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Texas Instruments SN74AHCT138DBR
- Part No.:
- SN74AHCT138DBR
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SSOP (0.209", 5.30mm Width)
- Datasheet:
-
SN74AHCT138DBR.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16SSOP
- Quantity:
- Payment:
- Shipping:
Inventory:3,992
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Product details
Overview
SN74AHCT138DBR from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in SSOP-16 package, designed for high-speed memory decoding and data-routing applications. It features TTL-voltage-compatible inputs (VIH = 2 V, VIL = 0.8 V), propagation delays as low as 1 ns at 5 V with 15 pF load, and three enable inputs (G1 active-high, G2A/G2B active-low) enabling cascaded 24- or 32-line decoding without external inverters.
For engineers reviewing the SN74AHCT138DBR datasheet, SN74AHCT138DBR pinout, SN74AHCT138DBR application, or SN74AHCT138DBR equivalent, this page delivers verified electrical specs, functional mode details, real-world use cases in memory systems and address decoding, and validated alternative options for design continuity.
Technical Context
The SN74AHCT138DBR implements positive-logic 3-to-8 decoding with active-low outputs (Y0–Y7), where selection is determined by binary inputs A, B, C and three strobe enables (G1, G2A, G2B). Its function table defines eight mutually exclusive output states when all enables are asserted - one output goes LOW while others remain HIGH.
It operates across 1.5 V to 5.5 V supply range with guaranteed TTL input compatibility, supports demultiplexing via enable-as-data-input capability, and meets JESD 17 latch-up immunity (>250 mA) and JESD 22 ESD ratings (±2000 V HBM, ±1000 V CDM).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage (VCC) | 1.5 V to 5.5 V - ensures interoperability with mixed-voltage logic systems including 3.3 V and 5 V buses. |
| Propagation Delay (tPLH/tPHL) | 1 ns min / 12 ns max at 5 V, CL = 15 pF - enables sub-100 MHz address decoding in high-speed memory subsystems. |
| Output Drive (IOL/IOH) | ±8 mA - sufficient to directly drive multiple 74AHCT inputs or small capacitive loads without buffering. |
| Input Thresholds (VIH/VIL) | VIH = 2.0 V, VIL = 0.8 V - guarantees reliable recognition of standard TTL logic levels across temperature (−40°C to +85°C). |
| Power Dissipation Capacitance (Cpd) | 14 pF - quantifies dynamic power consumption during switching; used with frequency to calculate ICC dynamic component. |
| ESD Protection | ±2000 V HBM, ±1000 V CDM - exceeds JEDEC standards for robust handling in automated assembly and field environments. |
Pinout & Package
SN74AHCT138DBR uses a 16-pin SSOP (Shrink Small Outline Package) with 0.65 mm pitch, body size 6.2 mm × 5.3 mm, and thermal pad omitted (non-exposed). Pin 1 is marked by a beveled corner or dot; device orientation follows JEDEC standard top-view layout.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A (Pin 1) | Binary Select Input | LSB of 3-bit address; determines output Y0–Y7 mapping when enables are active. |
| B (Pin 2) | Binary Select Input | Middle bit of address; combined with A and C to select one of eight decoded lines. |
| C (Pin 3) | Binary Select Input | MSB of address; completes 3-bit decode vector for full 8-output selection. |
| G2A (Pin 4) | Strobe Enable Input | Active-low enable; must be LOW with G2B and G1 to activate decoding function. |
| G2B (Pin 5) | Strobe Enable Input | Second active-low enable; both G2A and G2B must be LOW for device operation. |
| G1 (Pin 6) | Strobe Enable Input | Active-high enable; provides asymmetric enable control ideal for hierarchical decoding trees. |
| Y7 (Pin 7) | Active-Low Output | Complement of decoded state "111"; sinks current when selected, remains HIGH otherwise. |
| GND (Pin 8) | Ground Reference | Primary return path for all internal logic and output currents; requires low-inductance connection. |
| Y6 (Pin 9) | Active-Low Output | Complement of "110"; used in address decoding for memory bank 6 or peripheral select. |
| Y5 (Pin 10) | Active-Low Output | Complement of "101"; commonly assigned to I/O port or interrupt controller enable. |
| Y4 (Pin 11) | Active-Low Output | Complement of "100"; supports chip-select generation for flash or SRAM devices. |
| Y3 (Pin 12) | Active-Low Output | Complement of "011"; used in bus arbitration or peripheral multiplexing schemes. |
