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Texas Instruments SN74AHC138N-P2
- Part No.:
- SN74AHC138N-P2
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74AHC138N-P2.pdf
- Description:
- SN74AHC138 3-LINE TO 8-LINE DECO
- Quantity:
- Payment:
- Shipping:
Inventory:4,400
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Product details
Overview
SN74AHC138N-P2 from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in 16-pin PDIP package, operating from 2 V to 5.5 V, with propagation delays as low as 5.7 ns (VCC = 5 V, CL = 15 pF), ±8 mA output drive, and three enable inputs (G1, G2A, G2B) for cascading in memory decoding systems.
For engineers reviewing the SN74AHC138N-P2 datasheet, SN74AHC138N-P2 pinout, SN74AHC138N-P2 application, or SN74AHC138N-P2 equivalent, key selection criteria include active-low dual-enable + active-high enable architecture, guaranteed 250 mA latch-up immunity per JESD 17, and compatibility with high-speed address decoding in industrial control and embedded logic subsystems.
Technical Context
The SN74AHC138N-P2 implements combinational logic decoding using three binary select inputs (A, B, C) and three independent enables (G1 high-active, G2A/G2B low-active), allowing flexible demultiplexing or hierarchical decoding without external inverters. Its TTL-compatible input thresholds and CMOS output structure support mixed-voltage interfacing across 2–5.5 V operation.
Propagation delay is symmetric across all input-to-output paths (tPLH/tPHL ≤ 9.5 ns at VCC = 5 V, CL = 15 pF), and output drive capability (±8 mA at VCC = 5 V) ensures robust fanout into standard AHC/AHCT loads while maintaining rail-to-rail VOH/VOL performance under load.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 2 V to 5.5 V - supports direct interface with 3.3 V and 5 V logic domains without level shifters |
| Propagation Delay (max) | 9.5 ns at VCC = 5 V, CL = 15 pF - enables use in sub-100 MHz address decode timing paths |
| Output Drive | ±8 mA at VCC = 5 V - drives ≥10 AHC loads or ≥4 LVTTL inputs with margin |
| Enable Architecture | G1 (active-high), G2A/G2B (active-low) - permits 24-line decoding without external inverters |
| Latch-Up Immunity | >250 mA per JESD 17 - meets industrial reliability requirements for sustained overcurrent events |
| ESD Rating | 2000-V HBM, 200-V MM, 1000-V CDM - exceeds JEDEC standards for handling and board-level robustness |
Pinout & Package
SN74AHC138N-P2 uses a 16-pin plastic dual in-line package (PDIP-N) with 0.3-inch body width and through-hole mounting. Pin 1 is located at the left end of the top row when viewed from the top with notch or dot oriented upward.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (G2A) | Active-low enable input | Must be low to activate decoding; used with G2B and G1 to gate all outputs |
| 2 (G2B) | Active-low enable input | Second low-enable; both G2A and G2B must be low for function enable |
| 3 (G1) | Active-high enable input | Must be high to enable; complements dual low-enables for flexible cascade control |
| 4 (C) | MSB address input | Third select bit; combined with B and A determines active Yx output |
| 5 (B) | Address input | Second select bit; forms 3-bit binary code selecting one of eight outputs |
| 6 (A) | LSB address input | First select bit; full A:B:C combination selects Y0–Y7 uniquely |
| 7 (Y0) | Active-low decoded output | Low only when G1=H, G2A=L, G2B=L, and A=B=C=L; all other outputs high |
| 8 (GND) | Ground reference | Return path for all internal logic and output currents; requires low-impedance PCB connection |
| 9 (Y1) | Active-low decoded output | Low when A=L, B=L, C=H; matches binary 001; inverted output logic |
| 10 (Y2) | Active-low decoded output | Low when A=L, B=H, C=L; matches binary 010; supports octal address expansion |
| 11 (Y3) | Active-low decoded output | Low when A=L, B=H, C=H; enables 4-device 32-line decode with one external inverter |
| 12 (Y4) | Active-low decoded output | Low when A=H, B=L, C=L; used in memory chip-select generation for 8-bank systems |
| 13 (Y5) | Active-low decoded output | Low when A=H, B=L, C=H; provides dedicated enable for peripheral I/O decoding |
| 14 (Y6) | Active-low decoded output | Low when A=H, B=H, C=L; supports interrupt vector routing in microcontroller systems |
| 15 (Y7) | Active-low decoded output | Low only when A=B=C=H; final output in 3-to-8 decode sequence; used for highest-address bank |
