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Texas Instruments SN74HCT138PWRE4
- Part No.:
- SN74HCT138PWRE4
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-TSSOP (0.173", 4.40mm Width)
- Datasheet:
-
SN74HCT138PWRE4.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:4,448
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Product details
Overview
SN74HCT138PWRE4 from Texas Instruments is a 3-line to 8-line decoder/demultiplexer IC operating at 4.5 V–5.5 V, with 17 ns typical propagation delay (VCC = 5.5 V), ±4-mA output drive, and TTL-compatible inputs. It serves as a high-speed memory address decoder or data routing switch in embedded control and digital logic systems.
For engineers reviewing the SN74HCT138PWRE4 datasheet, SN74HCT138PWRE4 pinout, SN74HCT138PWRE4 application, or SN74HCT138PWRE4 equivalent, key selection criteria include enable-input architecture (two active-low + one active-high), LSTTL load drive capability (up to 10 loads), low ICC (80 µA max), input voltage compatibility, and TSSOP-16 package thermal performance (RθJA = 108 °C/W).
Technical Context
The SN74HCT138PWRE4 implements combinational logic decoding using three binary select inputs (A, B, C) and three enable terminals (G1, G2A, G2B) - two active-low and one active-high - enabling cascading without external inverters. Its function table defines eight mutually exclusive active-low outputs (Y0–Y7), each asserted only when all enables are satisfied and the select code matches.
Designed for memory-decoding applications, it minimizes system-level delay by ensuring tpd (17–34 ns, depending on VCC and condition) remains below typical fast-memory access times. The device uses HCMOS-compatible circuitry with TTL-voltage thresholds, allowing direct interfacing with legacy TTL logic while maintaining CMOS power efficiency.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage | 4.5 V to 5.5 V - ensures compatibility with standard 5-V TTL and mixed-signal systems. |
| Propagation Delay (tpd) | 17 ns typ @ VCC = 5.5 V - enables use in sub-20-ns timing-critical address decoding paths. |
| Output Drive | ±4 mA @ 5 V - supports direct fanout to 10 LSTTL loads without buffering. |
| Supply Current (ICC) | 80 µA max - enables low-static-power operation in battery-backed or energy-sensitive logic subsystems. |
| Input Compatibility | TTL-voltage compatible (VIH = 2 V, VIL = 0.8 V) - allows seamless integration with legacy 74LS/74F logic families. |
| Operating Temperature | –40 °C to +85 °C - qualified for industrial-grade embedded controller and peripheral interface applications. |
| Power Dissipation Cap. | 85 pF typ - quantifies dynamic switching power consumption under no-load conditions. |
Pinout & Package
TSSOP-16 package (5.00 mm × 4.40 mm, 1.2 mm max height), RoHS-compliant, moisture sensitivity level 1, lead finish NiPdAu/Sn.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (G2A) | Active-low enable input | Must be LOW to activate decoder; used for hierarchical enable chaining with other '138 devices. |
| 2 (G2B) | Active-low enable input | Second independent enable; both G2A and G2B must be LOW for decode operation. |
| 3 (G1) | Active-high enable input | Must be HIGH to enable outputs; simplifies cascading with minimal external logic. |
| 4 (C) | MSB binary select input | Most significant bit of 3-bit address; determines Y4–Y7 vs. Y0–Y3 activation group. |
| 5 (B) | Mid-bit binary select input | Controls quadrant selection within enabled group (e.g., Y0/Y1 vs. Y2/Y3). |
| 6 (A) | LSB binary select input | Least significant bit; selects individual output line (e.g., A=0/B=0/C=0 → Y0 active). |
| 7 (Y0) | Active-low decoded output | Asserted LOW only when G1=H, G2A=L, G2B=L, and CBA=000 - used for chip-select or strobe generation. |
| 8 (GND) | Ground reference | Primary return path for all internal logic and output currents; requires low-impedance PCB connection. |
| 9 (Y1) | Active-low decoded output | Asserted LOW only when CBA=001 - provides discrete channel selection in demultiplexing mode. |
| 10 (Y2) | Active-low decoded output | Asserted LOW only when CBA=010 - supports 1-of-8 signal routing in bus arbitration or peripheral enable trees. |
| 11 (Y3) | Active-low decoded output | Asserted LOW only when CBA=011 - enables compact implementation of 4-bit I/O port expansion. |
| 12 (Y4) | Active-low decoded output | Asserted LOW only when CBA=100 - used in memory bank selection where MSB drives higher-address regions. |
