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Texas Instruments SN74AHCT138QDRQ1
- Part No.:
- SN74AHCT138QDRQ1
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
SN74AHCT138QDRQ1.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:4,844
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Product details
Overview
SN74AHCT138QDRQ1 from Texas Instruments is an automotive-grade 3-line to 8-line decoder/demultiplexer with TTL-compatible inputs, 5.5 V absolute max supply rating, 12 ns typical propagation delay (CL = 15 pF), and AEC-Q100 qualification for operation from −40°C to +125°C. It enables high-speed memory decoding in engine control units and ADAS domain controllers.
For engineers reviewing the SN74AHCT138QDRQ1 datasheet, SN74AHCT138QDRQ1 pinout, SN74AHCT138QDRQ1 application, or SN74AHCT138QDRQ1 equivalent, key selection factors include its triple-enable architecture (G1, G2A, G2B), active-low/active-high enable mixing, automotive temperature range, SOIC-16 package compatibility, and 8-channel active-low decoded outputs.
Technical Context
This device implements a binary-select logic function where three address inputs (A, B, C) and three enable terminals (G1, G2A, G2B) jointly determine which of eight complementary outputs (Y0–Y7) is driven low. Its EPIC CMOS process ensures TTL-level input thresholds (VIH = 2 V min, VIL = 0.8 V max) while maintaining CMOS output drive capability.
Propagation delays are asymmetrically optimized: tPLH/tPHL from G1 is faster (9.1 ns typ) than from address lines (10.4 ns typ) under CL = 15 pF, supporting cascaded decoding schemes without external inverters - e.g., 24-line decoding uses two SN74AHCT138QDRQ1 devices with no added logic.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply voltage | 4.5 V to 5.5 V - compatible with standard 5 V automotive power rails and tolerant of transient overvoltage up to 7 V |
| Propagation delay | 6.6–12 ns - enables sub-100 MHz system clock synchronization in memory-mapped peripheral decoding |
| Output drive | ±8 mA - sufficient to directly drive multiple TTL inputs or small LED indicators without buffering |
| Input compatibility | TTL-voltage - accepts 0.8 V/2.0 V logic thresholds, eliminating level-shifting when interfacing legacy microcontrollers |
| Operating temperature | −40°C to +125°C - qualified per AEC-Q100 Grade 1 for under-hood and safety-critical automotive applications |
| ESD rating | ±2000 V HBM - exceeds MIL-STD-833 requirements for robustness in manufacturing and field environments |
| Power dissipation | 14 pF typical Cpd - supports low dynamic power in high-frequency address decoding at 1 MHz |
Pinout & Package
SN74AHCT138QDRQ1 is supplied in a 16-pin SOIC (D) package measuring 9.9 mm × 6.0 mm with 1.27 mm pitch. The body size is 9.9 mm × 3.9 mm. Thermal resistance RθJA is 73°C/W.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A | Select input A (LSB) | Binary address bit 0; determines least-significant output selection when enables are asserted |
| B | Select input B | Binary address bit 1; used with A and C to generate full 3-bit decode pattern |
| C | Select input C (MSB) | Binary address bit 2; MSB of 3-bit input controlling Y0–Y7 activation sequence |
| G2A | Active-low enable A | First enable input; must be LOW with G2B LOW and G1 HIGH for valid decode operation |
| G2B | Active-low enable B | Second enable input; both G2A and G2B must be LOW to activate decoder function |
| G1 | Active-high enable | Third enable input; must be HIGH alongside G2A/G2B LOW to enable output drive |
| Y0–Y7 | Active-low decoded outputs | Eight mutually exclusive outputs; only one is LOW per valid input combination; all HIGH otherwise |
| VCC | Positive supply | 5 V nominal supply connection; bypass capacitor (0.1 µF) required adjacent to pin for noise suppression |
| GND | Ground reference | Return path for all internal logic and output currents; requires low-impedance PCB plane connection |
Key Features
| Feature | Design Value |
