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Texas Instruments SN74AHCT138PWE4
- Part No.:
- SN74AHCT138PWE4
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-TSSOP (0.173", 4.40mm Width)
- Datasheet:
-
SN74AHCT138PWE4.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:720
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Product details
Overview
SN74AHCT138PWE4 from Texas Instruments is a 3-line to 8-line decoder/demultiplexer IC designed for high-speed memory decoding and data-routing applications. It features three enable inputs (G1 active-high, G2A/G2B active-low), TTL-voltage-compatible inputs (VIH = 2 V, VIL = 0.8 V), and delivers propagation delays as low as 1 ns at 5 V with 15 pF load. It operates across 1.5–5.5 V supply and supports industrial temperature range (−40°C to +85°C), making it suitable for embedded control logic and address decoding in microcontroller-based systems.
For engineers reviewing the SN74AHCT138PWE4 datasheet, SN74AHCT138PWE4 pinout, SN74AHCT138PWE4 application, or SN74AHCT138PWE4 equivalent, key selection considerations include its 16-pin TSSOP package (PW), 8 active-low decoded outputs (Y0–Y7), enable-input cascading capability, and compatibility with legacy TTL logic levels in mixed-voltage digital systems.
Technical Context
The SN74AHCT138PWE4 implements positive-logic 3-to-8 decoding with three independent enable controls that allow hierarchical expansion-e.g., two devices can form a 24-line decoder without external inverters, while three support 32-line decoding with only one inverter. Its functional modes are fully defined by the truth table in Section 6.3, where output selection requires all enables asserted (G1 = H, G2A = L, G2B = L) and binary inputs A/B/C determining the single active-low output line.
Internally, it uses standard AHCT-series CMOS circuitry optimized for speed-power trade-offs: typical propagation delay is 7.6 ns (tPLH/tPHL) at 5 V/15 pF, with power dissipation capacitance of 14 pF and supply current under static conditions ≤40 mA. Input transition rate tolerance is specified at 20 ns/V, ensuring robust timing margin against slow-rising signals.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage Range | 1.5 V to 5.5 V - supports direct interface with 3.3 V and 5 V logic families without level shifters |
| Propagation Delay (tPLH/tPHL) | 1 ns (min) / 12 ns (max) at VCC = 5 V, CL = 15 pF - enables sub-100 MHz synchronous decoding in memory subsystems |
| Input Voltage Thresholds | VIH = 2 V, VIL = 0.8 V - ensures reliable recognition of standard TTL logic levels across voltage rails |
| Output Drive Strength | IOL = 8 mA / IOH = −8 mA at VO = 0.5 V / 3.8 V - sufficient to drive multiple 74AHCT inputs or small capacitive loads |
| ESD Robustness | ±2000 V HBM, ±1000 V CDM - meets JEDEC JESD22-A114 and JESD22-C101 for production handling safety |
| Operating Temperature | −40°C to +85°C - qualified for industrial-grade embedded applications including motor control and instrumentation |
| Power Dissipation Capacitance | 14 pF - enables accurate dynamic power estimation (P = Cpd × V² × f) in clocked systems |
Pinout & Package
TSSOP-16 (PW) package: 5.0 mm × 6.4 mm body size, 0.65 mm pitch, 1.2 mm max height, lead finish NiPdAu (SN), moisture sensitivity level 1 (260°C peak reflow).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A (1) | Binary select input A | LSB of 3-bit address; determines output Y0–Y7 mapping per function table |
| B (2) | Binary select input B | Middle bit of address; combined with A and C defines decoded output line |
| C (3) | Binary select input C | MSB of address; required for full 3-to-8 decoding resolution |
| G2A (4) | Active-low strobe input 2A | First enable control; must be low with G2B low and G1 high for decode operation |
| G2B (5) | Active-low strobe input 2B | Second enable control; used with G2A to reduce external gating in cascaded designs |
| G1 (6) | Active-high strobe input | Primary enable; high state permits decoding when both G2A and G2B are low |
| Y7 (7) | Active-low decoded output 7 | Asserted low when A=B=C=1 and all enables active; drives downstream logic or memory chip selects |
| GND (8) | Ground reference | Return path for all internal logic and output currents; requires low-inductance PCB connection |
| Y6 (9) | Active-low decoded output 6 | Asserted low when A=0, B=1, C=1; one of eight mutually exclusive outputs |
| Y5 (10) | Active-low decoded output 5 | Asserted low when A=1, B=0, C=1; supports discrete peripheral addressing |