| 13 (Y5) | Active-low decoded output | Asserted LOW only when CBA=101 - supports interleaved memory mapping schemes. |
| 14 (Y6) | Active-low decoded output | Asserted LOW only when CBA=110 - facilitates multi-peripheral interrupt prioritization via wired-OR configuration. |
| 15 (Y7) | Active-low decoded output | Asserted LOW only when CBA=111 - final output for full 3-bit decode space; commonly tied to system reset or watchdog enable. |
| 16 (VCC) | Positive supply rail | 5-V nominal power input; requires local 0.1-µF ceramic bypass capacitor placed adjacent to pin. |
Key Features
| Feature | Design Value |
|---|---|
| Three enable inputs (G1, G2A, G2B) | Enables 24-line decoding without external inverters and 32-line with only one inverter - reduces board area and component count in multi-chip select systems. |
| Active-low outputs (Y0–Y7) | Supports direct wired-OR interrupt aggregation and negative-logic chip-select architectures common in microcontroller peripheral interfaces. |
| TTL-compatible input thresholds | Eliminates level-shifting requirements when interfacing with 74LS, 74F, or microcontroller GPIOs operating at 5 V. |
| Low ICC (80 µA max) | Reduces quiescent power in always-on logic sections such as boot ROM decoders or real-time clock domain selectors. |
| 17 ns tpd @ 5.5 V | Meets timing budgets for ≤50-MHz address bus systems where decoder delay contributes directly to memory access latency. |
Applications
| Memory Address Decoding | Peripheral I/O Expansion |
|---|---|
Use Scenario: Selecting one of eight SRAM or Flash memory chips in a microcontroller-based embedded system with limited address lines. IC Role / Device Role / Timing Role: 3-to-8 address decoder generating individual chip-select (CS#) signals synchronized to address bus transitions. Use Value: Enables full utilization of 16-bit address space across multiple memory banks while keeping total decode delay under 34 ns - preserving system timing margins. | Use Scenario: Expanding GPIO capability of an MCU by enabling/disabling up to eight peripheral ICs (e.g., ADCs, DACs, sensors) via shared SPI/I²C bus. IC Role / Device Role / Timing Role: Demultiplexer routing control signals (CS#, RESET#, INT#) to selected peripherals based on 3-bit command register value. Use Value: Reduces firmware complexity by eliminating manual GPIO bit-banging; supports hot-plug detection through dedicated Yx-driven status lines. |
| Interrupt Prioritization Tree | Bus Arbitration Logic |
Use Scenario: Aggregating interrupt requests from eight sensor nodes into a single IRQ line for an ARM Cortex-M4 core. IC Role / Device Role / Timing Role: Priority encoder front-end where Y0–Y7 feed a priority encoder IC or are wire-OR'd to MCU IRQ pin with pull-up. Use Value: Provides deterministic interrupt response order (Y0 highest priority) without software polling - cuts worst-case latency by >60% versus daisy-chained polling. | Use Scenario: Managing access to a shared parallel data bus among four DMA controllers and four peripheral modules. IC Role / Device Role / Timing Role: Bus grant decoder asserting one of eight BUSREQ# lines based on master ID bits and arbitration state machine output. Use Value: Ensures glitch-free bus handoff with <20 ns setup/hold margin relative to clock edge - prevents data corruption during high-throughput transfers. |
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 |
|---|---|---|---|
| SN74HC138N | Higher VCC range (2–6 V), slower tpd (29 ns typ @ 6 V), lower drive (±4 mA), non-TTL input thresholds (VIH = 3.15 V min). | Suitable for mixed-voltage systems but incompatible with legacy 5-V TTL logic without level translation. | Select SN74HC138N only if operating below 4.5 V or requiring wider supply flexibility; avoid when interfacing with 74LS/74F families. |
| 74ACT138SCX | Faster tpd (6.5 ns typ @ 5 V), higher drive (±24 mA), same TTL-compatible inputs, SOIC-16 package. | Better suited for ultra-high-speed bus steering but consumes more power (ICC = 4 µA typ) and lacks industrial temp range. | Choose 74ACT138SCX only for sub-10-ns timing-critical designs where SN74HCT138PWRE4's 17 ns is insufficient. |
Compared with SN74HC138N and 74ACT138SCX, the SN74HCT138PWRE4 uniquely balances TTL compatibility, industrial temperature range, low static current, and sub-20-ns speed - making it optimal for cost-sensitive, reliability-critical 5-V embedded systems where interoperability with legacy logic is mandatory.
