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Texas Instruments CY74FCT138ATQCT
- Part No.:
- CY74FCT138ATQCT
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SSOP (0.154", 3.90mm Width)
- Datasheet:
-
CY74FCT138ATQCT.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16SSOP
- Quantity:
- Payment:
- Shipping:
Inventory:2,964
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Product details
Overview
CY74FCT138ATQCT 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 achieves 5.8 ns max propagation delay across –40°C to +85°C. It serves in address decoding for microprocessor-based memory and I/O expansion systems.
For engineers reviewing the CY74FCT138ATQCT datasheet, CY74FCT138ATQCT pinout, CY74FCT138ATQCT application, or CY74FCT138ATQCT equivalent, key selection criteria include TTL-compatible input thresholds, Ioff partial-power-down support, edge-rate controlled noise immunity, matched rise/fall times, and QSOP-16 package compatibility with space-constrained industrial control logic.
Technical Context
The CY74FCT138ATQCT implements combinational logic decoding using standard positive-logic NAND-gate architecture with triple-enable gating (E1·E2·E3). Its output stage uses FCT-series totem-pole drivers optimized for 5-V TTL/CMOS interfacing, with built-in edge-rate control circuitry to suppress simultaneous switching noise.
It supports partial-power-down via Ioff, which disables all outputs when VCC = 0 V to prevent backflow current. All inputs tolerate 7-V absolute maximum voltage, and outputs are specified for 0.3 V VOL at 64 mA sink and 2.4 V VOH at 32 mA source under nominal 5-V operation.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Propagation Delay | Max 5.8 ns (A→O or E→O) ensures tight timing margins in high-speed address decode paths. |
| Output Drive | 64-mA sink / 32-mA source enables direct driving of multiple TTL loads without buffers. |
| Supply Voltage | 4.75 V to 5.25 V range guarantees robust operation under noisy 5-V rail conditions. |
| Ioff Support | Active at VCC = 0 V; limits backfeed current to ±1 µA, enabling hot-swap and power sequencing safety. |
| Input Thresholds | VIL = 0.8 V, VIH = 2.0 V - fully compatible with legacy TTL logic families. |
| ESD Protection | 2000-V HBM, 200-V MM, 1000-V CDM - meets industrial-grade reliability requirements. |
Pinout & Package
Package: SSOP-16 (DBQ), 5.3 mm × 6.2 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; determines upper/lower half of output group (O0–O3 vs O4–O7). |
| 4 (E1) | Enable input (active low) | Primary global disable; 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 or cascading with other '138 devices. |
| 6 (E3) | Enable input (active high) | Third-level enable; allows flexible logic partitioning-e.g., E3 tied to CPU RD/WR strobe. |
| 7 (O7) | Active-low decoded output | Asserted only when A2A1A0 = 111 AND E1=E2=L, E3=H; drives external latch or chip-select line. |
| 8 (GND) | Ground reference | Return path for all internal logic and output currents; requires low-inductance PCB connection. |
| 9 (VCC) | Power supply | 5-V supply input; bypassing with 0.1 µF ceramic capacitor near pin essential for noise suppression. |
| 10 (O0) | Active-low decoded output | Asserted only when A2A1A0 = 000 AND enables satisfied; commonly used for boot ROM or peripheral base address. |
| 11 (O1) | Active-low decoded output | Asserted on A2A1A0 = 001; supports modular I/O mapping in multi-slot backplane designs. |
| 12 (O2) | Active-low decoded output | Asserted on A2A1A0 = 010; enables discrete function blocks like UART or timer peripherals. |
| 13 (O3) | Active-low decoded output | Asserted on A2A1A0 = 011; used in memory bank selection where lower 4K segments require dedicated CS. |
| 14 (O4) | Active-low decoded output | Asserted on A2A1A0 = 100; supports expansion slots requiring independent device addressing. |
| 15 (O5) | Active-low decoded output | Asserted on A2A1A0 = 101; facilitates dual-CPU coexistence by isolating shared resource access windows. |
| 16 (O6) | Active-low decoded output | Asserted on A2A1A0 = 110; provides chip-select for FPGA configuration memory or boot flash. |
Key Features
| Feature | Design Value |
|---|---|
| Edge-rate controlled outputs | Reduces simultaneous switching noise (SSN) by limiting dV/dt, improving signal integrity in dense logic layouts. |
| Ioff partial-power-down | Enables safe insertion/removal in live-backplane systems without damaging downstream components. |
| Matched rise/fall times | Ensures symmetrical waveform edges, minimizing duty-cycle distortion in timing-critical decode paths. |
| TTL-compatible input levels | Accepts standard 0.8 V/2.0 V thresholds-no level-shifting needed when interfacing with legacy 74LS or 74ALS devices. |
| 3-state compatible architecture | Outputs go high-impedance only when disabled (not inherent 3-state), but enable logic allows bus sharing via external gating. |
Applications
| Memory Address Decoding | Peripheral Interface Selection |
|---|---|
Use Scenario: Selecting one of eight 32-KB RAM/ROM banks in an 80C51 or Z80-based embedded controller. IC Role / Device Role / Timing Role: Primary address decoder mapping A15–A13 to eight chip-select lines; operates within 5.8 ns setup window before memory access strobe. Use Value: Eliminates discrete gate logic, reduces board area, and maintains deterministic decode latency across temperature and voltage. | Use Scenario: Assigning unique chip-select signals to UART, SPI flash, ADC, and CAN transceiver on a single microcontroller bus. IC Role / Device Role / Timing Role: Static I/O mapper generating non-overlapping active-low enables synchronized to MCU address latch pulse. Use Value: Prevents bus contention during peripheral initialization and supports hot-plug detection via E1/E2 control sequencing. |
| Multi-Device Expansion | Industrial Control Logic |
