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Texas Instruments SN74AHC138DBR
- Part No.:
- SN74AHC138DBR
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SSOP (0.209", 5.30mm Width)
- Datasheet:
-
SN74AHC138DBR.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16SSOP
- Quantity:
- Payment:
- Shipping:
Inventory:1,985
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Product details
Overview
SN74AHC138DBR from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in SSOP-16 package, operating from 2 V to 5.5 V, with propagation delays as low as 5.7 ns at 5 V and 15 pF load, designed for high-speed memory decoding and data-routing systems where minimal system delay is critical.
For engineers reviewing the SN74AHC138DBR datasheet, SN74AHC138DBR pinout, SN74AHC138DBR application, or SN74AHC138DBR equivalent, this page delivers verified electrical specs, functional truth table behavior, thermal resistance (82 °C/W), ESD ratings (2000 V HBM), and real-world cascading implementation guidance - all specific to the DB-package variant.
Technical Context
The SN74AHC138DBR implements active-high address select inputs (A0–A2) and three enable inputs (G1, G2A, G2B), two of which are active-low - enabling direct cascading of multiple units without external inverters. Its logic architecture supports both decoding (e.g., memory chip selection) and demultiplexing (e.g., routing one input to eight outputs) via enable-controlled output activation.
It uses advanced CMOS AHC technology, delivering rail-to-rail output swing, low ICC (≤40 μA), and input/output clamp current compliance per JESD 17 (≥250 mA). Switching characteristics are specified across 15 pF and 50 pF loads at both 3.3 V ±0.3 V and 5 V ±0.5 V supply conditions.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 2 V to 5.5 V - supports mixed-voltage system interfacing (e.g., 3.3 V logic driving 5 V peripherals) |
| tPLH / tPHL (5 V, 15 pF) | 5.7 ns max - enables use in sub-100 MHz address decode paths without adding timing budget overhead |
| IOH / IOL | ±8 mA at 5 V - sufficient to drive standard TTL loads or multiple CMOS inputs without buffering |
| ICC (max) | 40 μA at 5.5 V - ensures ultra-low static power in battery-backed or always-on control logic |
| ESD Rating (HBM) | 2000 V - meets industrial handling requirements without additional board-level protection |
| RθJA | 82 °C/W (SSOP-16) - defines thermal derating limit for continuous operation at ambient up to 85 °C |
Pinout & Package
SN74AHC138DBR is housed in a 16-pin SSOP (Shrink Small Outline Package) with 0.65 mm pitch, body size 6.2 mm × 7.8 mm, and thermal pad not present (unlike RGY/VQFN variants).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A0, A1, A2 | Address select inputs | Binary-encoded 3-bit address determining active output Y0–Y7; high-impedance when disabled |
| G1 | Active-high enable | Primary global enable; device inactive if low - used for hierarchical decoding or power gating |
| G2A, G2B | Active-low enables | Two independent active-low controls allow flexible cascade logic (e.g., G2A = /CS, G2B = /OE) |
| Y0–Y7 | Active-low decoded outputs | Only one output low per valid address/enable combination; all others remain high |
| VCC, GND | Power and ground | Must be decoupled locally; no internal regulation - requires stable 2–5.5 V supply |
Key Features
| Feature | Design Value |
|---|---|
| Three enable inputs (G1, G2A, G2B) | Enables 24-line decoding without external inverters and 32-line with only one inverter - reduces BOM count and layout area |
| Propagation delay ≤5.7 ns @ 5 V | Minimizes added latency in memory access paths - effective system delay becomes negligible versus typical SRAM access times |
| Latch-up immunity ≥250 mA | Ensures robustness against transient overcurrent events in noisy industrial environments without external current limiting |
| Input transition rate support | Rated for ≤20 ns/V at 5 V - accommodates fast-edge microcontroller GPIOs without signal integrity degradation |
| CMOS-compatible voltage thresholds | VIH = 3.85 V, VIL = 1.65 V @ VCC = 5.5 V - guarantees reliable interfacing with legacy 5 V TTL and modern mixed-signal MCUs |
Applications
| Memory Address Decoding | Peripheral Select Logic |
|---|---|
|
Use Scenario: Selecting one of eight SRAM or Flash memory chips in a microcontroller-based embedded system with limited address lines. IC Role / Device Role / Timing Role: Acts as a high-speed address decoder, translating 3-bit chip-select bus into individual /CE signals with sub-6 ns delay. Use Value: Eliminates need for discrete gate logic or FPGA resources; maintains tight timing margins even at 80+ MHz bus speeds. |
Use Scenario: Routing UART, SPI, or I²C signals to one of eight peripheral devices (e.g., sensors, DACs) on a shared bus. IC Role / Device Role / Timing Role: Functions as an active-low demultiplexer, using G1 as data-enable and A0–A2 as channel address. Use Value: Enables single-controller multi-peripheral communication without bus contention or software polling overhead. |
| Programmable Logic Interface | Industrial Control I/O Expansion |
|
Use Scenario: Generating enable signals for configurable logic blocks (e.g., CPLD configuration latches or FPGA I/O banks) based on mode register bits. IC Role / Device Role / Timing Role: Provides synchronous, glitch-free output selection synchronized to system clock edges via controlled enable sequencing. Use Value: Replaces custom PAL/GAL logic with pin-compatible, drop-in solution - simplifies firmware updates and design reuse. |
Use Scenario: Expanding discrete output capability of a PLC CPU module to drive eight solenoids, relays, or indicator LEDs. IC Role / Device Role / Timing Role: Serves as a buffered, current-capable output selector - each Yx drives up to 8 mA directly into LED/resistor loads. Use Value: Reduces external driver IC count; supports hot-swap-safe enable sequencing via G2A/G2B control. |
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 |
|---|---|---|---|
| SN74HC138DR | Slower propagation (19 ns @ 5 V), higher ICC (80 μA), same pinout and logic function | Acceptable for <20 MHz systems; less suitable for high-speed memory interfaces | Choose for cost-sensitive, lower-frequency designs where AHC speed is unnecessary |
| 74LVC138AD,118 | 3.3 V only (1.65–3.6 V), 5.5 ns max delay, 50 Ω output impedance, different pinout (SO-16) | Optimized for 3.3 V-only domains; requires level-shifting for 5 V compatibility | Prefer for modern low-voltage MCU platforms with strict power budgets and no 5 V requirement |
Compared with SN74HC138DR and 74LVC138AD,118, the SN74AHC138DBR uniquely balances 5 V tolerance, sub-6 ns speed, and SSOP packaging - making it the only choice for industrial controllers needing both legacy voltage compatibility and tight timing closure.
