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Texas Instruments SN74HC138DRE4
- Part No.:
- SN74HC138DRE4
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
SN74HC138DRE4.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,143
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Product details
Overview
SN74HC138DRE4 from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in SOIC-16 package, operating across 2 V–6 V supply, delivering 15 ns typical propagation delay at 5 V, ±4 mA output drive, and active-low outputs with three enable inputs (two low, one high) for cascading. It serves as a memory address decoder in industrial control backplanes.
For engineers reviewing the SN74HC138DRE4 datasheet, SN74HC138DRE4 pinout, SN74HC138DRE4 application, or SN74HC138DRE4 equivalent, key selection criteria include its wide VCC range, low ICC (80 µA max), LSTTL-load compatibility, and precise enable-input logic sequencing for hierarchical decoding systems.
Technical Context
The SN74HC138DRE4 implements combinational logic decoding using CMOS technology, where binary inputs A/B/C select exactly one of eight active-low outputs (Y0–Y7) only when G1 = HIGH and both G2A/G2B = LOW. Its enable architecture allows direct cascading of multiple units without external inverters - e.g., two devices form a 24-line decoder, three with one inverter yield 32-line decoding.
Propagation delay is supply-voltage dependent: 15 ns (typ) at VCC = 6 V, 38 ns (max) over full temperature range (–40°C to +85°C), with input transition times specified down to 400 ns at 6 V. Output drive capability supports up to 10 LSTTL loads while maintaining VOL ≤ 0.33 V at IOL = 4 mA and VCC = 4.5 V.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 2 V to 6 V - enables interoperability with 3.3 V and 5 V logic families without level shifters. |
| tpd (typ) | 15 ns at VCC = 6 V - ensures minimal added latency in high-speed memory address decoding paths. |
| Output Drive | ±4 mA at VCC = 4.5 V - sufficient to directly sink/source standard LSTTL inputs without buffering. |
| ICC (max) | 80 µA at VCC = 6 V - supports low-static-power system design in battery-backed or energy-sensitive applications. |
| Input Current | ±1 µA max - eliminates need for pull-up/down resistors on unused enable or select lines in high-impedance states. |
| Enable Logic | G1 (active-HIGH), G2A/G2B (active-LOW) - simplifies hierarchical enable tree design with mixed-polarity control signals. |
| Operating Temp | –40°C to +85°C - qualified for industrial-grade embedded systems including factory automation controllers. |
Pinout & Package
SN74HC138DRE4 uses a 16-pin SOIC (D) package measuring 9.90 mm × 3.90 mm with standard 1.27 mm pitch. Pin numbering follows JEDEC MS-012, compatible with automated placement and reflow processes.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (A) | Select input A (LSB) | Binary address bit 0; determines least-significant output selection when enables are asserted. |
| 2 (B) | Select input B | Binary address bit 1; combines with A/C to uniquely select one of eight outputs. |
| 3 (C) | Select input C (MSB) | Binary address bit 2; completes 3-bit decode word for full 8-output mapping. |
| 4 (G2A) | Active-low enable A | Primary disable path; pulling HIGH forces all outputs HIGH regardless of A/B/C state. |
| 5 (G2B) | Active-low enable B | Secondary disable input; used with G2A for AND-gated enable logic in multi-device systems. |
| 6 (G1) | Active-high enable | Master enable; must be HIGH for any output to activate - enables global decode gating. |
| 7 (Y7) | Output 7 (MSB) | Active-low decoded output corresponding to A=1,B=1,C=1; sinks current when selected. |
| 8 (GND) | Ground reference | Return path for all internal logic and output currents; requires low-impedance PCB plane connection. |
| 15 (Y0) | Output 0 (LSB) | Active-low decoded output for A=0,B=0,C=0; used for lowest-address peripheral selection. |
| 16 (VCC) | Supply voltage | Power rail for CMOS logic core; requires local 0.1 µF ceramic bypass capacitor per device. |
Key Features
| Feature | Design Value |
|---|---|
| Three enable inputs | Enables hierarchical decoding: two active-low (G2A/G2B) and one active-high (G1) allow flexible cascade control without external gates. |
| Active-low outputs | Y0–Y7 assert LOW when selected - matches common cathode LED matrix and N-channel MOSFET gate-drive requirements. |
| Low power consumption | 80 µA max ICC at 6 V - reduces thermal load and extends battery life in portable instrumentation interfaces. |
| High noise immunity | VIH ≥ 3.15 V and VIL ≤ 1.35 V at VCC = 4.5 V - provides >1.3 V noise margin against EMI in industrial motor-control environments. |
| LSTTL-compatible drive | Sinks 4 mA at VOL ≤ 0.33 V - directly interfaces legacy TTL peripherals without level-shifting buffers. |
Applications
| LED Matrix Column Driver | Industrial Memory Address Decoder |
|---|---|
|
Use Scenario: Driving columns of an 8×8 monochrome LED display in multiplexed scanning mode. IC Role / Device Role / Timing Role: Low-side column selector that activates exactly one Yx output per scan cycle to ground the selected column line. Use Value: Eliminates need for discrete transistors per column; leverages active-low outputs and enable-controlled blanking for flicker-free display updates. |
Use Scenario: Decoding 3-bit address segments in programmable logic controller (PLC) I/O expansion modules. IC Role / Device Role / Timing Role: Address-space partitioner routing CPU read/write cycles to specific peripheral registers or memory-mapped sensors. Use Value: Reduces FPGA or microcontroller GPIO usage by offloading address decoding; supports hot-swap detection via G1 gating. |
| Server Backplane Select Logic | White Goods Control Panel Interface |
|
Use Scenario: Enabling one of eight PCIe slot power controllers or fan-speed regulators in modular server chassis. IC Role / Device Role / Timing Role: Cascaded enable distributor using G2A/G2B to isolate fault domains while G1 synchronizes with system reset. Use Value: Enables selective power sequencing and thermal throttling without software intervention or additional logic ICs. |