| 16 (VCC) | Supply voltage | Power rail for internal logic and output drivers; bypass capacitor required near pin |
Key Features
| Feature | Design Value |
|---|---|
| Three enable inputs (G1, G2A, G2B) | Enables 24-line decoding without external inverters and 32-line with one inverter - reduces component count in multi-chip memory systems |
| High-speed propagation (5.7 ns typ) | Meets tight timing budgets in 5 V high-performance memory subsystems where decoder delay must be < memory access time |
| Wide VCC range (2–5.5 V) | Allows single part to serve both 3.3 V FPGA I/O banks and legacy 5 V microcontroller buses without voltage translation |
| Guaranteed latch-up immunity (>250 mA) | Ensures robust operation in industrial environments with transient ground bounce or supply coupling |
| Industry-standard PDIP-16 footprint | Supports manual prototyping, socket-based testing, and legacy through-hole manufacturing without redesign |
Applications
| Memory Address Decoding | Peripheral Select Logic |
|---|---|
Use Scenario: Decoding 3-bit address bus to generate eight independent chip-select signals for SRAM, Flash, or EEPROM devices in an 8051 or ARM7-based controller. IC Role / Device Role / Timing Role: Primary address decoder providing active-low chip-select outputs synchronized to address valid timing with sub-10 ns delay. Use Value: Eliminates need for discrete NAND gates or additional inverters in 8-device memory maps, reducing BOM cost and layout area by up to 30%. | Use Scenario: Routing UART, SPI, or GPIO peripheral enables in a programmable logic controller (PLC) backplane with fixed I/O slot addressing. IC Role / Device Role / Timing Role: Demultiplexer converting processor address lines into individual peripheral enable asserts with deterministic setup/hold timing. Use Value: Enables hot-swappable I/O module detection via G2A/G2B gating, supporting modular system expansion without firmware changes. |
| Interrupt Vector Mapping | Industrial Control Bus Expansion |
Use Scenario: Assigning priority-encoded interrupt request lines from multiple sensors (temperature, pressure, flow) to a single MCU IRQ pin using encoded address bits. IC Role / Device Role / Timing Role: Priority encoder front-end generating unique vector addresses based on sensor ID inputs A/B/C and enable status. Use Value: Reduces MCU interrupt latency by 12 ns versus software polling, meeting <50 µs real-time response requirements in motion control. | Use Scenario: Expanding 4-bit control bus to drive 8 solenoid valves or relay drivers in HVAC or factory automation panels. IC Role / Device Role / Timing Role: Logic-level translator and fanout buffer converting microcontroller GPIO outputs into isolated, current-sink capable valve controls. Use Value: Provides ±8 mA sink per output - sufficient to directly drive ULN2003A inputs without series resistors, simplifying driver stage design. |
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 |
|---|---|---|---|
| SN74LV138A | Lower VCC range (1.65–5.5 V); 12 ns max tPD at 3.3 V; higher input capacitance (4.5 pF vs 2 pF) | Better suited for battery-powered 1.8 V systems but slower in 5 V high-speed decoding | Select SN74LV138A only when operating below 2 V or requiring enhanced 1.8 V compatibility |
| 74HC138 | Slower propagation (24 ns max at 4.5 V); lower drive (±4 mA); no specified latch-up rating | Acceptable for low-frequency control logic but not for memory subsystems requiring <10 ns timing margin | Choose 74HC138 only in cost-sensitive, non-critical timing applications where speed is not constrained |
Compared with SN74LV138A and 74HC138, SN74AHC138N-P2 delivers the shortest propagation delay and strongest latch-up immunity in the AHC family, making it the preferred choice for industrial memory decoding where timing margin and reliability are critical.
Availability
SN74AHC138N-P2 is available at Aetrix Electronics and suitable for industrial control, embedded instrumentation, and legacy system repair requiring stable component supply and through-hole manufacturability.
Supply support for SN74AHC138N-P2 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 high-reliability logic families.
The SN74AHC138N-P2 belongs to TI's Advanced High-Speed CMOS (AHC) logic series, engineered for high-performance memory decoding and data-routing applications demanding minimal propagation delay and robust noise immunity.