Availability
SN74AHC138DBR is available at Aetrix Electronics and suitable for high-speed memory decoding, peripheral multiplexing, programmable logic interfacing, and industrial I/O expansion requiring stable component supply across extended temperature ranges.
Supply support for SN74AHC138DBR 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 experience in high-reliability industrial and automotive-grade components.
The SN74AHC138DBR belongs to TI's AHC logic family, engineered for high-speed, low-power decoding and demultiplexing in memory subsystems and digital control architectures - emphasizing timing precision, noise immunity, and broad supply voltage operation.
FAQ
What is the maximum operating frequency supported by SN74AHC138DBR?
The SN74AHC138DBR does not specify a clock frequency but supports input transition rates up to 20 ns/V at 5 V. With propagation delays as low as 5.7 ns, it reliably operates in address decode paths up to ~80 MHz (based on worst-case setup/hold + delay margin). The SN74AHC138DBR is not a clocked device but a combinatorial decoder - its usable edge rate depends on system-level timing constraints, not an internal oscillator.
Can SN74AHC138DBR drive LEDs directly?
Yes - the SN74AHC138DBR provides ±8 mA output drive at 5 V, sufficient to sink current for standard 2 mA LEDs with appropriate series resistors. Each Yx output is active-low, so connecting LED anode to VCC and cathode to Yx enables direct drive. Do not exceed 8 mA per output or 75 mA total VCC/GND current, as specified in the absolute maximum ratings for SN74AHC138DBR.
Is SN74AHC138DBR pin-compatible with SN74HC138?
Yes - SN74AHC138DBR and SN74HC138 share identical pinout, function table, and package outline (SSOP-16). However, SN74AHC138DBR offers faster propagation (5.7 ns vs. 19 ns), lower ICC (40 μA vs. 80 μA), and improved noise margins. The SN74AHC138DBR can replace SN74HC138 in most designs unless legacy HC timing margins are tightly constrained.
Does SN74AHC138DBR require external pull-up resistors on outputs?
No - SN74AHC138DBR has push-pull outputs and does not require external pull-ups. Outputs actively drive high or low depending on decode state and enable conditions. Pull-ups are only needed if interfacing with open-drain systems or if a wired-OR function is required - which is not native to SN74AHC138DBR's architecture.
What is the meaning of "NRND" status for SN74AHC138DBR?
"NRND" (Not Recommended for New Designs) indicates TI no longer promotes SN74AHC138DBR for future projects, though it remains in production and supported. Aetrix Electronics maintains active inventory and supply chain continuity for SN74AHC138DBR to support legacy industrial and medical equipment where redesign is impractical or costly.
SN74AHC138DBR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74AHC
- 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:
- 2V ~ 5.5V
- Operating Temperature:
- -40°C ~ 85°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SSOP
SN74AHC138DBR FAQ
1.How can I place an order for SN74AHC138DBR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AHC138DBR 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 SN74AHC138DBR reliable?
The price and inventory of SN74AHC138DBR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AHC138DBR is usually 5 days.
3.What payment methods are accepted for SN74AHC138DBR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74AHC138DBR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74AHC138DBR?
SN74AHC138DBR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74AHC138DBR 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 SN74AHC138DBR?
For technical support, including SN74AHC138DBR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AHC138DBR requirements.
6.How does Aetrix verify that SN74AHC138DBR is sourced from the original manufacturer or authorized distributors?
All SN74AHC138DBR 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 SN74AHC138DBR meets industry standards.
7.What is the process for return or replacement of SN74AHC138DBR?
All SN74AHC138DBR units undergo pre-shipment inspection (PSI). If there is an issue with SN74AHC138DBR, 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 SN74AHC138DBR part is unused and in its original packaging.
Return procedure for SN74AHC138DBR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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