Use Scenario: Scanning keypad rows and activating indicator LEDs on refrigerator or oven control panels. IC Role / Device Role / Timing Role: Dual-role demultiplexer: selects keypad scan lines and drives LED status indicators simultaneously. Use Value: Integrates two functions into single SOIC-16 footprint, reducing BOM count and PCB area in cost-sensitive consumer appliances. |
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 |
|---|---|---|---|
| 74HC238PW | Identical logic function and pinout; TSSOP-16 package (5.0 mm × 4.4 mm) vs SOIC-16 (9.9 mm × 3.9 mm). | Preferred for space-constrained designs requiring finer pitch and lower profile; same electrical specs and temp range. | Choose 74HC238PW when board real estate is limited and reflow compatibility with fine-pitch components is confirmed. |
| SN74LS138N | Bipolar TTL implementation: higher ICC (19 mA typ), narrower VCC (4.75–5.25 V), slower tpd (22 ns min), and no 2–6 V flexibility. | Legacy replacement only; incompatible with mixed-voltage systems or low-power designs due to static current and voltage constraints. | Use SN74LS138N solely for drop-in replacement in existing 5 V TTL designs where power budget and voltage tolerance are not limiting. |
Compared with SN74HC138DRE4, 74HC238PW offers identical functionality in a smaller footprint but requires tighter layout tolerances, while SN74LS138N trades power efficiency and voltage flexibility for legacy TTL compatibility - making SN74HC138DRE4 optimal for modern industrial and mixed-supply systems.
Availability
SN74HC138DRE4 is available at Aetrix Electronics and suitable for industrial control panels, LED display subsystems, and server backplane management requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for SN74HC138DRE4 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 industrial, automotive, and communications markets.
SN74HC138DRE4 belongs to TI's HC logic family, designed for high-speed, low-power digital interfacing in memory systems, data routing, and peripheral selection - balancing speed, noise immunity, and power efficiency for industrial-grade reliability.
FAQ
What is the maximum supply voltage rating for SN74HC138DRE4?
The absolute maximum supply voltage for SN74HC138DRE4 is 7 V, but the recommended operating range is 2 V to 6 V per TI's SCLS107G datasheet. Operating above 6 V risks exceeding absolute maximum ratings and may cause permanent damage or accelerated parametric drift. Always maintain VCC within 2–6 V for reliable operation across –40°C to +85°C.
Does SN74HC138DRE4 support cascading with other decoders?
Yes, SN74HC138DRE4 supports direct cascading using its three enable inputs: G1 (active-HIGH), G2A and G2B (both active-LOW). For example, two SN74HC138DRE4 devices can implement a 24-line decoder without external inverters, and three units with one inverter achieve 32-line decoding - enabling scalable address expansion in memory or I/O subsystems.
What is the output behavior of SN74HC138DRE4 when all enable inputs are inactive?
When any enable input is inactive - i.e., G1 = LOW, or G2A = HIGH, or G2B = HIGH - all eight outputs (Y0–Y7) go HIGH regardless of A/B/C input states. This high-impedance-like behavior (outputs actively driven HIGH) ensures safe default states during power-up, reset, or fault conditions, preventing unintended peripheral activation.
Can SN74HC138DRE4 drive standard TTL loads directly?
Yes, SN74HC138DRE4 can drive up to 10 LSTTL loads per output, verified by its ±4 mA output drive specification at VCC = 4.5 V and VOL ≤ 0.33 V under IOL = 4 mA. This meets LS-TTL input current requirements (IIL ≤ 0.4 mA) with margin, eliminating need for buffer stages in most industrial interface applications.
Is SN74HC138DRE4 RoHS compliant and lead-free?
Yes, SN74HC138DRE4 is RoHS compliant with lead finish/NiPdAu (NIPDAU) plating and MSL Level-1 rating (260°C peak reflow, unlimited floor life). Per TI's PACKAGE OPTION ADDENDUM, it carries "Yes" in the RoHS column and is qualified for lead-free assembly processes without special handling requirements.
SN74HC138DRE4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74HC
- Package/Case:
- 16-SOIC (0.154", 3.90mm 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:
- 5.2mA, 5.2mA
- Voltage Supply Source:
- Single Supply
- Voltage - Supply:
- 2V ~ 6V
- Operating Temperature:
- -40°C ~ 85°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SOIC
SN74HC138DRE4 FAQ
1.How can I place an order for SN74HC138DRE4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74HC138DRE4 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 SN74HC138DRE4 reliable?
The price and inventory of SN74HC138DRE4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74HC138DRE4 is usually 5 days.
3.What payment methods are accepted for SN74HC138DRE4?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74HC138DRE4 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74HC138DRE4?
SN74HC138DRE4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74HC138DRE4 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 SN74HC138DRE4?
For technical support, including SN74HC138DRE4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74HC138DRE4 requirements.
6.How does Aetrix verify that SN74HC138DRE4 is sourced from the original manufacturer or authorized distributors?
All SN74HC138DRE4 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 SN74HC138DRE4 meets industry standards.
7.What is the process for return or replacement of SN74HC138DRE4?
All SN74HC138DRE4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74HC138DRE4, 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 SN74HC138DRE4 part is unused and in its original packaging.
Return procedure for SN74HC138DRE4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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