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Texas Instruments CY74FCT138TQCT
- Part No.:
- CY74FCT138TQCT
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SSOP (0.154", 3.90mm Width)
- Datasheet:
-
CY74FCT138TQCT.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16SSOP
- Quantity:
- Payment:
- Shipping:
Inventory:1,060
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Product details
Overview
CY74FCT138TQCT from Texas Instruments is a 1-of-8 active-low decoder IC with three binary address inputs (A0–A2), three enable inputs (E1, E2 low-active; E3 high-active), and eight mutually exclusive active-low outputs (O0–O7). It delivers 64-mA sink / 32-mA source drive strength, operates from 4.75 V to 5.25 V, and supports partial-power-down via Ioff. It is used in memory address decoding, peripheral selection, and bus demultiplexing in industrial control and embedded systems.
For engineers reviewing the CY74FCT138TQCT datasheet, CY74FCT138TQCT pinout, CY74FCT138TQCT application, or CY74FCT138TQCT equivalent, key selection criteria include its 9 ns max propagation delay (A→O), TTL-compatible input thresholds, 0.55 V max VOL at 64 mA, edge-rate controlled outputs for noise immunity, and QSOP-16 package suitability for space-constrained PCB layouts.
Technical Context
This device implements combinational logic decoding using standard positive-logic NAND-gate architecture with enable gating. All outputs are high-impedance when disabled, and only one output goes low per valid input combination when E1=E2=L and E3=H. Its Ioff circuitry ensures <±1 µA backflow current when VCC = 0 V, enabling safe hot-insertion and multi-rail power sequencing.
It features matched rise/fall times and edge-rate control to minimize simultaneous switching noise (SSN). Input hysteresis is 0.2 V, and it meets JESD22 ESD ratings: 2000-V HBM, 200-V MM, and 1000-V CDM - confirming robustness in industrial environments.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage | 4.75 V to 5.25 V - ensures compatibility with 5-V TTL and mixed-voltage logic systems without level shifters. |
| Max Propagation Delay | 9 ns (A→O) - enables reliable operation in high-speed address decode paths up to ~110 MHz clock-equivalent timing. |
| Output Drive | 64 mA sink / 32 mA source - drives multiple TTL loads or LED indicators directly without buffers. |
| VOL / VOH | 0.55 V max at 64 mA sink; 2.4 V min at –32 mA source - guarantees clean logic-level margins across temperature and load. |
| Ioff Current | ±1 µA at VCC = 0 V - prevents backfeed damage during partial power-down or board hot-swap scenarios. |
| Input Hysteresis | 0.2 V - improves noise immunity on enable and address lines in electrically noisy industrial settings. |
| ESD Rating | 2000-V HBM - exceeds industrial IEC 61000-4-2 system-level ESD immunity requirements for front-panel interfaces. |
Pinout & Package
Package: QSOP-16 (DBQ), 3.9 mm × 4.9 mm body, 0.65 mm pitch, RoHS-compliant NiPdAu lead finish, MSL Level-2-260°C-1 year.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (A0) | Binary address input | LSB of 3-bit address; sampled synchronously with enable conditions to select one of eight outputs. |
| 2 (A1) | Binary address input | Middle bit of address; combined with A0/A2 to determine active output O0–O7. |
| 3 (A2) | Binary address input | MSB of address; defines higher-order output group (O0–O3 vs O4–O7). |
| 4 (E1) | Enable input (active low) | Primary global enable; all outputs forced high unless E1 = L, E2 = L, and E3 = H. |
| 5 (E2) | Enable input (active low) | Secondary enable; used with E1/E3 for hierarchical decoding (e.g., 1-of-32 expansion with inverter). |
| 6 (E3) | Enable input (active high) | Positive-logic enable; allows direct connection to microcontroller GPIO or bus controller signals. |
| 7 (O7) | Active-low decoded output | Asserts low when A2A1A0 = 111 and enables active - used for chip-select or interrupt assertion. |
| 8 (GND) | Ground reference | Return path for all internal logic and output currents; must be low-impedance for noise control. |
| 9 (VCC) | Power supply | 5-V nominal supply; decoupling capacitor (0.1 µF) required within 5 mm for stable switching performance. |
| 10 (O0) | Active-low decoded output | Asserts low when A2A1A0 = 000 - typically assigned to boot ROM or primary peripheral CS. |
