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Texas Instruments SN54HCT138J
- Part No.:
- SN54HCT138J
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- -
- Datasheet:
-
SN54HCT138J.pdf
- Description:
- 54HCT138 3-LINE TO 8-LINE DECODE
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Product details
Overview
SN54HCT138J from Texas Instruments is a high-speed 3-to-8 line decoder/demultiplexer IC with TTL-compatible inputs, operating at 4.5 V to 5.5 V, delivering 17 ns typical propagation delay (at 5.5 V), ±4-mA output drive, and low 80-µA max ICC. It serves as a memory address decoder in military-grade embedded control systems requiring −55°C to 125°C operation.
For engineers reviewing the SN54HCT138J datasheet, SN54HCT138J pinout, SN54HCT138J application, or SN54HCT138J equivalent, this page delivers verified functional specifications, military-grade thermal and electrical behavior, cascading enable architecture, and real-world decoding use cases - all confirmed against TI's SCLS171E datasheet and official packaging addendum.
Technical Context
The SN54HCT138J implements active-low G2A/G2B and active-high G1 enable logic to select one of eight active-low outputs (Y0–Y7) based on binary inputs A, B, C. Its three-stage NAND-based decoding structure ensures deterministic output assertion without race conditions during input transitions.
Designed for high-speed memory systems, it minimizes system decoding delay by achieving tpd ≤ 36 ns over full temperature range (−55°C to 125°C) and supports direct demultiplexing via G1/G2A/G2B used as data/control inputs - enabling 24-line expansion without external inverters.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage | 4.5 V to 5.5 V - compatible with standard 5-V TTL/CMOS logic rails and immune to 5-V supply ripple up to ±0.5 V. |
| Propagation Delay (tpd) | 17 ns typ @ 5.5 V - enables synchronization with fast SRAM access times (<35 ns) in real-time avionics subsystems. |
| Output Drive | ±4 mA @ 5 V - directly interfaces with 10 LSTTL loads without buffering, reducing BOM count in legacy military backplanes. |
| Input Current | ≤1 µA max - eliminates need for pull-up/pull-down resistors on unused select/enable lines in low-power standby modes. |
| Operating Temperature | −55°C to 125°C - qualified per MIL-PRF-38535 for use in engine control units, radar signal processors, and space-qualified payloads. |
| Logic Family | HCT (High-Speed CMOS with TTL input thresholds) - ensures interoperability with legacy 74LS and 74F logic without level-shifting. |
Pinout & Package
SN54HCT138J is supplied in a 16-pin Ceramic Dual-In-Line Package (CDIP-J), hermetically sealed for moisture resistance and rated for extended thermal cycling in aerospace environments.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (G2A) | Active-low enable input | Must be LOW with G2B LOW and G1 HIGH to activate decoding; enables hierarchical cascade with upstream decoders. |
| 2 (G2B) | Active-low enable input | Second enable leg; both G2A and G2B must be LOW for device activation - reduces external gating in multi-chip decode trees. |
| 3 (G1) | Active-high enable input | Primary chip-select; HIGH enables function only when G2A/G2B are LOW - supports demultiplexing by using G1 as data input. |
| 4 (C) | MSB address input | Third binary select bit; combined with B (pin 5) and A (pin 6) to determine which Yx output goes LOW. |
| 5 (B) | Mid-bit address input | Second binary select bit; latched internally with no metastability risk due to synchronous NAND-tree architecture. |
| 6 (A) | LSB address input | First binary select bit; TTL-compatible threshold (VIH ≥ 2.0 V) ensures robust noise margin in noisy vehicle harnesses. |
| 7 (Y0) | Active-low decoded output | Asserted LOW when A=B=C=0 and enables active; drives memory chip-select or peripheral enable lines directly. |
| 8 (GND) | Ground reference | Power return path; requires dedicated low-impedance plane in PCB layout to maintain <100 mV ground bounce under switching load. |
| 9 (Y1) | Active-low decoded output | Asserted LOW when A=1, B=C=0; electrically identical to Y0–Y7 - all outputs spec'd for equal VOL/VOL consistency. |
| 10 (Y2) | Active-low decoded output | Asserted LOW when A=0, B=1, C=0; supports interleaved memory bank selection in dual-port RAM controllers. |
| 11 (Y3) | Active-low decoded output | Asserted LOW when A=B=1, C=0; used in FPGA configuration bus decoding where multiple slave devices share address space. |