Availability
SN74HCT138PWRE4 is available at Aetrix Electronics and suitable for memory address decoding, peripheral I/O expansion, interrupt prioritization, and bus arbitration applications requiring stable component supply and long-term industrial lifecycle support.
Supply support for SN74HCT138PWRE4 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 90 years of innovation in industrial, automotive, and communications markets.
The SN74HCT138PWRE4 belongs to TI's 74HCT logic family, engineered specifically for high-speed memory decoding and data-routing systems where TTL compatibility, low power, and precise propagation delay are critical design requirements.
FAQ
What is the maximum propagation delay of the SN74HCT138PWRE4 under recommended operating conditions?
The maximum propagation delay (tpd) of the SN74HCT138PWRE4 is 49 ns when VCC = 5.5 V and TA = 25°C, measured from any enable or select input to any Y output under CL = 50 pF. At VCC = 4.5 V, the max tpd increases to 54 ns. These values are specified in the Switching Characteristics table of the official TI datasheet SCLS171F.
Can the SN74HCT138PWRE4 drive standard TTL loads directly?
Yes, the SN74HCT138PWRE4 can drive up to 10 LSTTL loads directly. Its output drive capability is ±4 mA at VCC = 5 V, meeting the LSTTL input current requirements (IIH = 20 µA, IIL = –0.4 mA). This eliminates the need for buffer stages in most 5-V logic systems, as confirmed in the Features and Electrical Characteristics sections of the SN74HCT138PWRE4 datasheet.
What are the valid logic states for the enable inputs of the SN74HCT138PWRE4?
The SN74HCT138PWRE4 has three enable inputs: G1 (active-high), G2A (active-low), and G2B (active-low). All outputs are disabled (high-impedance inactive state) unless G1 = HIGH, G2A = LOW, and G2B = LOW simultaneously. This triple-enable structure is explicitly defined in the Function Table (Table 7-1) of the SN74HCT138PWRE4 datasheet and enables flexible cascading configurations.
Is the SN74HCT138PWRE4 RoHS compliant and what is its moisture sensitivity level?
Yes, the SN74HCT138PWRE4 is RoHS compliant with NiPdAu/Sn lead finish and carries a moisture sensitivity level (MSL) rating of Level-1 at 260°C peak reflow. This information is documented in TI's Package Option Addendum for SN74HCT138PWRE4, confirming suitability for standard surface-mount assembly processes without baking requirements.
How does the SN74HCT138PWRE4 differ from the SN74HCT138PWR variant?
The SN74HCT138PWRE4 and SN74HCT138PWR share identical electrical specifications, pinout, and TSSOP-16 package, but differ in marking and qualification: SN74HCT138PWRE4 features "HT138" part marking and is rated for industrial temperature (–40°C to +85°C), while SN74HCT138PWR uses the same marking and is also industrial-grade. Both are active production parts per TI's packaging addendum, with E4 suffix indicating green/RoHS-compliant packaging.
SN74HCT138PWRE4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74HCT
- Package/Case:
- 16-TSSOP (0.173", 4.40mm 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:
- 4mA, 4mA
- 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-TSSOP
SN74HCT138PWRE4 FAQ
1.How can I place an order for SN74HCT138PWRE4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74HCT138PWRE4 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 SN74HCT138PWRE4 reliable?
The price and inventory of SN74HCT138PWRE4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74HCT138PWRE4 is usually 5 days.
3.What payment methods are accepted for SN74HCT138PWRE4?
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SN74HCT138PWRE4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74HCT138PWRE4 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 SN74HCT138PWRE4?
For technical support, including SN74HCT138PWRE4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74HCT138PWRE4 requirements.
6.How does Aetrix verify that SN74HCT138PWRE4 is sourced from the original manufacturer or authorized distributors?
All SN74HCT138PWRE4 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 SN74HCT138PWRE4 meets industry standards.
7.What is the process for return or replacement of SN74HCT138PWRE4?
All SN74HCT138PWRE4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74HCT138PWRE4, 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 SN74HCT138PWRE4 part is unused and in its original packaging.
Return procedure for SN74HCT138PWRE4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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