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Texas Instruments CD74AC138ME4
- Part No.:
- CD74AC138ME4
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
CD74AC138ME4.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:4,586
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Product details
Overview
CD74AC138ME4 from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in a 16-pin PDIP package, operating from 1.5 V to 5.5 V with ±24 mA output drive, balanced propagation delays, and SCR-latchup-resistant CMOS process. It features three enable inputs (G1, G2A, G2B) for cascading and is designed for high-speed memory decoding and data-routing systems.
For engineers reviewing the CD74AC138ME4 datasheet, CD74AC138ME4 pinout, CD74AC138ME4 application, or CD74AC138ME4 equivalent, key selection criteria include its 10 ns max propagation delay at 5 V, 3-state outputs, ESD rating of ±2000 V HBM, and compatibility with legacy TTL and CMOS logic families in industrial control and embedded memory interfaces.
Technical Context
The CD74AC138ME4 implements positive-logic 3-to-8 decoding with active-low enable architecture: all three strobes (G1, G2A, G2B) must be asserted (G1 = high, G2A = G2B = low) for valid output selection. Its Schmitt-trigger inputs are absent - only standard CMOS inputs are specified per functional block diagram and pin table.
Propagation delay is input-dependent: tPLH/tPHL from address inputs (A/B/C) is 11 ns max at VCC = 5 V, while enable inputs (G1, G2A/G2B) exhibit faster 10 ns max delay under identical conditions. Output drive capability remains stable across –55°C to 125°C ambient, supporting industrial and military-grade system integration.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage Range | 1.5 V to 5.5 V - supports mixed-voltage system interfacing and battery-backed operation down to 1.5 V logic levels |
| Max Propagation Delay (VCC = 5 V) | 11 ns - enables use in sub-100 MHz address decoding paths without timing closure issues |
| Output Drive Current | ±24 mA - drives 15 F-type loads directly; eliminates need for external buffer stages in medium-fanout systems |
| ESD Rating (HBM) | ±2000 V - exceeds MIL-STD-883 requirement; suitable for assembly environments with moderate ESD controls |
| Operating Temperature | –55°C to +125°C - qualified for extended industrial and defense applications without derating |
| Power Dissipation Capacitance | 110 pF - determines dynamic power consumption at high toggle rates; critical for thermal budgeting in dense PCB layouts |
| Input Clamp Current | ±20 mA - defines safe current limit during overvoltage transients; informs external protection design |
Pinout & Package
CD74AC138ME4 uses a 16-pin plastic dual in-line package (PDIP-N), body size 19.3 mm × 6.35 mm, with through-hole mounting and industry-standard pin spacing (2.54 mm). Thermal performance is characterized by RθJA = 67°C/W.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A (1) | Address Input A | LSB of 3-bit binary select code; determines Y0–Y7 output activation in conjunction with B and C |
| B (2) | Address Input B | Middle bit of 3-bit select code; combined with A and C, fully decodes one of eight outputs |
| C (3) | Address Input C | MSB of 3-bit select code; required for full 3-to-8 decoding functionality |
| G2A (4) | Strobe Input 2A (active low) | First enable input; must be low with G2B and G1 high for decoder operation |
| G2B (5) | Strobe Input 2B (active low) | Second enable input; complements G2A in 3-input enable logic |
| G1 (6) | Strobe Input (active high) | Primary enable; high level activates decoding when G2A/G2B are low |
| Y7 (7) | Output 7 | Active-high decoded output corresponding to CBA = 111; driven low when selected |
| GND (8) | Ground Reference | Return path for all internal logic and output currents; requires low-impedance PCB connection |
| Y6 (9) | Output 6 | Active-high decoded output for CBA = 110; sinks or sources up to 24 mA |
| Y5 (10) | Output 5 | Active-high decoded output for CBA = 101; electrically identical to Y0–Y7 |
| Y4 (11) | Output 4 | Active-high decoded output for CBA = 100; shares same timing and drive specs as other Yx pins |
| Y3 (12) | Output 3 | Active-high decoded output for CBA = 011; no internal pull-up/pull-down; high-Z when disabled |
| Y2 (13) | Output 2 | Active-high decoded output for CBA = 010; compatible with TTL and CMOS load thresholds |
