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Texas Instruments SN74AHCT138DBRG4
- Part No.:
- SN74AHCT138DBRG4
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SSOP (0.209", 5.30mm Width)
- Datasheet:
-
SN74AHCT138DBRG4.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16SSOP
- Quantity:
- Payment:
- Shipping:
Inventory:4,871
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Product details
Overview
SN74AHCT138DBRG4 from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in SSOP-16 package, operating at 1.5–5.5 V supply, with TTL-compatible inputs, 12 ns max propagation delay (CL = 15 pF), and ±8 mA output drive-used for memory address decoding and data routing in industrial control and embedded microcontroller systems.
For engineers reviewing the SN74AHCT138DBRG4 datasheet, SN74AHCT138DBRG4 pinout, SN74AHCT138DBRG4 application, or SN74AHCT138DBRG4 equivalent, this page delivers verified electrical specs, functional mode truth table, thermal resistance (RθJA = 82°C/W), ESD ratings (±2000 V HBM), and real-world demultiplexing use cases without generic marketing language.
Technical Context
The SN74AHCT138DBRG4 implements positive-logic 3-to-8 decoding with three enable inputs: one active-high (G1) and two active-low (G2A, G2B), enabling hierarchical cascading for larger decoding schemes (e.g., 24-line or 32-line systems). Its architecture supports both decoder and demultiplexer modes-where an enable input serves as data input while select lines route it to one of eight outputs.
Designed for high-speed memory systems, it achieves sub-12 ns propagation delays under 5 V/15 pF conditions and maintains rail-to-rail output swing (VOH ≥ 3.8 V, VOL ≤ 0.5 V at IO = ±8 mA). Input thresholds (VIH = 2 V, VIL = 0.8 V) ensure robust TTL-level compatibility without level-shifting circuitry.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage | 1.5–5.5 V - supports mixed-voltage system interfacing (e.g., 3.3 V MCU driving 5 V peripherals) |
| Propagation Delay | 12 ns max (tPLH/tPHL, CL = 15 pF, VCC = 5 V) - enables timing-critical address decoding in ≤25 MHz memory buses |
| Output Drive | ±8 mA - sufficient to directly drive multiple 74-series logic inputs or small LED indicators without buffers |
| Input Compatibility | TTL voltage thresholds (VIH = 2 V, VIL = 0.8 V) - eliminates need for external level translators when interfacing legacy 5 V TTL sources |
| ESD Rating | ±2000 V HBM - meets industrial handling requirements per ANSI/ESDA/JEDEC JS-001 |
| Thermal Resistance | RθJA = 82°C/W (SSOP-16) - allows sustained operation at 85°C ambient with <100 mW power dissipation |
| Operating Temperature | −40°C to +85°C - qualified for commercial and industrial-grade embedded applications |
Pinout & Package
SN74AHCT138DBRG4 uses a 16-pin SSOP (Shrink Small Outline Package) with 0.65 mm lead pitch, body size 6.2 mm × 5.3 mm, and JEDEC MO-153 compliant footprint. Thermal performance is optimized for surface-mount reflow with NIPDAU lead finish and MSL Level-1 rating.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A, B, C | Binary Select Inputs | 3-bit address code determining which Y0–Y7 output is asserted low; active during valid enable condition |
| G1 | Active-High Enable | Primary chip-select signal; device enabled only when G1 = HIGH and both G2A/G2B = LOW |
| G2A, G2B | Active-Low Enables | Secondary enables allowing modular expansion-e.g., G2A tied to MSB of higher-order address bus |
| Y0–Y7 | Active-Low Outputs | One-of-eight decoded outputs driven LOW; all HIGH when disabled-supports wired-OR bus architectures |
| VCC, GND | Power & Ground | Single 1.5–5.5 V supply; requires local 0.1 µF ceramic bypass capacitor per TI layout guidelines |
Key Features
| Feature | Design Value |
|---|---|
| Three Enable Inputs | Enables hierarchical decoding (e.g., 24-line via two SN74AHCT138DBRG4 units) without external inverters |
| TTL-Compatible Inputs | Accepts standard 5 V TTL logic levels directly-no level-shifter needed in mixed-technology systems |
| Demultiplexer Mode | G1 or G2A can serve as data input while A/B/C select output path-reduces component count in serial-to-parallel conversion |
| Latch-Up Immunity | Exceeds 250 mA per JESD17-ensures robustness against transient current faults in noisy industrial environments |
| Low Input Capacitance | Ci = 10 pF max-minimizes loading on driving sources and preserves signal integrity in high-fanout buses |
Applications
| Memory Address Decoding | Microcontroller Peripheral Selection |
|---|---|
|
Use Scenario: Selecting one of eight SRAM or EPROM chips in a 64 KB memory map using upper address bits. IC Role / Device Role / Timing Role: 3-bit address decoder translating A13–A15 into chip-select signals with <12 ns latency. Use Value: Eliminates propagation delay penalty in critical memory access paths-keeps effective system access time within CPU specification. |
Use Scenario: Routing UART, SPI, or GPIO signals from a single microcontroller port to eight peripheral ICs (e.g., ADCs, DACs, sensors). IC Role / Device Role / Timing Role: Demultiplexer using G1 as data line and A/B/C as channel address-enabling time-division multiplexed I/O expansion. Use Value: Reduces required MCU GPIO count by 5 pins versus discrete enable lines; supports hot-swap-ready peripheral addressing. |