| Y4 (11) | Active-low decoded output 4 | Asserted low when A=0, B=0, C=1; used in I/O port expansion schemes |
| Y3 (12) | Active-low decoded output 3 | Asserted low when A=1, B=1, C=0; enables selective activation of serial interface peripherals |
| Y2 (13) | Active-low decoded output 2 | Asserted low when A=0, B=1, C=0; commonly tied to interrupt controller inputs |
| Y1 (14) | Active-low decoded output 1 | Asserted low when A=1, B=0, C=0; provides dedicated enable for analog front-end modules |
| Y0 (15) | Active-low decoded output 0 | Asserted low when A=B=C=0; default output for boot-time configuration or reset circuits |
| VCC (16) | Positive supply | Primary power rail; requires local 0.1 µF ceramic bypass capacitor adjacent to pin |
Key Features
| Feature | Design Value |
|---|---|
| TTL-input compatibility | Accepts standard 5 V TTL logic thresholds (VIH = 2 V, VIL = 0.8 V) while operating from 1.5–5.5 V supply - eliminates need for external level translators |
| Three enable inputs | G1 (active-high), G2A/G2B (active-low) enable hierarchical decoding - allows 24-line expansion without inverters and 32-line with one inverter |
| High-speed propagation | Typical tPLH/tPHL = 7.6 ns at 5 V/15 pF - minimizes system decoding delay in high-performance memory interfaces |
| Latch-up immunity | Exceeds 250 mA per JESD17 - ensures robust operation in noisy industrial environments with transient coupling |
| Low dynamic power | Cpd = 14 pF - reduces switching power consumption in battery-powered or thermally constrained applications |
Applications
| Memory Address Decoding | Peripheral Select Logic |
|---|---|
Use Scenario: Selecting one of eight SRAM or Flash memory chips in a 16-bit microcontroller system using A15–A13 address lines. IC Role / Device Role / Timing Role: 3-to-8 decoder translating upper address bits into individual chip-select signals with <12 ns propagation delay. Use Value: Eliminates timing bottlenecks in memory access cycles; enables full utilization of CPU bus bandwidth without wait states. | Use Scenario: Enabling specific UART, SPI, or ADC peripherals on an FPGA carrier board based on command register values. IC Role / Device Role / Timing Role: Demultiplexer routing control bus signals to one of eight peripheral enable lines with simultaneous enable-input gating. Use Value: Reduces FPGA I/O count and simplifies firmware register mapping by offloading address decoding to dedicated hardware. |
| Industrial I/O Expansion | Legacy System Interface |
Use Scenario: Adding 8-channel digital output capability to a PLC mainboard via isolated optocoupler drivers. IC Role / Device Role / Timing Role: Decoder driving base inputs of eight NPN transistor switches, synchronized to microcontroller GPIO write strobes. Use Value: Provides deterministic, glitch-free output activation with no software overhead; supports real-time response within 15 ns. | Use Scenario: Interfacing modern 3.3 V microcontrollers to legacy 5 V TTL backplanes requiring strict VIH/VIL compliance. IC Role / Device Role / Timing Role: Level-tolerant address decoder accepting 3.3 V logic inputs while driving 5 V-tolerant outputs to legacy peripherals. Use Value: Enables drop-in replacement of obsolete 74LS138 without redesigning power or signal integrity paths. |
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 |
|---|---|---|---|
| SN74HCT138DR | Same pinout, identical logic function, but HCT family has wider VIH/VIL (2 V/0.8 V same), slightly higher ICC (max 40 mA vs 40 mA), and identical tPLH/tPHL specs | No functional difference; HCT version offers identical performance with broader commercial temp range (−40°C to +85°C same) | Select SN74HCT138DR if sourcing flexibility or dual-sourcing is required; electrically interchangeable in all SN74AHCT138PWE4 designs |
| 74LV138PW | Lower VCC range (1.0–5.5 V), higher speed (tPD = 5.5 ns typ), but VIH = 0.7×VCC (not fixed 2 V), limiting TTL compatibility | Not suitable for TTL-level input systems; requires ≥2.0 V input for guaranteed HIGH at 3.3 V supply, unlike SN74AHCT138PWE4's fixed 2 V threshold | Choose 74LV138PW only in pure 3.3 V or mixed 1.8/3.3 V systems where TTL compatibility is unnecessary and speed is critical |
Compared with SN74HCT138DR, SN74AHCT138PWE4 offers identical functionality and pinout but targets tighter propagation-delay consistency across voltage and temperature; versus 74LV138PW, it guarantees TTL-level input recognition at any supply voltage ≥1.5 V, enabling seamless integration into legacy 5 V designs without level-shifting overhead.
