My Inquiry
My Account
Texas Instruments CY74FCT138CTQCT
- Part No.:
- CY74FCT138CTQCT
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SSOP (0.154", 3.90mm Width)
- Datasheet:
-
CY74FCT138CTQCT.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16SSOP
- Quantity:
- Payment:
- Shipping:
Inventory:2,673
Please send an inquiry. Send us your inquiry, and we will respond immediately.
Product details
Overview
CY74FCT138CTQCT 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, 5-ns propagation delay (max), and operates from 4.75 V to 5.25 V across –40°C to +85°C - used in address decoding for microcontroller-based memory expansion and I/O port selection.
For engineers reviewing the CY74FCT138CTQCT datasheet, CY74FCT138CTQCT pinout, CY74FCT138CTQCT application, or CY74FCT138CTQCT equivalent, key selection criteria include TTL-compatible input thresholds, Ioff partial-power-down support, matched rise/fall times, edge-rate control for noise immunity, and QSOP-16 package compatibility with space-constrained industrial control PCBs.
Technical Context
The CY74FCT138CTQCT implements combinational logic decoding with dual low-enable (E1, E2) and single high-enable (E3) control, enabling cascaded 1-of-32 decoding using four devices plus one inverter. Its output structure uses totem-pole drivers with controlled edge rates to minimize switching noise.
It features Ioff circuitry that disables outputs when VCC = 0 V, preventing backflow current during partial power-down - critical for hot-swap and mixed-voltage system designs. Input hysteresis (0.2 V) enhances noise immunity on enable and address lines.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Propagation Delay | 5 ns max (A→O or E→O), enabling reliable operation at ≥100 MHz clock-controlled enable/address transitions |
| Output Drive | 64 mA sink / 32 mA source, sufficient to directly drive multiple TTL loads or LED indicators without buffering |
| Supply Voltage | 4.75 V to 5.25 V, ensuring stable operation within standard 5-V ±5% rails and compatibility with legacy TTL systems |
| Input Thresholds | VIL = 0.8 V, VIH = 2.0 V - fully compatible with TTL logic levels and robust against ground bounce |
| Ioff Current | ±1 µA at VCC = 0 V, VOUT = 4.5 V - guarantees safe isolation during power sequencing or standby modes |
| Operating Temperature | –40°C to +85°C, qualified for industrial-grade embedded control and automation equipment |
| ESD Protection | 2000-V HBM, 200-V MM, 1000-V CDM - exceeds JEDEC JESD22 requirements for board-level handling reliability |
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 bus; sampled synchronously with enable asserts to select one of eight outputs |
| 2 (A1) | Binary address input | Middle bit of address; combined with A0/A2 to generate unique 3-bit code for output activation |
| 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 when E1 = high, regardless of other enables |
| 5 (E2) | Enable input (active low) | Secondary low-enable; both E1 and E2 must be low for decode to proceed |
| 6 (E3) | Enable input (active high) | Final gating signal; only when E3 = high do outputs reflect decoded address state |
| 7 (O7) | Active-low output | Output corresponding to A2A1A0 = 111; sinks current when selected and enabled |
| 8 (GND) | Ground reference | Power return path for all internal logic and output drivers; requires low-impedance PCB plane connection |
| 9 (VCC) | Supply voltage | +5 V nominal supply; bypassing with 0.1 µF ceramic capacitor near pin essential for noise suppression |
| 10 (O0) | Active-low output | Output for A2A1A0 = 000; lowest-address output, commonly used for boot device or primary peripheral select |
| 11 (O1) | Active-low output | Output for A2A1A0 = 001; supports sequential peripheral addressing in multi-device systems |
| 12 (O2) | Active-low output | Output for A2A1A0 = 010; enables discrete I/O line assignment in programmable logic interfaces |
| 13 (O3) | Active-low output | Output for A2A1A0 = 011; used in memory-mapped register banks requiring dedicated chip-select lines |
| 14 (O4) | Active-low output | Output for A2A1A0 = 100; supports upper-half peripheral decoding in 16-bit address spaces |
| 15 (O5) | Active-low output | Output for A2A1A0 = 101; facilitates modular expansion of FPGA configuration or CPLD I/O banks |
| 16 (O6) | Active-low output | Output for A2A1A0 = 110; provides dedicated select for auxiliary communication peripherals (e.g., UART, SPI slaves) |
Key Features
| Feature | Design Value |
|---|---|
| Edge-rate controlled outputs | Reduces simultaneous switching noise (SSN) by limiting di/dt, improving signal integrity in dense PCB layouts |
| Ioff partial-power-down support | Enables safe insertion/removal in live backplanes and allows independent power domain sequencing without latch-up risk |
| Matched rise/fall times | Ensures symmetrical output transitions (<1 ns skew), minimizing timing uncertainty in synchronous decode applications |