Use Scenario: Building a 1-of-32 decoder using four CY74FCT138ATQCT devices and one inverter for large-scale PLC I/O modules. IC Role / Device Role / Timing Role: Cascaded decoder stage where upper address bits select device, lower bits select output within device. Use Value: Achieves full 32-line decode with <5.8 ns per stage delay and no added skew between parallel outputs. | Use Scenario: Enabling safety-critical relay drivers or sensor multiplexers in factory automation panels operating at –40°C to +85°C. IC Role / Device Role / Timing Role: Fault-tolerant enable distributor routing watchdog-triggered reset signals to isolated subsystems. Use Value: Ioff protection prevents backfeed during partial system shutdown; ESD ratings ensure resilience in electrically noisy environments. |
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 |
|---|---|---|---|
| CY74FCT138CTQCT | 5 ns max propagation delay (vs 5.8 ns); identical pinout, drive strength, and package. | Suitable for tighter timing budgets where sub-6 ns decode latency is required. | Select when system clock period demands minimal decode overhead-e.g., >80 MHz bus cycles. |
| SN74FCT138QDR | Same logic function, 5.5 ns max delay, SOIC-16 package; lower drive (32-mA sink/12-mA source). | Better suited for low-power, low-load applications where fanout ≤ 4 TTL units is sufficient. | Choose for cost-sensitive designs with relaxed drive needs and existing SOIC footprint reuse. |
Compared with CY74FCT138CTQCT, the CY74FCT138ATQCT trades 0.8 ns of speed for broader voltage margin (4.75–5.25 V vs 4.5–5.5 V); versus SN74FCT138QDR, it delivers double the sink current for driving heavier loads without external buffers.
Availability
CY74FCT138ATQCT is available at Aetrix Electronics and suitable for industrial control logic, memory address decoding, peripheral interface selection, and multi-device expansion requiring stable component supply across extended temperature ranges.
Supply support for CY74FCT138ATQCT 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 delivering analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.
The CY74FCT138ATQCT belongs to TI's FCT logic family-designed specifically for high-speed, low-noise 5-V TTL/CMOS interoperability in mission-critical digital systems.
FAQ
What is the maximum propagation delay of the CY74FCT138ATQCT at 5 V and 25°C?
The CY74FCT138ATQCT has a maximum propagation delay of 5.8 ns from any address or enable input to output under recommended operating conditions (VCC = 4.75 V to 5.25 V, TA = –40°C to +85°C). At 25°C and nominal 5 V, typical delay is lower-around 3.5 ns-but design must use the 5.8 ns worst-case value for timing closure.
Does the CY74FCT138ATQCT support partial-power-down mode, and how is it implemented?
Yes, the CY74FCT138ATQCT supports partial-power-down via its Ioff feature. When VCC = 0 V, the Ioff circuitry disables all outputs, limiting backflow current to ±1 µA-even if input/output voltages exceed VCC. This protects powered-down sections in mixed-voltage or hot-swap systems and is confirmed in the datasheet's electrical characteristics table.
What are the absolute maximum voltage ratings for inputs and outputs of the CY74FCT138ATQCT?
The CY74FCT138ATQCT specifies absolute maximum DC input and output voltage ratings of –0.5 V to 7 V relative to GND. This tolerance allows safe interfacing with higher-voltage logic families or transient-suppressed signals without clamping diodes or external protection-provided VCC remains within its 4.75–5.25 V operating range.
Can the CY74FCT138ATQCT be used in cascaded 1-of-32 decoder configurations, and what external component is required?
Yes, the CY74FCT138ATQCT is explicitly designed for cascading: its three enable inputs (E1, E2 low-active; E3 high-active) allow hierarchical expansion. To build a 1-of-32 decoder, four CY74FCT138ATQCT devices plus one inverter are required-the inverter converts a master address bit to generate complementary enables across the group, as documented in the functional description and logic diagram.
Is the CY74FCT138ATQCT pin-compatible with older 74FCT138 variants, and which packages share identical pinouts?
Yes, the CY74FCT138ATQCT is functionally and pin-compatible with CY74FCT138T and CY74FCT138CT in the same SSOP-16 (DBQ) package. Pin assignments for A0–A2, E1–E3, O0–O7, VCC, and GND match exactly across these variants-enabling drop-in replacement where speed or drive strength requirements align with the 'A' grade specification.
CY74FCT138ATQCT 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
CY74FCT138ATQCT FAQ
1.How can I place an order for CY74FCT138ATQCT through Aetrix?
Please submit a Request for Quotation (RFQ) for CY74FCT138ATQCT 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 CY74FCT138ATQCT reliable?
The price and inventory of CY74FCT138ATQCT are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for CY74FCT138ATQCT is usually 5 days.
3.What payment methods are accepted for CY74FCT138ATQCT?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for CY74FCT138ATQCT transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for CY74FCT138ATQCT?
CY74FCT138ATQCT orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your CY74FCT138ATQCT 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 CY74FCT138ATQCT?
For technical support, including CY74FCT138ATQCT datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your CY74FCT138ATQCT requirements.
6.How does Aetrix verify that CY74FCT138ATQCT is sourced from the original manufacturer or authorized distributors?
All CY74FCT138ATQCT 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 CY74FCT138ATQCT meets industry standards.
7.What is the process for return or replacement of CY74FCT138ATQCT?
All CY74FCT138ATQCT units undergo pre-shipment inspection (PSI). If there is an issue with CY74FCT138ATQCT, 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 CY74FCT138ATQCT part is unused and in its original packaging.
Return procedure for CY74FCT138ATQCT:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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