode paths, enabling reliable operation with >40 MHz bus clocks in legacy microprocessor designs. |
| TTL-compatible input/output levels | Direct interoperability with 74LS, 74F, and other bipolar TTL families without level-shifting circuitry. |
| Military temperature qualification (–55°C to 125°C) | Validated for deployment in airborne, spaceborne, and ground-mobile platforms subject to extreme thermal environments. |
| Hermetic CDIP-J packaging | Provides long-term reliability and moisture resistance in high-humidity or corrosive operational settings. |
Applications
| Aerospace Avionics Bus Decoding | Industrial Programmable Logic Controller (PLC) I/O Expansion |
|---|---|
Use Scenario: Decoding 16-bit address bus segments to select discrete memory banks and peripheral registers in flight control computers. IC Role / Device Role / Timing Role: Primary address decoder for non-volatile configuration memory and sensor interface ICs, operating synchronously with CPU address strobes. Use Value: Sub-22 ns tPHL ensures decode completion before next clock edge in 25 MHz Z8000-based systems, eliminating wait-state insertion. | Use Scenario: Expanding discrete digital I/O capacity across multiple backplane slots using shared address/data bus architecture. IC Role / Device Role / Timing Role: Cascaded enable-controlled decoder driving slot-specific enable signals for isolated I/O modules. Use Value: Three enable inputs allow daisy-chained decoding of up to 24 I/O slots without external inverters, reducing component count by 30% vs. discrete gate solutions. |
| Military Communications Equipment Address Mapping | Ruggedized Test & Measurement Instrumentation |
Use Scenario: Selecting between RF transceiver banks, encryption modules, and telemetry interfaces in secure tactical radios. IC Role / Device Role / Timing Role: Hardware-based address decoder implementing fixed-function memory-mapped peripheral selection under MIL-STD-1553B timing constraints. Use Value: –55°C to 125°C operation guarantees uninterrupted decode functionality during rapid thermal transients in desert or arctic deployments. | Use Scenario: Routing trigger and calibration signals to multiple analog front-end channels in portable spectrum analyzers. IC Role / Device Role / Timing Role: Demultiplexer converting serial control commands into parallel channel-enable pulses for synchronized ADC sampling. Use Value: Active-low outputs directly interface with enable pins of precision op-amps and analog switches, eliminating need for external inverters in signal path. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar 3-to-8 decoder applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN54AS138J | Faster propagation delay (2–11 ns vs. 2–22 ns), higher IOL (20 mA vs. 4 mA), but higher ICC (14–20 mA vs. 5–10 mA). | Better suited for ultra-high-speed bus arbitration where drive strength and speed outweigh power efficiency. | Select SN54AS138J when decoding paths require <12 ns worst-case delay and load capacitance exceeds 50 pF. |
| SN74ALS138AN | Commercial temperature range (0°C to 70°C), plastic DIP package, RoHS-compliant NiPdAu lead finish. | Intended for cost-sensitive industrial control boards not requiring extended temperature or hermetic reliability. | Choose SN74ALS138AN for non-military applications where procurement cost, reflow compatibility, and supply chain availability are prioritized. |
Compared with SN54AS138J, SN54ALS138AJ trades speed and drive strength for lower power and proven long-term reliability in harsh environments; compared with SN74ALS138AN, it maintains identical logic behavior but adds military-grade thermal and hermetic performance at higher unit cost and longer lead times.
Availability
SN54ALS138AJ is available at Aetrix Electronics and suitable for aerospace avionics, military communications equipment, and ruggedized test instrumentation requiring stable component supply across extended temperature ranges and long product lifecycles.
Supply support for SN54ALS138AJ 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 high-reliability logic products for industrial, automotive, and defense markets.
The SN54ALS138AJ belongs to TI's military-qualified ALS (Advanced Low-Power Schottky) logic family, designed specifically for high-speed memory decoding and data-routing applications in mission-critical systems where timing predictability and environmental resilience are mandatory.