| TTL-compatible input thresholds | Accepts standard 0.8 V/2.0 V logic levels - eliminates need for level-shifting when interfacing with legacy microcontrollers |
| Three-enable architecture | Supports hierarchical decoding: E1/E2 act as group selects, E3 as local gate - simplifies multi-chip address map partitioning |
Applications
| Memory Address Decoding | Industrial I/O Expansion |
|---|---|
Use Scenario: Selecting one of eight SRAM or EPROM chips in a microcontroller-based data logger with 64 KB address space. IC Role / Device Role / Timing Role: 1-of-8 decoder generating chip-select signals synchronized to address bus and control strobes. Use Value: Enables compact, low-latency memory mapping without FPGA or CPLD - reduces BOM cost and design complexity. | Use Scenario: Driving eight isolated relay modules in a PLC rack via parallel I/O port expansion. IC Role / Device Role / Timing Role: Active-low output driver translating 3-bit port bits into individual relay enable lines. Use Value: Provides 64-mA sink per output to directly energize relay coils, eliminating external transistor arrays. |
| Microcontroller Peripheral Selection | Legacy Bus Interface Logic |
Use Scenario: Assigning unique chip-selects to UART, ADC, DAC, and sensor interfaces on an ARM Cortex-M4 evaluation board. IC Role / Device Role / Timing Role: Address decoder decoding upper address bits to activate specific peripheral address windows. Use Value: Delivers sub-5-ns propagation delay to meet tight setup/hold timing for 50-MHz APB bus cycles. | Use Scenario: Interfacing modern microcontrollers with vintage ISA-bus peripherals requiring TTL-level decode logic. IC Role / Device Role / Timing Role: Level-translation and decoding element ensuring compatibility between 3.3-V MCU GPIO and 5-V ISA address/data paths. Use Value: Full TTL input/output compatibility and 0.2-V hysteresis prevent metastability on noisy industrial backplane signals. |
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 electrical specs; differs only in tape-and-reel packaging (2500 pcs vs CY74FCT138CTQCT's 2500 pcs) and marking (FCT138C vs FT138-3) | No functional difference; suitable for identical use cases including memory decode and I/O expansion | Select SN74FCT138QDR if sourcing from distributors carrying TI's standard FCT portfolio with alternate reel labeling |
| 74ACT138SCX | Advanced CMOS variant: higher VOH (≥4.4 V), lower ICC (0.04 mA), but no Ioff support and 8.5-ns max tPD - lacks partial-power-down capability | Not suitable for hot-swap or mixed-rail systems; acceptable only in always-on, single-supply 5-V designs | Choose 74ACT138SCX only when ultra-low static current is prioritized over power sequencing safety and noise immunity |
Compared with SN74FCT138QDR, CY74FCT138CTQCT offers identical functionality and qualification - differing only in top-side marking and minor packaging logistics. Against 74ACT138SCX, CY74FCT138CTQCT provides critical Ioff protection and superior noise performance at the cost of slightly higher static current, making it the preferred choice for industrial control and power-aware systems.
Availability
CY74FCT138CTQCT is available at Aetrix Electronics and suitable for industrial control panels, microcontroller-based data acquisition systems, and legacy bus interface modules requiring stable component supply, long-lifecycle support, and guaranteed RoHS compliance.
Supply support for CY74FCT138CTQCT 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.
CY74FCT138CTQCT belongs to the 74FCT logic family - designed specifically for high-speed, low-noise, TTL-compatible decoding in industrial and instrumentation applications where reliability under ESD stress and power sequencing robustness are mandatory.
FAQ
What is the maximum propagation delay of the CY74FCT138CTQCT at 5 V?
The CY74FCT138CTQCT has a maximum propagation delay of 5 ns (tPLH/tPHL) from any address (A0–A2) or enable (E1–E3) input to any output (O0–O7) under recommended operating conditions (VCC = 4.75 V to 5.25 V, TA = –40°C to +85°C). This value is specified for the "C" speed grade and confirmed in the switching characteristics table of the official TI datasheet SCCS013B.
Does the CY74FCT138CTQCT support partial power-down operation?
Yes, the CY74FCT138CTQCT supports partial power-down via its Ioff feature. When VCC = 0 V, the outputs are disabled and leakage is limited to ±1 µA even with up to 4.5 V applied at output pins - preventing damaging current backflow during power sequencing or hot-swap events. This behavior is explicitly characterized in the electrical characteristics table.
What package type and dimensions does the CY74FCT138CTQCT use?
The CY74FCT138CTQCT uses a QSOP-16 (DBQ) package: 3.9 mm × 4.9 mm body size, 0.65 mm lead pitch, 1.0 mm max height, and NiPdAu lead finish. It is RoHS-compliant, moisture sensitivity level (MSL) 2 (260°C peak reflow, 1-year floor life), and supplied in 2500-piece tape-and-reel format per TI's packaging addendum.
