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Texas Instruments SN74AHCT138NG4
- Part No.:
- SN74AHCT138NG4
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74AHCT138NG4.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16DIP
- Quantity:
- Payment:
- Shipping:
Inventory:3,019
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Product details
Overview
SN74AHCT138NG4 from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in 16-pin PDIP (N) package, operating from 1.5 V to 5.5 V supply, with TTL-compatible inputs, 12 ns max propagation delay at 5 V/15 pF, and ±8 mA output drive-designed for high-speed memory decoding and address demultiplexing in industrial control and embedded microcontroller systems.
For engineers reviewing the SN74AHCT138NG4 datasheet, SN74AHCT138NG4 pinout, SN74AHCT138NG4 application, or SN74AHCT138NG4 equivalent, this page delivers verified functional modes, real-world timing behavior under load, thermal resistance (67 °C/W), latch-up immunity (>250 mA), and ESD robustness (±2000 V HBM) critical for reliable system integration.
Technical Context
The SN74AHCT138NG4 implements positive-logic 3-to-8 decoding with three enable inputs (G1 active-high; G2A/G2B active-low), enabling cascaded 24-line or 32-line decoding without external inverters. Its architecture supports both decoder and demultiplexer operation, where any enable input can serve as a data channel.
It uses advanced CMOS technology with TTL-voltage compatibility (VIH = 2 V, VIL = 0.8 V), ensuring interoperability with legacy 5 V logic families. Propagation delays are tightly specified across temperature (−40 °C to +85 °C) and supply (1.5–5.5 V), with switching characteristics validated at CL = 15 pF and CL = 50 pF loads.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage Range | 1.5 V to 5.5 V - supports mixed-voltage system interfacing and brown-out tolerant operation |
| Propagation Delay (tPLH/tPHL) | 1 ns min / 12 ns max at VCC = 5 V, CL = 15 pF - enables sub-83 MHz clock-domain routing in address decode paths |
| Output Drive Strength | ±8 mA at VOH/VOL - sufficient to directly drive multiple 74AHCT inputs or small LED indicators without buffers |
| Input Voltage Thresholds | VIH = 2.0 V, VIL = 0.8 V - ensures reliable recognition of standard TTL logic levels across voltage and temperature |
| Junction-to-Ambient Thermal Resistance | 67 °C/W (PDIP package) - allows sustained operation up to 85 °C ambient with minimal derating at full output loading |
| ESD Robustness | ±2000 V HBM, ±1000 V CDM - meets industrial IEC 61000-4-2 pre-compliance requirements for board-level handling |
| Latch-up Immunity | >250 mA per JESD17 - prevents destructive parasitic SCR activation during transient overcurrent events |
Pinout & Package
SN74AHCT138NG4 is housed in a 16-pin plastic dual in-line package (PDIP-N), body size 19.32 mm × 6.35 mm, with through-hole mounting and industry-standard 0.3-inch row spacing.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (A) | Binary Select Input A | LSB of 3-bit address; active HIGH; determines Y0–Y1 pair selection when enables are asserted |
| 2 (B) | Binary Select Input B | Mid-bit of 3-bit address; active HIGH; selects Y0–Y3 quadrant within enabled state |
| 3 (C) | Binary Select Input C | MSB of 3-bit address; active HIGH; selects Y0–Y7 octant when all enables active |
| 4 (G2A) | Strobe Input 2A | Active-LOW enable; must be LOW with G2B LOW and G1 HIGH for valid decode output |
| 5 (G2B) | Strobe Input 2B | Active-LOW enable; paired with G2A to form dual-active-low enable group |
| 6 (G1) | Strobe Input | Active-HIGH enable; completes 3-input enable logic (G1 AND NOT G2A AND NOT G2B) |
| 7 (Y7) | Active-LOW Output 7 | Complemented decoded output; LOW only when A=B=C=HIGH and all enables satisfied |
| 8 (GND) | Ground Reference | Primary return path for logic and output currents; requires low-impedance PCB connection |
| 9 (Y6) | Active-LOW Output 6 | Complemented decoded output; LOW only when A=LOW, B=HIGH, C=HIGH and enables active |
| 10 (Y5) | Active-LOW Output 5 | Complemented decoded output; LOW only when A=HIGH, B=LOW, C=HIGH and enables active |
| 11 (Y4) | Active-LOW Output 4 | Complemented decoded output; LOW only when A=B=LOW, C=HIGH and enables active |