FAQ
What is the maximum operating temperature range for the SN54ALS138AJ?
The SN54ALS138AJ is characterized for continuous operation from –55°C to +125°C, meeting MIL-PRF-38535 requirements for Class B military-grade devices. This range is validated through temperature cycling, burn-in, and parametric testing across extremes - ensuring reliable decode functionality in jet engine bays, satellite payloads, and desert-deployed radios. The SN54ALS138AJ maintains specified propagation delay and output drive within this full range.
Does the SN54ALS138AJ support cascading with other decoders without external logic?
Yes, the SN54ALS138AJ supports cascading via its three enable inputs (G1, G2A, G2B): two active-low (G2A, G2B) and one active-high (G1). This configuration allows direct implementation of a 24-line decoder using three SN54ALS138AJ units without any external inverters, and a 32-line decoder with only one added inverter - significantly simplifying hierarchical address decoding in large memory systems.
What package type and pin count does the SN54ALS138AJ use?
The SN54ALS138AJ uses a 16-pin ceramic dual in-line package (CDIP-J), 300-mil width, with hermetic sealing and tin-lead (SNPB) lead finish. Pinout matches industry-standard 74-series decoder layouts, enabling drop-in replacement in legacy military schematics. The package includes two NC (no-connect) pins - pin 15 and pin 9 - which must remain unconnected per datasheet guidance.
How does the SN54ALS138AJ differ from the commercial SN74ALS138A variant?
The SN54ALS138AJ differs from SN74ALS138A primarily in temperature rating (–55°C to 125°C vs. 0°C to 70°C), packaging (hermetic ceramic CDIP-J vs. plastic PDIP-N or SOIC-D), and qualification (MIL-PRF-38535 Class B vs. commercial grade). Electrical specs are otherwise identical - same VCC range, propagation delays, and drive capability - making SN54ALS138AJ the direct military-spec counterpart.
Can the SN54ALS138AJ be used as a demultiplexer?
Yes, the SN54ALS138AJ can function as a 1-to-8 demultiplexer by using one of its enable inputs (e.g., G1) as the data input while holding the other two enables (G2A, G2B) inactive, and applying address bits to A, B, C. When G1 is high and G2A/G2B are low, the selected Yx output mirrors the G1 logic state - allowing serial data distribution to eight parallel destinations with precise timing control.
SN54ALS138AJ Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 54ALS
- Package/Case:
- 16-CDIP (0.300", 7.62mm)
- Packaging:
- Tube
- Product Status:
- Active
- Type:
- Decoder/Demultiplexer
- Circuit:
- 1 x 3:8
- Independent Circuits:
- 1
- Current - Output High, Low:
- 400µA, 4mA
- Voltage Supply Source:
- Single Supply
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- -55°C ~ 125°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 16-CDIP
SN54ALS138AJ FAQ
1.How can I place an order for SN54ALS138AJ through Aetrix?
Please submit a Request for Quotation (RFQ) for SN54ALS138AJ 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 SN54ALS138AJ reliable?
The price and inventory of SN54ALS138AJ are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN54ALS138AJ is usually 5 days.
3.What payment methods are accepted for SN54ALS138AJ?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN54ALS138AJ transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN54ALS138AJ?
SN54ALS138AJ orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN54ALS138AJ 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 SN54ALS138AJ?
For technical support, including SN54ALS138AJ datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN54ALS138AJ requirements.
6.How does Aetrix verify that SN54ALS138AJ is sourced from the original manufacturer or authorized distributors?
All SN54ALS138AJ 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 SN54ALS138AJ meets industry standards.
7.What is the process for return or replacement of SN54ALS138AJ?
All SN54ALS138AJ units undergo pre-shipment inspection (PSI). If there is an issue with SN54ALS138AJ, 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 SN54ALS138AJ part is unused and in its original packaging.
Return procedure for SN54ALS138AJ:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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