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Texas Instruments SN74HC138DBR
- Part No.:
- SN74HC138DBR
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SSOP (0.209", 5.30mm Width)
- Datasheet:
-
SN74HC138DBR.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16SSOP
- Quantity:
- Payment:
- Shipping:
Inventory:4,410
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Product details
Overview
SN74HC138DBR from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in SSOP-16 package, operating from 2 V to 6 V, with typical propagation delay of 15 ns at 6 V, ±4-mA output drive at 5 V, and active-low outputs enabling precise low-side LED column selection in multiplexed displays.
For engineers reviewing the SN74HC138DBR datasheet, SN74HC138DBR pinout, SN74HC138DBR application, or SN74HC138DBR equivalent, this device serves as a high-speed memory decoder and data-routing IC where low-power CMOS logic, cascading enable architecture, and TTL-load compatibility are critical selection criteria.
Technical Context
The SN74HC138DBR implements a binary-decoded 3-input (A, B, C) to 8-output (Y0–Y7) logic function with three enable inputs: one active-high (G1) and two active-low (G2A, G2B). All outputs are active-low and mutually exclusive - only one output asserts LOW per valid input combination when all enables are satisfied.
Its CMOS design ensures low static current (≤80 µA ICC), high noise immunity (VIH ≥3.15 V at VCC = 4.5 V), and robust fan-out capability (driving up to 10 LSTTL loads). The enable structure allows direct cascading of multiple units without external inverters for larger decoding trees.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage | 2 V to 6 V - supports mixed-voltage system interfacing and battery-powered operation down to 2 V logic levels. |
| Propagation Delay (tpd) | 15 ns typical at VCC = 6 V - enables use in high-speed memory address decoding where delay must be negligible versus memory access time. |
| Output Drive | ±4 mA at VCC = 5 V - sufficient to directly sink/source standard LSTTL inputs and drive LED columns without external buffers. |
| Input Current (II) | ≤1 µA max - minimizes loading on upstream logic and preserves signal integrity in large fan-out configurations. |
| Power Consumption (ICC) | 80 µA maximum - ensures ultra-low quiescent power in always-on control subsystems and portable equipment. |
| Operating Temperature | –40 °C to +85 °C - qualified for industrial-grade embedded applications including factory automation and building controls. |
Pinout & Package
SN74HC138DBR uses a 16-pin SSOP (Shrink Small Outline Package) with nominal body size 6.20 mm × 5.30 mm and 0.65-mm lead pitch. It is RoHS-compliant, moisture sensitivity level (MSL) 1, and rated for reflow up to 260 °C.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (A) | Select input A (LSB) | Binary address bit 0; determines least-significant output selection when enables are active. |
| 2 (B) | Select input B | Binary address bit 1; combines with A and C to uniquely select one of eight outputs. |
| 3 (C) | Select input C (MSB) | Binary address bit 2; completes 3-bit decode for full 8-output mapping. |
| 4 (G2A) | Active-low enable A | Global disable control; pulling HIGH forces all outputs HIGH regardless of A/B/C state. |
| 5 (G2B) | Active-low enable B | Second active-low enable; both G2A and G2B must be LOW for decode to proceed. |
| 6 (G1) | Active-high enable | Primary enable; must be HIGH along with G2A/G2B LOW to activate decoding function. |
| 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 | Logic and power return path; requires low-impedance connection to minimize switching noise. |
| 9 (Y6) | Output 6 | Active-low output for A=0, B=1, C=1; used in priority encoding or segmented display drivers. |
| 10 (Y5) | Output 5 | Active-low output for A=1, B=0, C=1; supports discrete channel selection in I/O expansion. |
| 11 (Y4) | Output 4 | Active-low output for A=0, B=0, C=1; commonly tied to interrupt lines or peripheral chip selects. |
| 12 (Y3) | Output 3 | Active-low output for A=1, B=1, C=0; used in memory bank selection and bus arbitration logic. |