| Y1 (14) | Output 1 | Active-high decoded output for CBA = 001; transitions within 11 ns at 5 V supply |
| Y0 (15) | Output 0 | Active-high decoded output for CBA = 000; lowest-order output; matches timing spec of Y7 |
| VCC (16) | Positive Supply | Primary power rail; requires local 0.1 µF bypass capacitor per TI layout guidelines |
Key Features
| Feature | Design Value |
|---|---|
| Three Enable Inputs (G1, G2A, G2B) | Enables hierarchical decoding trees without external logic; allows daisy-chaining multiple CD74AC138ME4 devices for 4-to-16 or larger decoding |
| ±24 mA Output Drive | Directly interfaces with 74F/74AS logic families and small-signal MOSFET gates; avoids intermediate drivers in I/O expansion modules |
| SCR-Latchup Resistant Process | Guarantees immunity to latchup under transient overvoltage or hot-swap conditions in backplane and modular systems |
| 1.5 V to 5.5 V Wide Supply Range | Supports direct interface with 1.8 V, 3.3 V, and 5 V subsystems without level shifters in mixed-voltage boards |
| High-Speed Memory Decoding Focus | Optimized propagation delay and fanout minimize address decode skew in SRAM/ROM access paths and FPGA configuration buses |
Applications
| Memory Address Decoding | Industrial PLC I/O Expansion |
|---|---|
Use Scenario: Selecting one of eight memory banks in a microcontroller-based data logger with external SRAM and flash storage. IC Role / Device Role / Timing Role: CD74AC138ME4 acts as the primary address decoder, translating 3-bit bank select lines into individual chip-enable signals for parallel memory devices. Use Value: 11 ns propagation delay ensures memory access timing meets 25 MHz bus requirements without wait states; ±24 mA drive sustains signal integrity across 10 cm PCB traces. | Use Scenario: Expanding digital input capacity in an Allen-Bradley CompactLogix controller using discrete sensor inputs. IC Role / Device Role / Timing Role: CD74AC138ME4 routes 3-bit configuration codes from the main CPU to eight isolated input channel enable lines on an optocoupled I/O daughterboard. Use Value: –55°C to +125°C operating range matches PLC environmental specs; three enable inputs simplify firmware-controlled bank switching during runtime reconfiguration. |
| Legacy System Bus Interface | Test Equipment Signal Routing |
Use Scenario: Adapting a vintage Z80-based computer design to modern peripherals via ISA-compatible expansion slots. IC Role / Device Role / Timing Role: CD74AC138ME4 decodes upper address bits (A13–A15) to generate device-select signals for UART, PIO, and timer ICs on the bus. Use Value: TTL-compatible input thresholds and 5 V operation ensure seamless integration with 74LS logic; PDIP package allows hand-soldering on through-hole prototype boards. | Use Scenario: Configuring signal paths in a modular automated test system where one controller manages eight independent measurement channels. IC Role / Device Role / Timing Role: CD74AC138ME4 serves as a static routing switch, enabling one of eight analog multiplexer control lines based on FPGA-generated select bits. Use Value: Balanced tPLH/tPHL minimizes channel switching jitter; ±2000 V HBM rating protects against ESD events during probe contact and fixture handling. |
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 |
|---|---|---|---|
| SN74AC138N | Same AC logic family, identical pinout and electrical specs; manufactured by TI with identical -55°C to +125°C rating | No functional difference; SN74AC138N is the contemporary catalog-numbered variant with identical PDIP packaging and marking | Select SN74AC138N for new designs requiring TI's current production part number and full lifecycle support |
| 74HC138N | Higher propagation delay (24 ns max at 4.5 V), lower drive (±4 mA), narrower supply range (2 V–6 V), and no guaranteed –55°C operation | Suitable only for commercial-temperature consumer or lab equipment; not recommended for industrial or extended-temp deployments | Choose 74HC138N only if cost is primary concern and temperature range is limited to 0°C–70°C with relaxed timing budgets |
Compared with SN74AC138N, CD74AC138ME4 offers identical performance but reflects legacy TI military/catalog cross-reference nomenclature; versus 74HC138N, it delivers 2.2× faster switching, 6× higher drive strength, and guaranteed operation down to –55°C - making it essential for ruggedized embedded systems.