| Industrial Bus Arbitration | LED Matrix Row Driver |
|
Use Scenario: Managing shared CAN or RS-485 transceiver access across eight field devices on a common bus trunk. IC Role / Device Role / Timing Role: Active-low output enables individual transceivers while others remain high-impedance-preventing bus contention. Use Value: Ensures deterministic bus arbitration with zero cross-talk; leverages inherent Y0–Y7 HIGH-state isolation. |
Use Scenario: Driving rows of an 8×8 monochrome LED matrix where columns are scanned by microcontroller. IC Role / Device Role / Timing Role: Row-select decoder asserting one Yx output LOW per frame cycle to sink current from 8 LEDs simultaneously. Use Value: Delivers 8 mA per output-sufficient for direct LED drive at 5 mA typical; avoids external transistor arrays. |
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 | CMOS input thresholds (VIH = 3.15 V min), slower tPD = 21 ns (CL = 15 pF), lower ICC = 4 µA | Better for ultra-low-power battery systems but incompatible with 3.3 V TTL outputs without pull-ups | Choose SN74HC138DR only if supply is stable 4.5–6 V and speed <10 MHz suffices. |
| 74LVC138AD,118 | 3.3 V only (1.65–3.6 V), faster tPD = 5.2 ns, higher drive (±24 mA), different pinout (G1/G2A/G2B relocated) | Requires PCB redesign; superior for high-speed 3.3 V FPGA/CPU interfaces but not drop-in | Use 74LVC138AD,118 only in new 3.3 V designs prioritizing speed over legacy compatibility. |
Compared with SN74HC138DR and 74LVC138AD,118, the SN74AHCT138DBRG4 uniquely balances TTL compatibility, 5 V tolerance, and sub-12 ns speed-making it the only choice for retrofitting legacy 5 V systems requiring minimal layout change and guaranteed input recognition.
Availability
SN74AHCT138DBRG4 is available at Aetrix Electronics and suitable for industrial control panels, embedded memory subsystems, and programmable logic interface modules requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for SN74AHCT138DBRG4 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 with broad automotive, industrial, and communications portfolio coverage.
The SN74AHCT138DBRG4 belongs to TI's AHCT logic family-engineered for seamless integration between TTL and CMOS systems, emphasizing speed, noise immunity, and backward compatibility in legacy-upgrade and mixed-voltage applications.
FAQ
What is the maximum clock frequency supported by SN74AHCT138DBRG4 in demultiplexer mode?
The SN74AHCT138DBRG4 does not operate on a clock signal-it is asynchronous. Its usable switching rate depends on propagation delay and load capacitance. With CL = 15 pF and VCC = 5 V, tPD ≤ 12 ns supports reliable operation up to ≈40 MHz toggle rate in demux mode, assuming clean edges and proper termination.
Can SN74AHCT138DBRG4 drive LEDs directly without current-limiting resistors?
No. While SN74AHCT138DBRG4 outputs can sink up to 8 mA per pin, direct LED connection without series resistors risks exceeding absolute maximum ratings under varying VCC or forward voltage conditions. TI recommends a minimum 100 Ω resistor for 5 V operation to limit current to safe levels and ensure consistent brightness.
Is SN74AHCT138DBRG4 pin-compatible with SN74LS138N?
Yes-SN74AHCT138DBRG4 shares identical pinout and function table with SN74LS138N (16-pin DIP), including active-low outputs and three enable inputs. However, SN74AHCT138DBRG4 uses SSOP-16 packaging and operates at lower ICC, making it a direct functional replacement with improved speed and power efficiency-but requires PCB footprint adaptation.
Does SN74AHCT138DBRG4 require external pull-up resistors on its outputs?
No. SN74AHCT138DBRG4 features totem-pole outputs capable of actively driving HIGH (VOH ≥ 3.8 V at IOH = −8 mA) and LOW (VOL ≤ 0.5 V at IOL = 8 mA). Pull-ups are unnecessary unless implementing wired-OR logic or open-drain emulation-per TI's recommended usage in standard decoder applications.
What is the thermal pad configuration for SN74AHCT138DBRG4?
SN74AHCT138DBRG4 in SSOP-16 (DB) package has no exposed thermal pad. Thermal management relies on copper pour under the leads and standard PCB trace width design per IPC-2221. The RθJA value of 82°C/W assumes JEDEC-standard 2S2P board layout with 1 in² 2 oz copper area beneath the package.
SN74AHCT138DBRG4 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:
- Discontinued at Digi-Key
- 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
SN74AHCT138DBRG4 FAQ
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6.How does Aetrix verify that SN74AHCT138DBRG4 is sourced from the original manufacturer or authorized distributors?
All SN74AHCT138DBRG4 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 SN74AHCT138DBRG4 meets industry standards.
7.What is the process for return or replacement of SN74AHCT138DBRG4?
All SN74AHCT138DBRG4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74AHCT138DBRG4, 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 SN74AHCT138DBRG4 part is unused and in its original packaging.
Return procedure for SN74AHCT138DBRG4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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