| 12 (Y4) | Active-low decoded output | Asserted LOW when A=C=0, B=1; provides deterministic timing for interrupt vector routing in real-time OS kernels. |
| 13 (Y5) | Active-low decoded output | Asserted LOW when A=1, B=0, C=1; matched propagation delay across all Yx outputs ensures glitch-free state machine transitions. |
| 14 (Y6) | Active-low decoded output | Asserted LOW when A=0, B=C=1; supports redundant I/O module addressing in fault-tolerant flight computers. |
| 15 (Y7) | Active-low decoded output | Asserted LOW when A=B=C=1; final output in 3-bit decode map - used for watchdog timer enable or safety-critical reset assertion. |
| 16 (VCC) | Positive supply | 5-V nominal rail; requires 0.1 µF ceramic + 10 µF tantalum local decoupling to suppress >100 MHz switching noise from output transitions. |
Key Features
| Feature | Design Value |
|---|---|
| Three enable inputs (G1, G2A, G2B) | Enables 24-line decoding without external inverters and simplifies hierarchical memory mapping in multi-bank architectures. |
| TTL-compatible input thresholds | VIH ≥ 2.0 V / VIL ≤ 0.8 V ensures reliable interfacing with legacy 74LS, 74F, and microcontroller GPIOs without level shifters. |
| Low ICC (80 µA max) | Reduces quiescent power in always-on subsystems such as missile guidance pre-arming circuits and satellite telemetry monitors. |
| 17 ns typical tpd @ 5.5 V | Meets timing closure requirements for 25-MHz synchronous bus cycles in MIL-STD-1553B interface controllers. |
| Military temperature range (−55°C to 125°C) | Validated for operation in jet engine bays, radar front-ends, and orbital payload bays without derating or thermal throttling. |
Applications
| Avionics Memory Decoding | Radar Signal Processor Addressing |
|---|---|
|
Use Scenario: Selecting one of eight SRAM banks in a flight control computer's real-time data buffer. IC Role / Device Role / Timing Role: 3-to-8 address decoder generating chip-select signals synchronized to 20-MHz clock domain. Use Value: 17 ns tpd ensures decoded CS asserts within 1.5 clock cycles, eliminating wait states in deterministic DO-254 compliant firmware. |
Use Scenario: Routing ADC sample streams to eight parallel DSP cores in an airborne synthetic aperture radar (SAR) processor. IC Role / Device Role / Timing Role: Demultiplexer using G1 as data input and A/B/C as channel ID - enabling time-sliced data distribution. Use Value: Matched output delays across Y0–Y7 prevent skew-induced phase errors in coherent SAR image reconstruction. |
| Missile Guidance Interface Logic | Satellite Telemetry Multiplexer |
|
Use Scenario: Enabling discrete analog sensor conditioning channels (gyro, accelerometer, baro) based on command word from guidance MCU. IC Role / Device Role / Timing Role: Enable-gated decoder asserting individual channel power-enable lines with fail-safe default-OFF behavior. Use Value: Triple-enable architecture (G1 HIGH + G2A/G2B LOW) prevents spurious activation during EMI transients on launch pad. |
Use Scenario: Selecting one of eight telemetry transmitters for downlink burst transmission in a CubeSat platform. IC Role / Device Role / Timing Role: Low-power address decoder driving enable pins of RF front-end ICs in radiation-hardened payload bay. Use Value: 1 µA max input current extends battery life during 72-hour deep-space coast phases between scheduled downlinks. |
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 |
|---|---|---|---|
| SNJ54HCT138J | Identical electrical specs and CDIP-J package; differs only in TI's internal part numbering convention (SNJ prefix denotes QML-38535 certified variant). | No functional difference; selected when formal QML certification documentation (e.g., lot traceability, radiation test reports) is contractually required. | Choose SNJ54HCT138J for DoD contracts mandating QML-38535 Class V or Class Q compliance. |
| SN54LS138J | Lower speed (tPD ≈ 25 ns), higher ICC (≈ 20 mA), TTL-input-only (no HCT compatibility), and narrower voltage range (4.75–5.25 V). | Used in legacy 74LS-based systems where backward compatibility outweighs power/performance gains. | Choose SN54LS138J only when replacing failed 74LS138 in fielded hardware with no redesign approval. |
Compared with SN54HCT138J, SNJ54HCT138J adds formal QML certification overhead without altering performance, while SN54LS138J trades 30% slower speed and 250× higher static power for guaranteed drop-in fit in vintage TTL designs - making SN54HCT138J the optimal balance of modern efficiency and military ruggedness.