|---|---|
| Triple-enable architecture | Supports seamless cascading of multiple decoders without external gates - e.g., 24-line decoding achieved with two devices |
| AEC-Q100 qualification | Validated for automotive use including extended temperature operation, ESD robustness, and latch-up immunity (>250 mA) |
| TTL-compatible inputs | Accepts standard 5 V TTL logic levels, enabling direct interface with legacy MCUs and FPGAs without level shifters |
| Low propagation delay | Sub-10 ns enable-to-output delay allows integration into high-speed memory subsystems where timing margin is critical |
| CMOS output structure | Delivers rail-to-rail swing and symmetrical drive strength (±8 mA), suitable for driving mixed-logic loads |
Applications
| Engine Control Unit (ECU) Memory Mapping | ADAS Domain Controller I/O Expansion |
|---|---|
Use Scenario: Decoding 3-bit address bus to select among eight peripheral registers (e.g., CAN transceivers, sensor ADCs, PWM timers) in a 32-bit RISC-based ECU. IC Role / Device Role / Timing Role: Address decoder providing chip-select signals with <12 ns propagation delay to meet tight memory-access timing budgets. Use Value: Eliminates need for discrete logic or FPGA resources, reducing BOM count and PCB area while maintaining deterministic decode latency. | Use Scenario: Enabling eight camera sensor interfaces or radar preprocessing modules via shared SPI/I²C buses in a centralized ADAS controller. IC Role / Device Role / Timing Role: Demultiplexer routing control signals to individual sensor subsystems using G1 as data-enable and A/B/C as channel index. Use Value: Enables single-master control of multiple sensors with minimal GPIO usage and guaranteed glitch-free channel selection. |
| Automotive Infotainment Display Backlight Control | Body Control Module (BCM) Relay Driver Matrix |
Use Scenario: Selecting one of eight backlight LED driver ICs in a multi-zone LCD display system based on brightness profile configuration. IC Role / Device Role / Timing Role: Decoder generating active-low enable pulses synchronized to PWM dimming signals for precise zone control. Use Value: Provides deterministic, low-jitter enable timing across zones, improving visual consistency and reducing EMI from simultaneous switching. | Use Scenario: Activating specific relay drivers (e.g., door lock actuators, window motors, mirror controls) in a distributed BCM using shared MCU GPIOs. IC Role / Device Role / Timing Role: Output demultiplexer converting 3-bit MCU port outputs into eight independent relay control lines. Use Value: Reduces required MCU I/O count by 5 pins versus direct drive, simplifying firmware and enabling reuse of limited GPIO resources. |
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 |
|---|---|---|---|
| SN74LV138AQPWRQ1 | Lower supply range (1.65–5.5 V), higher input threshold (VIH = 2.0 V min same), 13 ns max tPD at 3.3 V | Better suited for mixed-voltage 3.3 V systems; not drop-in for 5 V-only designs due to reduced noise margin at 5 V | Choose when migrating to lower-voltage domains or requiring wider VCC flexibility |
| MC74VHC138DT | Non-automotive grade, identical pinout and logic function, 11 ns max tPD at 5 V, no AEC-Q100 qualification | Lacks automotive qualification and extended temperature support; unsuitable for safety-critical or under-hood use | Select only for industrial or consumer prototypes where automotive reliability is not required |
Compared with SN74LV138AQPWRQ1 and MC74VHC138DT, SN74AHCT138QDRQ1 uniquely combines AEC-Q100 Grade 1 qualification, TTL-input compatibility at 5 V, and SOIC-16 footprint - making it the only option qualified for production automotive memory decoding where legacy interface and thermal robustness are mandatory.
Availability
SN74AHCT138QDRQ1 is available at Aetrix Electronics and suitable for engine control units, ADAS domain controllers, and automotive infotainment systems requiring stable component supply across long product lifecycles.