| 11 (O1) | Active-low decoded output | Asserts low when A2A1A0 = 001 - commonly used for UART or timer peripheral selection. |
| 12 (O2) | Active-low decoded output | Asserts low when A2A1A0 = 010 - supports discrete I/O expander or ADC interface addressing. |
| 13 (O3) | Active-low decoded output | Asserts low when A2A1A0 = 011 - enables dual-bank memory mapping or sensor array selection. |
| 14 (O4) | Active-low decoded output | Asserts low when A2A1A0 = 100 - used in FPGA configuration or CPLD address decode trees. |
| 15 (O5) | Active-low decoded output | Asserts low when A2A1A0 = 101 - supports legacy ISA-style I/O port decoding. |
| 16 (O6) | Active-low decoded output | Asserts low when A2A1A0 = 110 - assigned to watchdog or debug interface enable in safety-critical designs. |
Key Features
| Feature | Design Value |
|---|---|
| Edge-rate controlled outputs | Reduces simultaneous switching noise by limiting dV/dt - critical for meeting CISPR 22 Class B emissions in compact enclosures. |
| Ioff partial-power-down support | Enables safe isolation of powered-down subsystems without disabling upstream logic - essential for modular power management. |
| Matched rise/fall times | Minimizes duty-cycle distortion on decoded strobes - preserves timing integrity in synchronous bus arbitration. |
| TTL-compatible input thresholds | Accepts standard 0.8 V/2.0 V VIH/VIL levels - eliminates need for external level translators when interfacing with legacy microcontrollers. |
| Three-enable architecture | Allows cascading four devices + one inverter to build 1-of-32 decoder - reduces component count versus discrete gate solutions. |
Applications
| Memory Address Decoding | Peripheral Selection |
|---|---|
Use Scenario: Selecting between eight SRAM, EPROM, or flash memory banks in an 8-bit microcontroller system with 16-bit address bus. IC Role / Device Role / Timing Role: Translates A0–A2 and enable signals into individual chip-select (CS#) lines with sub-10 ns latency. Use Value: Enables deterministic memory access timing and eliminates address decoding race conditions in real-time firmware. | Use Scenario: Assigning dedicated I/O addresses to UART, SPI, I²C, timer, ADC, DAC, GPIO expander, and watchdog peripherals. IC Role / Device Role / Timing Role: Generates active-low peripheral enable signals synchronized to bus cycle timing and address strobes. Use Value: Reduces glue logic count and simplifies PCB routing compared to discrete NAND-based decoding. |
| Bus Demultiplexing | Industrial Control Logic |
Use Scenario: Routing a shared data bus to one of eight sensor nodes or actuator drivers in a PLC backplane. IC Role / Device Role / Timing Role: Acts as a hardware-controlled 1:8 data path selector, driven by master controller address lines. Use Value: Provides deterministic, low-jitter signal routing without software overhead or CPU intervention. | Use Scenario: Implementing safety interlock logic where eight machine zones require independent enable/disable control. IC Role / Device Role / Timing Role: Converts zone ID bits and master enable into isolated, current-sinking fault-clear signals. Use Value: Delivers 64-mA drive capability to directly energize relay coils or optocoupler LEDs without external drivers. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar 1-of-8 decoder applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74FCT138QDR | Same FCT family, identical pinout and logic function; 5.5-V absolute max rating vs 5.25-V recommended max for CY74FCT138TQCT. | Broader supply margin supports legacy 5.5-V systems; otherwise drop-in compatible in new designs. | Select when operating near 5.5 V or requiring TI's newer packaging and qualification. |
| 74ACT138SCX | ACT family: higher speed (max 8 ns), 5-V only, no Ioff, lower drive (24 mA sink), higher ICC. | Lacks partial-power-down support; unsuitable for hot-swap or multi-rail systems requiring Ioff. | Choose only for pure speed-critical, single-rail 5-V applications where Ioff is irrelevant. |
Compared with SN74FCT138QDR and 74ACT138SCX, CY74FCT138TQCT offers optimal balance of industrial-grade noise immunity, Ioff-enabled power sequencing, and proven reliability in long-lifecycle embedded deployments - making it preferred for automotive ECUs, medical instruments, and factory automation controllers.