Availability
SN54HCT138J is available at Aetrix Electronics and suitable for avionics memory decoding, radar signal processor addressing, missile guidance interface logic, and satellite telemetry multiplexing requiring stable component supply across extended temperature and long-lifecycle programs.
Supply support for SN54HCT138J 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 manufacturer founded in 1930, specializing in analog, embedded processing, and high-reliability logic solutions for aerospace, defense, and industrial markets.
The SN54HCT138J belongs to TI's military-grade HCT logic family, engineered specifically for high-speed memory decoding and data routing in mission-critical systems operating under extreme environmental stress.
FAQ
What is the maximum operating temperature range for SN54HCT138J?
The SN54HCT138J is rated for operation from −55°C to 125°C, fully qualified per MIL-PRF-38535 for use in engine compartments, radar front-ends, and space-rated electronics. This range is confirmed in the "Recommended Operating Conditions" table of TI's SCLS171E datasheet and validated through temperature cycling tests documented in TI's packaging addendum.
Does SN54HCT138J support demultiplexing functionality?
Yes, SN54HCT138J supports demultiplexing by using its enable inputs - particularly G1 (active-high) - as a data input while holding G2A/G2B LOW and applying address bits to A/B/C. This configuration routes a single input signal to one of eight outputs, as explicitly described in the "description/ordering information" section of the SCLS171E datasheet.
What is the typical propagation delay of SN54HCT138J at 5.5 V?
The typical propagation delay (tpd) of SN54HCT138J is 17 ns at VCC = 5.5 V and TA = 25°C, as specified in the "Switching Characteristics" table of the SCLS171E datasheet. This value applies to transitions from any address or enable input to any Yx output under CL = 50 pF loading conditions.
Can SN54HCT138J drive standard TTL loads directly?
Yes, SN54HCT138J can drive up to 10 LSTTL loads per output, as stated in the device description. Its ±4-mA output drive capability at 5 V meets the DC interface requirements of 74LSTTL inputs, eliminating the need for buffer stages in mixed-logic systems.
Is SN54HCT138J pin-compatible with SN74HCT138N?
Yes, SN54HCT138J and SN74HCT138N share identical pinout and logic function, both using 16-pin DIP footprints (J and N packages respectively). However, SN54HCT138J is rated for −55°C to 125°C and built in ceramic, while SN74HCT138N operates from −40°C to 85°C in plastic - making them functionally compatible but not environmentally interchangeable.
SN54HCT138J 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:
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- Qualification:
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- Supplier Device Package:
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SN54HCT138J FAQ
1.How can I place an order for SN54HCT138J through Aetrix?
Please submit a Request for Quotation (RFQ) for SN54HCT138J 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 SN54HCT138J reliable?
The price and inventory of SN54HCT138J are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN54HCT138J is usually 5 days.
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SN54HCT138J orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN54HCT138J 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 SN54HCT138J?
For technical support, including SN54HCT138J datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN54HCT138J requirements.
6.How does Aetrix verify that SN54HCT138J is sourced from the original manufacturer or authorized distributors?
All SN54HCT138J 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 SN54HCT138J meets industry standards.
7.What is the process for return or replacement of SN54HCT138J?
All SN54HCT138J units undergo pre-shipment inspection (PSI). If there is an issue with SN54HCT138J, 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 SN54HCT138J part is unused and in its original packaging.
Return procedure for SN54HCT138J:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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