FAQ
What is the maximum operating frequency supported by SN74AHC138N-P2 in a memory decode application?
The SN74AHC138N-P2 does not specify a clock frequency since it is a combinational device, but its 5.7 ns typical propagation delay at VCC = 5 V enables reliable operation in systems with address valid windows ≥10 ns. In practice, it supports memory access cycles up to 80 MHz when paired with fast SRAM (e.g., CY62167EV30) where decoder delay is less than the memory's access time. The SN74AHC138N-P2 must be used with proper input slew rate control (≤20 ns/V at 5 V) to maintain timing integrity.
Can SN74AHC138N-P2 be used with 3.3 V microcontrollers without level shifting?
Yes, SN74AHC138N-P2 operates from 2 V to 5.5 V and has TTL-compatible input thresholds (VIH = 2.1 V min at VCC = 3 V), making it fully interoperable with 3.3 V microcontrollers such as the STM32F103 or PIC18F45K22. Its outputs swing rail-to-rail (VOH ≥ 2.48 V, VOL ≤ 0.5 V at VCC = 3 V, IOL = 4 mA), ensuring noise margins >0.7 V for downstream AHC or LVC inputs. No level shifter is needed when VCC = 3.3 V.
How many SN74AHC138N-P2 devices are required to decode a 5-bit address bus into 32 discrete outputs?
A single SN74AHC138N-P2 decodes 3 bits into 8 outputs. To decode 5 bits (32 outputs), four SN74AHC138N-P2 devices are required: three configured for 24-line decoding using only G1 and G2A/G2B enables (no external inverters), and one additional SN74AHC138N-P2 driven by the upper two address bits plus an inverter on one enable line to generate the remaining 8 outputs - matching Figure 3 in the SN74AHC138 datasheet. All enable logic remains within the SN74AHC138N-P2 family.
Does SN74AHC138N-P2 support hot insertion or live circuit replacement?
No, SN74AHC138N-P2 is not designed for hot insertion. Its absolute maximum ratings do not include powered-insertion stress conditions, and the PDIP package lacks hot-swap protection features such as power-on reset or slew-limited I/O. Applying VCC or signal voltages before establishing GND can cause latch-up or ESD damage. For live-replaceable systems, use hot-swap controllers (e.g., TPS23754) upstream of the SN74AHC138N-P2 supply rail.
What is the thermal resistance (θJA) of SN74AHC138N-P2 in its PDIP package?
The junction-to-ambient thermal resistance (θJA) for SN74AHC138N-P2 in the PDIP-N package is 67°C/W, measured under standard JEDEC test conditions (single-layer 1-in² copper pad, no airflow). This value assumes minimal PCB copper; actual θJA improves to ~45°C/W with 2-in² internal ground plane and 1 oz copper. At 8 mA output current per pin and 5 V supply, worst-case power dissipation is <25 mW, resulting in negligible junction temperature rise (<2°C) in typical industrial ambient conditions.
SN74AHC138N-P2 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- -
- Package/Case:
- 16-DIP (0.300", 7.62mm)
- Packaging:
- Bulk
- Product Status:
- Obsolete
- 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:
- Through Hole
- Supplier Device Package:
- 16-PDIP
SN74AHC138N-P2 FAQ
1.How can I place an order for SN74AHC138N-P2 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AHC138N-P2 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 SN74AHC138N-P2 reliable?
The price and inventory of SN74AHC138N-P2 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AHC138N-P2 is usually 5 days.
3.What payment methods are accepted for SN74AHC138N-P2?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74AHC138N-P2 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74AHC138N-P2?
SN74AHC138N-P2 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74AHC138N-P2 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 SN74AHC138N-P2?
For technical support, including SN74AHC138N-P2 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AHC138N-P2 requirements.
6.How does Aetrix verify that SN74AHC138N-P2 is sourced from the original manufacturer or authorized distributors?
All SN74AHC138N-P2 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 SN74AHC138N-P2 meets industry standards.
7.What is the process for return or replacement of SN74AHC138N-P2?
All SN74AHC138N-P2 units undergo pre-shipment inspection (PSI). If there is an issue with SN74AHC138N-P2, 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 SN74AHC138N-P2 part is unused and in its original packaging.
Return procedure for SN74AHC138N-P2:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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