| 13 (Y2) | Output 2 | Active-low output for A=0, B=1, C=0; interfaces directly with microcontroller GPIOs for peripheral enable. |
| 14 (Y1) | Output 1 | Active-low output for A=1, B=0, C=0; drives low-side switches or LED cathodes in scanning arrays. |
| 15 (Y0) | Output 0 (LSB) | Active-low output for A=0, B=0, C=0; default selection for reset or initialization sequences. |
| 16 (VCC) | Supply voltage | Positive supply rail; requires local 0.1-µF ceramic bypass capacitor placed adjacent to pin. |
Key Features
| Feature | Design Value |
|---|---|
| Three enable inputs (G1, G2A, G2B) | Enables hierarchical decoding: two SN74HC138DBR devices can form a 4-to-16 decoder without external inverters. |
| Active-low outputs (Y0–Y7) | Directly interfaces with N-channel MOSFETs or NPN transistors for low-side switching in LED matrix column drivers. |
| Wide supply range (2 V–6 V) | Permits interoperability across 3.3 V microcontrollers and 5 V legacy peripherals without level-shifting circuitry. |
| Low input current (≤1 µA) | Reduces loading on FPGA I/O banks or microcontroller pins driving multiple decoders in parallel. |
| High noise immunity (VIH ≥3.15 V @ 4.5 V) | Ensures reliable operation in electrically noisy industrial environments with marginal signal margins. |
Applications
| LED Matrix Display Control | Industrial I/O Expansion |
|---|---|
Use Scenario: Driving 8-column cathodes in an 8×8 monochrome LED matrix using row-scanning technique. IC Role / Device Role / Timing Role: Low-side column selector that sequentially activates one Y output per scan cycle while remaining outputs stay HIGH. Use Value: Eliminates need for discrete transistor arrays; single SN74HC138DBR replaces eight individual NPN switches with matched timing and reduced board area. |
Use Scenario: Expanding GPIO count of a PLC controller to manage 16 discrete sensors via two cascaded decoders. IC Role / Device Role / Timing Role: Address decoder translating 4-bit microcontroller port outputs into 16 independent enable signals. Use Value: Enables deterministic sensor polling with zero software overhead - hardware-selectable channels reduce CPU interrupt load. |
| Memory Address Decoding | Factory Automation Bus Arbitration |
Use Scenario: Selecting among eight SRAM chips in a 64-kB memory subsystem with fast access requirements. IC Role / Device Role / Timing Role: High-speed address decoder whose tpd (15 ns @ 6 V) stays below typical SRAM access time (≥35 ns). Use Value: Adds negligible system delay; eliminates wait states and maintains full memory bandwidth in real-time control loops. |
Use Scenario: Managing shared communication lines between HMI panel, motion controller, and safety module in a CNC machine. IC Role / Device Role / Timing Role: Priority encoder interface that routes CAN or RS-485 traffic to one of eight peripheral nodes based on address bits. Use Value: Provides deterministic, glitch-free bus access control without software arbitration delays or collision risk. |
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 pinout and logic function but includes latched inputs; requires separate latch-enable strobe. | Suitable for systems requiring synchronous input capture (e.g., sampled address buses), not direct combinatorial decode. | Choose 74HC238PW only if input latching is required; SN74HC138DBR remains optimal for pure address decoding. |
| SN74LV138ADBR | Lower VCC range (1.65 V–5.5 V); improved noise margin at 3.3 V; slightly higher tpd (19 ns @ 3.3 V). | Better suited for modern 3.3 V-only systems with tighter noise budgets; not recommended for 5 V or mixed-voltage designs. | Select SN74LV138ADBR for new 3.3 V ASIC/FPGA interfaces; retain SN74HC138DBR for backward compatibility with 5 V peripherals. |
Compared with 74HC238PW and SN74LV138ADBR, the SN74HC138DBR offers the broadest voltage flexibility (2–6 V), lowest propagation delay at 6 V, and simplest enable architecture - making it the preferred choice for general-purpose high-speed decoding in industrial and embedded systems.