Availability
CY74FCT138TQCT is available at Aetrix Electronics and suitable for memory address decoding, peripheral selection, bus demultiplexing, industrial control logic, and safety interlock systems requiring stable component supply across extended product lifecycles.
Supply support for CY74FCT138TQCT 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 for industrial, automotive, and communications markets.
CY74FCT138TQCT belongs to the FCT logic family designed for high-noise-immunity, TTL-compatible 5-V digital systems with emphasis on industrial reliability, low power-down leakage, and robust ESD performance.
FAQ
What is the maximum propagation delay of CY74FCT138TQCT under recommended operating conditions?
The maximum propagation delay for CY74FCT138TQCT is 9 ns (from any address or enable input to output), measured under recommended conditions: VCC = 4.75 V to 5.25 V, TA = –40°C to 85°C, and CL = 50 pF. This value applies to both tPLH and tPHL transitions and ensures timing compliance in high-speed 5-V bus systems.
Does CY74FCT138TQCT support partial-power-down operation, and how is it implemented?
Yes, CY74FCT138TQCT supports partial-power-down via its Ioff circuitry. When VCC = 0 V, Ioff limits current flow to ±1 µA regardless of input/output voltage levels, preventing damaging back-current during hot-swap or multi-rail sequencing. This feature is intrinsic to the silicon design and requires no external control.
What package type and footprint does CY74FCT138TQCT use, and is it RoHS-compliant?
CY74FCT138TQCT uses the QSOP-16 (DBQ) package: 3.9 mm × 4.9 mm body, 0.65 mm lead pitch, NiPdAu lead finish. It is RoHS-compliant (lead-free), rated MSL Level-2-260°C-1 year, and supplied in 2500-piece tape-and-reel format - suitable for automated SMT assembly.
Can CY74FCT138TQCT directly drive TTL loads, and what is its fanout capability?
Yes, CY74FCT138TQCT can directly drive standard TTL loads. With 64-mA sink and 32-mA source capability, it supports ≥10 standard TTL unit loads (each ~1.6 mA) per output. Its VOH ≥2.4 V and VOL ≤0.55 V at full drive ensure robust noise margins across temperature and supply variation.
How does the three-enable architecture of CY74FCT138TQCT improve system scalability?
The CY74FCT138TQCT's dual low-active (E1, E2) and single high-active (E3) enables allow hierarchical expansion: four devices plus one inverter create a 1-of-32 decoder without additional logic gates. This reduces component count, PCB area, and signal routing complexity in large-address-space systems like industrial HMIs or test equipment.
CY74FCT138TQCT Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74FCT
- Package/Case:
- 16-SSOP (0.154", 3.90mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Type:
- Decoder/Demultiplexer
- Circuit:
- 1 x 3:8
- Independent Circuits:
- 1
- Current - Output High, Low:
- 32mA, 64mA
- Voltage Supply Source:
- Single Supply
- Voltage - Supply:
- 4.75V ~ 5.25V
- Operating Temperature:
- -40°C ~ 85°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SSOP
CY74FCT138TQCT FAQ
1.How can I place an order for CY74FCT138TQCT through Aetrix?
Please submit a Request for Quotation (RFQ) for CY74FCT138TQCT 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 CY74FCT138TQCT reliable?
The price and inventory of CY74FCT138TQCT are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for CY74FCT138TQCT is usually 5 days.
3.What payment methods are accepted for CY74FCT138TQCT?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for CY74FCT138TQCT transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for CY74FCT138TQCT?
CY74FCT138TQCT orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your CY74FCT138TQCT 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 CY74FCT138TQCT?
For technical support, including CY74FCT138TQCT datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your CY74FCT138TQCT requirements.
6.How does Aetrix verify that CY74FCT138TQCT is sourced from the original manufacturer or authorized distributors?
All CY74FCT138TQCT 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 CY74FCT138TQCT meets industry standards.
7.What is the process for return or replacement of CY74FCT138TQCT?
All CY74FCT138TQCT units undergo pre-shipment inspection (PSI). If there is an issue with CY74FCT138TQCT, 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 CY74FCT138TQCT part is unused and in its original packaging.
Return procedure for CY74FCT138TQCT:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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