| 12 (Y3) | Active-LOW Output 3 | Complemented decoded output; LOW only when A=LOW, B=HIGH, C=LOW and enables active |
| 13 (Y2) | Active-LOW Output 2 | Complemented decoded output; LOW only when A=HIGH, B=LOW, C=LOW and enables active |
| 14 (Y1) | Active-LOW Output 1 | Complemented decoded output; LOW only when A=LOW, B=C=LOW and enables active |
| 15 (Y0) | Active-LOW Output 0 | Complemented decoded output; LOW only when A=B=C=LOW and all enables satisfied |
| 16 (VCC) | Positive Supply | Power rail for internal logic and output drivers; requires local 0.1 µF ceramic bypass capacitor |
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 1.5–5.5 V supply-enables direct interface with legacy controllers without level shifters |
| Three Enable Inputs (G1, G2A, G2B) | Supports hierarchical decoding: two active-low (G2A/G2B) and one active-high (G1) enable allow seamless 24-line expansion without external inverters |
| Demultiplexer Capability | Any enable input (e.g., G1) can function as data input-converts 3-bit address + 1-bit data into eight individually gated outputs for signal routing |
| High-Speed Memory Decoding | Typical tPLH/tPHL = 7.6 ns at 5 V/15 pF-delays are shorter than typical fast SRAM access times, minimizing system-level address decode penalty |
| Robust Process Reliability | Latch-up immunity >250 mA per JESD17 and ESD ratings per JESD22-ensures survivability in manufacturing, test, and field-replaceable module environments |
Applications
| Memory Address Decoding | Microcontroller Peripheral Selection |
|---|---|
Use Scenario: Selecting one of eight SRAM or Flash memory banks in a 16-bit embedded system using A15–A13 as C–A inputs. IC Role / Device Role / Timing Role: 3-to-8 decoder mapping upper address bits to chip-select lines; operates synchronously with CPU bus cycle. Use Value: Eliminates need for discrete NAND gates or CPLD logic, reducing BOM count and layout area while maintaining <12 ns decode latency. |
Use Scenario: Routing UART, SPI, I²C, ADC, DAC, GPIO expander, timer, and CAN controller peripherals from an MCU with limited dedicated CS pins. IC Role / Device Role / Timing Role: Demultiplexer converting 3-bit peripheral ID + G1-as-data into individual enable signals; supports dynamic peripheral power gating. Use Value: Enables single MCU port to manage eight peripherals with deterministic, glitch-free selection via synchronous enable sequencing. |
| Industrial I/O Expansion | Legacy Bus Interface Logic |
Use Scenario: Controlling eight isolated relay drivers or optocoupled sensor inputs in PLC backplane modules using 24 V-tolerant level-shifted control lines. IC Role / Device Role / Timing Role: Address decoder translating microcontroller GPIO outputs into discrete channel enables; driven by buffered 5 V logic. Use Value: Provides noise-immune, current-limited (±8 mA) outputs compatible with 74AHCT-series buffer inputs, simplifying isolation stage design. |
Use Scenario: Adapting ISA or PC/104 bus address/data handshaking between modern low-voltage FPGAs and legacy 5 V peripheral cards. IC Role / Device Role / Timing Role: Level-translating decoder accepting TTL-compatible inputs and driving 5 V bus transceivers with precise timing alignment. Use Value: Maintains setup/hold margins on legacy bus cycles while supporting 1.8 V–5.5 V FPGA I/O domains via its wide VCC range. |
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 | Same logic function and pinout; HCT family has wider VCC range (2–6 V) but slower max speed (28 ns vs 12 ns at 5 V) | Suitable for cost-sensitive, non-critical timing applications where 5 V-only operation suffices | Select SN74HCT138DR only if propagation delay >20 ns is acceptable and 5 V supply is guaranteed |
| 74LV138PW | Lower voltage operation (1–5.5 V); LV family offers 10.5 ns max delay at 3.3 V but reduced drive (±6 mA) and no TTL input compatibility | Better for 3.3 V systems with tight power budgets; requires external level translation for TTL input sources | Choose 74LV138PW when optimizing for 3.3 V core logic and lower static current (<1 µA), not TTL interoperability |
Compared with SN74HCT138DR and 74LV138PW, the SN74AHCT138NG4 uniquely balances TTL input compatibility, 5.5 V tolerance, and 12 ns speed-making it optimal for mixed-voltage industrial designs requiring legacy interface fidelity without sacrificing performance.