| Y2 (Pin 13) | Active-Low Output | Complement of "010"; enables timing-critical peripherals requiring fast enable assertion. |
| Y1 (Pin 14) | Active-Low Output | Complement of "001"; often tied to reset or configuration logic in embedded controllers. |
| Y0 (Pin 15) | Active-Low Output | Complement of "000"; default boot device select line in microcontroller-based systems. |
| VCC (Pin 16) | Positive Supply | Logic supply input; requires local 0.1 µF ceramic bypass capacitor placed within 3 mm of pin. |
Key Features
| Feature | Design Value |
|---|---|
| TTL-voltage compatible inputs | Accepts standard 5 V TTL logic thresholds (VIH ≥ 2 V, VIL ≤ 0.8 V) while operating from 3.3 V or 5 V supplies - eliminates level-shifter requirements in mixed-voltage designs. |
| Three independent enable inputs | G1 (active-high), G2A/G2B (active-low) allow flexible cascading: 24-line decoding without inverters; 32-line with only one external inverter - reduces board area and component count. |
| Sub-12 ns propagation delay | Guaranteed tPLH/tPHL ≤ 12 ns at 5 V, 15 pF enables integration into memory subsystems with ≤10 ns access times - minimizes added system latency. |
| JESD 17 latch-up immunity | Exceeds 250 mA - prevents destructive latch-up during transient overvoltage events in industrial or automotive environments with noisy power rails. |
| SSOP-16 RoHS-compliant packaging | 6.2 mm × 5.3 mm body, 0.65 mm pitch, NIPDAU lead finish, MSL Level-1 - supports high-density PCB layouts and lead-free reflow assembly without moisture sensitivity concerns. |
Applications
| Memory Address Decoding | Peripheral Selection Logic |
|---|---|
Use Scenario: Selecting one of eight SRAM or flash memory chips in a 64 KB system using A15–A13 as inputs and chip-enable signals as outputs. IC Role / Device Role / Timing Role: 3-to-8 decoder generating active-low chip-select (CS#) signals synchronized to address bus transitions. Use Value: Eliminates discrete gate logic; propagation delay <12 ns ensures CS# assertion aligns with memory access window under 5 V operation. |
Use Scenario: Routing CPU address/data bus to UART, SPI, I²C, or GPIO expanders on an industrial controller PCB. IC Role / Device Role / Timing Role: Demultiplexer converting 3-bit peripheral ID into dedicated enable lines, with G1 used as data strobe. Use Value: Enables single-cycle peripheral activation; TTL-compatible inputs interface directly with microcontroller GPIO without level translation. |
| Bus Arbitration Control | FPGA Configuration Interface |
Use Scenario: Managing shared resource access among four DMA channels and two interrupt controllers in a real-time embedded system. IC Role / Device Role / Timing Role: Priority encoder companion providing mutually exclusive enable signals based on request bus state. Use Value: Three enable inputs allow hierarchical arbitration: G2A/B gated by master priority, G1 controlled by scheduler - no external glue logic needed. |
Use Scenario: Sequencing configuration bitstreams to multiple Xilinx Spartan or Intel MAX II CPLDs during power-up. IC Role / Device Role / Timing Role: Boot-mode selector asserting CONFIG_EN# for specific FPGA while holding others in reset. Use Value: Active-low outputs match FPGA reset/enable polarity; 8 mA drive strength reliably pulls down FPGA configuration pins without pull-up conflicts. |
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 |
|---|---|---|---|
| SN74HCT138DR | SOIC-16 package; identical logic, timing, and DC specs; RθJA = 93.8°C/W vs. DBR's 82°C/W. | Larger footprint (9.9 mm × 6 mm); less suitable for space-constrained boards but easier for manual soldering and prototyping. | Select when board layout prioritizes assembly simplicity over density, or when legacy SOIC footprints are fixed. |
| 74LV138PW | Lower voltage range (1.0–5.5 V); 3.3 V optimized; tPLH/tPHL = 10.5 ns max at 3.3 V; IOH/IOL = ±6 mA. | Better for battery-powered or low-power systems; not TTL-compatible - requires level-shifting if interfacing with 5 V microcontrollers. | Choose for energy-sensitive applications where 5 V TTL compatibility is unnecessary and 3.3 V operation dominates. |
Compared with SN74HCT138DR and 74LV138PW, the SN74AHCT138DBR uniquely balances TTL input compatibility, SSOP density, and 5 V memory-system timing - making it optimal for industrial controllers and legacy-compatible embedded designs where signal integrity and board space are co-constrained.