Supply support for SN74AHCT138QDRQ1 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 delivering analog, embedded processing, and connectivity solutions for automotive, industrial, and personal electronics markets.
The SN74AHCT138QDRQ1 belongs to TI's automotive logic portfolio, designed specifically for high-reliability decoding and signal routing in safety-critical vehicle subsystems operating across extreme ambient temperatures.
FAQ
What is the maximum supply voltage rating for SN74AHCT138QDRQ1?
The absolute maximum supply voltage for SN74AHCT138QDRQ1 is 7 V, though recommended operation is strictly between 4.5 V and 5.5 V per AEC-Q100 specifications. Exceeding 5.5 V during normal operation risks violating automotive reliability requirements, even if within absolute ratings. Always use regulated 5 V supplies with appropriate bypassing for SN74AHCT138QDRQ1.
Does SN74AHCT138QDRQ1 support cascading for larger decoding schemes?
Yes, SN74AHCT138QDRQ1 supports cascading via its three enable inputs (G1, G2A, G2B). Two devices can implement a 24-line decoder without external inverters, and three devices can achieve 32-line decoding with only one external inverter. This architecture reduces gate count and improves timing predictability compared to discrete logic solutions.
What is the output configuration of SN74AHCT138QDRQ1?
SN74AHCT138QDRQ1 provides eight active-low, open-drain–compatible outputs (Y0–Y7) with CMOS push-pull structure. Each output drives LOW when selected and HIGH (VCC) when deselected. Outputs are not internally clamped; external pull-ups are unnecessary unless interfacing with non-CMOS loads requiring defined HIGH states.
Is SN74AHCT138QDRQ1 pin-compatible with non-automotive versions like SN74AHCT138N?
Yes, SN74AHCT138QDRQ1 shares identical pinout, logic function, and electrical behavior with SN74AHCT138N (PDIP-16) and SN74AHCT138DR (SOIC-16), but adds AEC-Q100 qualification, extended temperature range (−40°C to +125°C), and automotive-specific reliability testing. No PCB changes are needed when upgrading from commercial-grade variants.
How should unused inputs be handled on SN74AHCT138QDRQ1?
All unused inputs on SN74AHCT138QDRQ1 must be tied to either VCC or GND to prevent floating nodes that cause increased ICC, noise susceptibility, or erratic output behavior. TI recommends tying unused address inputs (A/B/C) to GND and unused enables (G2A/G2B/G1) to inactive states - e.g., G1 to GND or G2A/G2B to VCC - per the function table in the datasheet.
SN74AHCT138QDRQ1 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74AHCT
- Package/Case:
- 16-SOIC (0.154", 3.90mm 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 ~ 125°C
- Grade:
- Automotive
- Qualification:
- AEC-Q100
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SOIC
SN74AHCT138QDRQ1 FAQ
1.How can I place an order for SN74AHCT138QDRQ1 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AHCT138QDRQ1 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 SN74AHCT138QDRQ1 reliable?
The price and inventory of SN74AHCT138QDRQ1 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AHCT138QDRQ1 is usually 5 days.
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Once your SN74AHCT138QDRQ1 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 SN74AHCT138QDRQ1?
For technical support, including SN74AHCT138QDRQ1 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AHCT138QDRQ1 requirements.
6.How does Aetrix verify that SN74AHCT138QDRQ1 is sourced from the original manufacturer or authorized distributors?
All SN74AHCT138QDRQ1 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 SN74AHCT138QDRQ1 meets industry standards.
7.What is the process for return or replacement of SN74AHCT138QDRQ1?
All SN74AHCT138QDRQ1 units undergo pre-shipment inspection (PSI). If there is an issue with SN74AHCT138QDRQ1, 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 SN74AHCT138QDRQ1 part is unused and in its original packaging.
Return procedure for SN74AHCT138QDRQ1:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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