Availability
SN74AHCT138NG4 is available at Aetrix Electronics and suitable for industrial control panels, embedded instrumentation, programmable logic interfaces, and legacy bus adapter modules requiring stable component supply and long-term manufacturability.
Supply support for SN74AHCT138NG4 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 over 50 years of innovation in high-reliability logic ICs for industrial and automotive markets.
The SN74AHCT138NG4 belongs to TI's AHCT logic family-engineered for TTL-compatible interfacing in high-speed memory and data-routing systems where propagation delay, noise immunity, and supply flexibility are critical.
FAQ
What is the maximum operating temperature for SN74AHCT138NG4?
The SN74AHCT138NG4 is rated for operation from −40 °C to +85 °C ambient temperature, matching the commercial temperature grade of the PDIP-N package. Its thermal resistance (RθJA = 67 °C/W) ensures reliable performance at full load within this range when properly heatsinked or mounted on standard FR-4 PCBs with adequate copper pour.
Does SN74AHCT138NG4 support 3.3 V logic systems?
Yes, SN74AHCT138NG4 operates from 1.5 V to 5.5 V and accepts TTL-compatible input thresholds (VIH = 2.0 V, VIL = 0.8 V), making it fully interoperable with 3.3 V microcontrollers and FPGAs. At VCC = 3.3 V, it delivers VOH ≥ 3.1 V and VOL ≤ 0.44 V under 8 mA load-meeting 3.3 V LVTTL output requirements.
Can SN74AHCT138NG4 be used as a demultiplexer?
Yes, SN74AHCT138NG4 functions as an 1-to-8 demultiplexer when one enable input (e.g., G1) is used as the data line and the remaining inputs (A, B, C, G2A, G2B) configure the address. The active-LOW outputs provide inverted demux functionality, commonly used in bus gating and signal routing applications.
What is the recommended bypass capacitor for SN74AHCT138NG4?
Texas Instruments recommends a 0.1 µF ceramic capacitor placed as close as possible to the VCC and GND pins of SN74AHCT138NG4. For enhanced high-frequency noise suppression, a parallel 1 µF tantalum or ceramic capacitor may be added-especially in systems with switching regulators or dense digital logic.
Is SN74AHCT138NG4 pin-compatible with other 74xx138 variants?
SN74AHCT138NG4 shares identical pinout and function with SN74HCT138, SN74LS138, and SN74LV138 in the 16-pin PDIP package. However, electrical differences-including input thresholds, output drive, and propagation delay-require validation in the target circuit before substitution.
SN74AHCT138NG4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74AHCT
- Package/Case:
- 16-DIP (0.300", 7.62mm)
- Packaging:
- Tube
- 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:
- Through Hole
- Supplier Device Package:
- 16-PDIP
SN74AHCT138NG4 FAQ
1.How can I place an order for SN74AHCT138NG4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AHCT138NG4 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 SN74AHCT138NG4 reliable?
The price and inventory of SN74AHCT138NG4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AHCT138NG4 is usually 5 days.
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SN74AHCT138NG4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74AHCT138NG4 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 SN74AHCT138NG4?
For technical support, including SN74AHCT138NG4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AHCT138NG4 requirements.
6.How does Aetrix verify that SN74AHCT138NG4 is sourced from the original manufacturer or authorized distributors?
All SN74AHCT138NG4 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 SN74AHCT138NG4 meets industry standards.
7.What is the process for return or replacement of SN74AHCT138NG4?
All SN74AHCT138NG4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74AHCT138NG4, 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 SN74AHCT138NG4 part is unused and in its original packaging.
Return procedure for SN74AHCT138NG4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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