Availability
SN74AHCT138DBR is available at Aetrix Electronics and suitable for industrial control panels, medical diagnostic equipment, and test instrumentation requiring stable component supply across extended temperature ranges (−40°C to +85°C) and long production lifecycles.
Supply support for SN74AHCT138DBR 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 specializing in analog, embedded processing, and logic solutions, with decades of heritage in industry-standard logic families.
The SN74AHCT138DBR belongs to TI's AHCT logic series, engineered for TTL-compatible operation in high-speed memory and data-path applications where low propagation delay and robust noise immunity are critical.
FAQ
What is the maximum clock frequency supported by SN74AHCT138DBR in demultiplexing mode?
The SN74AHCT138DBR does not operate on a clock signal - it is a combinational logic device. Its usable frequency depends on propagation delay and load capacitance. With tPHL/tPLH ≤ 12 ns and CL = 15 pF, it supports address/data bus switching up to approximately 40 MHz in worst-case timing paths, assuming clean edges and proper termination.
Can SN74AHCT138DBR be operated from a 3.3 V supply while interfacing with 5 V TTL devices?
Yes. The SN74AHCT138DBR accepts TTL-level inputs (VIH ≥ 2.0 V, VIL ≤ 0.8 V) across its full 1.5–5.5 V VCC range. At 3.3 V supply, VOH ≈ 3.8 V and VOL ≈ 0.36 V (IOL = 8 mA), which meets 5 V TTL input thresholds - enabling direct connection to legacy 5 V peripherals without level shifters.
How should unused inputs be handled on SN74AHCT138DBR to prevent malfunction?
All unused inputs - including A, B, C, G1, G2A, and G2B - must be tied to a valid logic level. Connect unneeded select lines (A/B/C) to GND or VCC to fix output states; tie unused enables to inactive levels (G1 to GND, G2A/G2B to VCC) to disable the device. Floating inputs cause undefined outputs and increased ICC.
Is SN74AHCT138DBR pin-compatible with other 74-series 138 decoders in SSOP package?
Yes. SN74AHCT138DBR shares identical pinout, function, and package dimensions with SN74HCT138DBR and SN74ACT138DBR. Differences lie only in AC/DC specifications (e.g., drive strength, propagation delay, noise margins), so substitution requires verification against timing and voltage margin requirements.
Does SN74AHCT138DBR include built-in ESD protection, and what standards does it meet?
Yes. The SN74AHCT138DBR exceeds JESD 22 ESD ratings: ±2000 V human-body model (HBM) and ±1000 V charged-device model (CDM). These values are production-tested and ensure robustness during handling, PCB assembly, and field operation in typical industrial environments.
SN74AHCT138DBR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74AHCT
- Package/Case:
- 16-SSOP (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:
- 8mA, 8mA
- Voltage Supply Source:
- Single Supply
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- -40°C ~ 85°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SSOP
SN74AHCT138DBR FAQ
1.How can I place an order for SN74AHCT138DBR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AHCT138DBR 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 SN74AHCT138DBR reliable?
The price and inventory of SN74AHCT138DBR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AHCT138DBR is usually 5 days.
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SN74AHCT138DBR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74AHCT138DBR 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 SN74AHCT138DBR?
For technical support, including SN74AHCT138DBR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AHCT138DBR requirements.
6.How does Aetrix verify that SN74AHCT138DBR is sourced from the original manufacturer or authorized distributors?
All SN74AHCT138DBR 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 SN74AHCT138DBR meets industry standards.
7.What is the process for return or replacement of SN74AHCT138DBR?
All SN74AHCT138DBR units undergo pre-shipment inspection (PSI). If there is an issue with SN74AHCT138DBR, 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 SN74AHCT138DBR part is unused and in its original packaging.
Return procedure for SN74AHCT138DBR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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