Availability
SN74AHCT138PWE4 is available at Aetrix Electronics and suitable for industrial control systems, embedded memory subsystems, and programmable logic peripheral interfaces requiring stable component supply and long-term manufacturability.
Supply support for SN74AHCT138PWE4 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 SN74AHCT138PWE4 belongs to TI's advanced high-speed CMOS logic family, engineered specifically for low-latency memory decoding and data routing in resource-constrained embedded systems where timing predictability and TTL interoperability are essential.
FAQ
What is the maximum recommended supply voltage for SN74AHCT138PWE4?
The absolute maximum supply voltage for SN74AHCT138PWE4 is 7 V, but the recommended operating range is 1.5 V to 5.5 V per TI's SCLS266O datasheet. Operating above 5.5 V risks exceeding electrical characteristics limits and may cause accelerated device degradation. For reliable long-term operation in industrial applications, maintain VCC within 5.0 V ±5%.
Does SN74AHCT138PWE4 support cascading for larger decoding schemes?
Yes, SN74AHCT138PWE4 supports cascading via its three enable inputs (G1, G2A, G2B). Two devices can implement a 24-line decoder without external inverters; three devices achieve 32-line decoding with only one external inverter. This architecture reduces gate count and propagation delay compared to discrete logic solutions.
Is SN74AHCT138PWE4 compatible with standard TTL input levels?
Yes, SN74AHCT138PWE4 features TTL-voltage-compatible inputs: VIH = 2 V (minimum) and VIL = 0.8 V (maximum) across the full 1.5–5.5 V supply range. This ensures reliable recognition of legacy 5 V TTL outputs without level shifters, distinguishing it from LV- or LVC-series decoders with ratio-based thresholds.
What is the thermal resistance (RθJA) of SN74AHCT138PWE4 in its TSSOP package?
The junction-to-ambient thermal resistance (RθJA) for SN74AHCT138PWE4 in the PW (TSSOP-16) package is 135.9°C/W, as specified in Section 4.4 of the datasheet. This value assumes standard JEDEC test board conditions; actual PCB layout with copper pour and thermal vias can improve thermal performance significantly.
Can unused inputs on SN74AHCT138PWE4 be left floating?
No, unused inputs on SN74AHCT138PWE4 must be tied to VCC or GND to prevent floating states that cause increased ICC, noise susceptibility, and potential logic malfunction. TI's SCBA004 application report explicitly recommends hard-wiring all unused inputs to defined logic levels - never leaving them unconnected.
SN74AHCT138PWE4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74AHCT
- Package/Case:
- 16-TSSOP (0.173", 4.40mm Width)
- Packaging:
- Bulk
- Product Status:
- Active
- Type:
- Decoder/Demultiplexer
- Circuit:
- 1 x 3:8
- Independent Circuits:
- 1
- Current - Output High, Low:
- 8mA, 8mA
- 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
SN74AHCT138PWE4 FAQ
1.How can I place an order for SN74AHCT138PWE4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AHCT138PWE4 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 SN74AHCT138PWE4 reliable?
The price and inventory of SN74AHCT138PWE4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AHCT138PWE4 is usually 5 days.
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SN74AHCT138PWE4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74AHCT138PWE4 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 SN74AHCT138PWE4?
For technical support, including SN74AHCT138PWE4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AHCT138PWE4 requirements.
6.How does Aetrix verify that SN74AHCT138PWE4 is sourced from the original manufacturer or authorized distributors?
All SN74AHCT138PWE4 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 SN74AHCT138PWE4 meets industry standards.
7.What is the process for return or replacement of SN74AHCT138PWE4?
All SN74AHCT138PWE4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74AHCT138PWE4, 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 SN74AHCT138PWE4 part is unused and in its original packaging.
Return procedure for SN74AHCT138PWE4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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