Availability
CD74AC138ME4 is available at Aetrix Electronics and suitable for industrial PLCs, legacy bus adapters, test equipment signal routing, and high-reliability memory decoding requiring stable component supply across extended temperature ranges.
Supply support for CD74AC138ME4 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 families.
The CD74AC138ME4 belongs to TI's Advanced CMOS (AC) logic series, engineered for high-speed memory decoding and data-routing applications demanding low power, wide voltage operation, and robust latchup immunity.
FAQ
What is the maximum propagation delay of CD74AC138ME4 at 5 V supply?
The maximum propagation delay of CD74AC138ME4 is 11 ns for address inputs (A/B/C) to any output (Y0–Y7) and 10 ns for enable inputs (G1, G2A/G2B) to any output, measured at VCC = 5 V ± 0.5 V, CL = 50 pF, and TA = –55°C to +125°C. These values are specified in Section 4.8 of the official TI datasheet SCHS328C.
Does CD74AC138ME4 have Schmitt-trigger inputs?
No, CD74AC138ME4 does not feature Schmitt-trigger inputs. The device uses standard CMOS inputs with defined VIH/VIL thresholds per Section 4.3 of the datasheet. Schmitt-trigger behavior is explicitly attributed to other members of the CDx4AC138 family in Section 6.1, but not to CD74AC138ME4 - confirmed by absence in pin function table and logic diagram.
What is the correct pin 1 orientation for CD74AC138ME4 in PDIP package?
For CD74AC138ME4 in the 16-pin PDIP (N) package, pin 1 is located at the top-left corner when the notch or dot marker on the package body is oriented upward. This matches JEDEC MS-001 standard for 16-pin DIP devices and is verified in Figure 3-1 of the TI datasheet SCHS328C.
Can CD74AC138ME4 operate at 1.8 V supply voltage?
Yes, CD74AC138ME4 is fully specified to operate at 1.8 V supply voltage, as its recommended operating range is 1.5 V to 5.5 V. At 1.8 V, VIH = 1.35 V min and VIL = 0.45 V max per Section 4.3, ensuring reliable logic-level compatibility with 1.8 V microcontrollers and FPGAs without level translation.
Is thermal pad soldering required for CD74AC138ME4?
No, thermal pad soldering is not required for CD74AC138ME4 because it uses a PDIP (N) package, which has no exposed thermal pad. The thermal pad reference in the datasheet applies exclusively to the WQFN (BQB) variant (e.g., CD74AC138BQBR); PDIP packages rely on lead-frame conduction and PCB copper area for thermal management.
CD74AC138ME4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74AC
- Package/Case:
- 16-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tube
- Product Status:
- Obsolete
- Type:
- Decoder/Demultiplexer
- Circuit:
- 1 x 3:8
- Independent Circuits:
- 1
- Current - Output High, Low:
- 24mA, 24mA
- Voltage Supply Source:
- Single Supply
- Voltage - Supply:
- 1.5V ~ 5.5V
- Operating Temperature:
- -55°C ~ 125°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SOIC
CD74AC138ME4 FAQ
1.How can I place an order for CD74AC138ME4 through Aetrix?
Please submit a Request for Quotation (RFQ) for CD74AC138ME4 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 CD74AC138ME4 reliable?
The price and inventory of CD74AC138ME4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for CD74AC138ME4 is usually 5 days.
3.What payment methods are accepted for CD74AC138ME4?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for CD74AC138ME4 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for CD74AC138ME4?
CD74AC138ME4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your CD74AC138ME4 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 CD74AC138ME4?
For technical support, including CD74AC138ME4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your CD74AC138ME4 requirements.
6.How does Aetrix verify that CD74AC138ME4 is sourced from the original manufacturer or authorized distributors?
All CD74AC138ME4 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 CD74AC138ME4 meets industry standards.
7.What is the process for return or replacement of CD74AC138ME4?
All CD74AC138ME4 units undergo pre-shipment inspection (PSI). If there is an issue with CD74AC138ME4, 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 CD74AC138ME4 part is unused and in its original packaging.
Return procedure for CD74AC138ME4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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