Availability
SN74HC138DBR is available at Aetrix Electronics and suitable for industrial I/O expansion, LED matrix display control, memory address decoding, and factory automation bus arbitration requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for SN74HC138DBR 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 industrial and automotive components.
The SN74HC138DBR belongs to TI's HC (High-Speed CMOS) logic family, designed specifically for high-performance memory decoding and data-routing applications where low power, fast propagation, and robust noise immunity are essential.
FAQ
What is the maximum supply voltage rating for SN74HC138DBR?
The absolute maximum supply voltage for SN74HC138DBR is 7 V, but the recommended operating range is 2 V to 6 V per TI's SCLS107G datasheet. Operation above 6 V risks exceeding absolute maximum ratings and may cause irreversible damage. For reliable long-term performance, maintain VCC within 2–6 V, with 5 V being the most common implementation point for TTL-compatible systems.
Does SN74HC138DBR support cascading with other decoders?
Yes, SN74HC138DBR supports seamless cascading using its three enable inputs: G1 (active-high), G2A, and G2B (both active-low). By connecting outputs of one SN74HC138DBR to the enable pins of others, up to eight devices can be combined into a 6-to-64 decoder. No external inverters are needed due to the dual-active-low enable architecture, simplifying hierarchical address decoding in large memory or I/O systems.
Can SN74HC138DBR drive LEDs directly?
Yes, SN74HC138DBR can drive LEDs directly in low-side configuration: each active-low output (Y0–Y7) sinks up to 4 mA at 5 V, sufficient for indicator LEDs or low-current segments in multiplexed displays. For higher-current LEDs, pair with external N-channel MOSFETs or bipolar transistors. Always include current-limiting resistors - e.g., 330 Ω for ~10 mA at 5 V - to prevent exceeding output current limits.
What is the thermal resistance (RθJA) of SN74HC138DBR in its SSOP package?
The junction-to-ambient thermal resistance (RθJA) for SN74HC138DBR in the SSOP-16 (DB) package is 104.3 °C/W, as specified in Section 6.4 of the TI datasheet. This value assumes standard JEDEC 2-layer board conditions. For high-density PCB layouts or elevated ambient temperatures, derate power dissipation accordingly - maximum allowable power under continuous operation is approximately 48 mW at 85 °C ambient.
Is SN74HC138DBR compatible with 3.3 V microcontrollers?
Yes, SN74HC138DBR is fully compatible with 3.3 V microcontrollers: its VIH minimum is 2.0 V at VCC = 3.3 V (per Section 6.3), well within typical 3.3 V GPIO high-level output (≥2.4 V). Outputs swing rail-to-rail, providing clean 0 V / 3.3 V logic levels. No level shifters are required, making SN74HC138DBR ideal for interfacing ARM Cortex-M or RISC-V MCUs in mixed-voltage embedded systems.
SN74HC138DBR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74HC
- Package/Case:
- 16-SSOP (0.209", 5.30mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- 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-SSOP
SN74HC138DBR FAQ
1.How can I place an order for SN74HC138DBR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74HC138DBR 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 SN74HC138DBR reliable?
The price and inventory of SN74HC138DBR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74HC138DBR is usually 5 days.
3.What payment methods are accepted for SN74HC138DBR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74HC138DBR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74HC138DBR?
SN74HC138DBR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74HC138DBR 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 SN74HC138DBR?
For technical support, including SN74HC138DBR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74HC138DBR requirements.
6.How does Aetrix verify that SN74HC138DBR is sourced from the original manufacturer or authorized distributors?
All SN74HC138DBR 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 SN74HC138DBR meets industry standards.
7.What is the process for return or replacement of SN74HC138DBR?
All SN74HC138DBR units undergo pre-shipment inspection (PSI). If there is an issue with SN74HC138DBR, 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 SN74HC138DBR part is unused and in its original packaging.
Return procedure for SN74HC138DBR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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