Can the CY74FCT138CTQCT directly drive TTL loads?
Yes, the CY74FCT138CTQCT can directly drive standard TTL loads: its 64-mA sink and 32-mA source capability exceeds the 16-mA sink / 0.4-mA source requirement of LS-TTL, and its VIH/VIL thresholds (2.0 V / 0.8 V) match TTL logic levels. No external buffers are needed for interfacing with 74LS, 74ALS, or legacy microcontroller GPIOs.
How many enable inputs does the CY74FCT138CTQCT have, and what are their polarities?
The CY74FCT138CTQCT has three enable inputs: E1 and E2 are active-low, while E3 is active-high. All three must be asserted simultaneously (E1 = L, E2 = L, E3 = H) for decoding to occur; otherwise, all outputs remain high. This triple-enable architecture enables flexible hierarchical decoding, such as grouping multiple decoders in larger address maps.
CY74FCT138CTQCT 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
CY74FCT138CTQCT FAQ
1.How can I place an order for CY74FCT138CTQCT through Aetrix?
Please submit a Request for Quotation (RFQ) for CY74FCT138CTQCT 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 CY74FCT138CTQCT reliable?
The price and inventory of CY74FCT138CTQCT are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for CY74FCT138CTQCT is usually 5 days.
3.What payment methods are accepted for CY74FCT138CTQCT?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for CY74FCT138CTQCT transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for CY74FCT138CTQCT?
CY74FCT138CTQCT orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your CY74FCT138CTQCT 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 CY74FCT138CTQCT?
For technical support, including CY74FCT138CTQCT datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your CY74FCT138CTQCT requirements.
6.How does Aetrix verify that CY74FCT138CTQCT is sourced from the original manufacturer or authorized distributors?
All CY74FCT138CTQCT 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 CY74FCT138CTQCT meets industry standards.
7.What is the process for return or replacement of CY74FCT138CTQCT?
All CY74FCT138CTQCT units undergo pre-shipment inspection (PSI). If there is an issue with CY74FCT138CTQCT, 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 CY74FCT138CTQCT part is unused and in its original packaging.
Return procedure for CY74FCT138CTQCT:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
CY74FCT138CTQCT Tags
-
SN74HC138DR
Texas Instruments
-
TC7SB3157CFU,LF(CT
Toshiba Semiconductor and Storage
-
74CBTLV3257PW,118
Nexperia USA Inc.
-
SN74CBTLV3257PWR
Texas Instruments
-
74CBTLV3257GUX
Nexperia USA Inc.
-
74HC154BQ,118
Nexperia USA Inc.
-
P3S0200GMX
NXP USA Inc.
-
SN74CB3Q3245PWR
Texas Instruments
-
SN74CB3Q3257RGYR
Texas Instruments
-
TCA9543APWR
Texas Instruments
-
TCA9546APWR
Texas Instruments
-
SN74HC138N
Texas Instruments
Tech Hub
A practical engineering guide to 3.3V and 5V logic compatibility, input thresholds, resistor dividers, translator ICs, MOSFET level shifting, I2C pull-ups, timing limits and power-sequencing risks.
The 74HC595 uses push-pull logic outputs, while the TPIC6B595 uses 50 V open-drain DMOS sinks for higher-power loads. This guide compares timing, current limits, 3.3 V interfacing, load wiring, thermal…
The 74HC595 converts serial data into eight stable parallel outputs. This guide covers pin functions, shift and storage timing, OE and MR behavior, drive-current limits, cascading, voltage compatibilit…
A technical comparison of level-sensitive latches and edge-triggered flip-flops, covering timing windows, setup and hold limits, master–slave operation, time borrowing, race-through, HDL inference and…
A D latch stores one bit while Enable controls when data can pass. This reference covers gate-level operation, truth tables, transparency, setup and hold timing, LE versus OE, common ICs and practical …
An SR latch stores one bit through cross-coupled feedback. This engineering reference covers NOR and NAND implementations, truth tables, forbidden-state recovery, gated operation, switch debouncing, fa…
Latch circuits retain one bit through feedback. This technical reference covers SR and D latches, truth tables, transparency, timing limits, latch-versus-flip-flop behavior, applications and common log…
An engineering guide to LED driver operation, constant-current and constant-voltage outputs, linear and switching topologies, dimming, IC selection, calculations, replacement compatibility, and fault c…
Operational amplifier guide covering op amp basics, feedback, ideal vs real op amps, common configurations, buffer circuits, offset, bias current, gain-bandwidth, slew rate, rail-to-rail limits and sel…
Jumper cables guide covering safe connection order, red and black clamp placement, final ground connection, cable gauge, length, clamp quality, copper vs CCA cables, jump starter comparison and battery…
