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STMicroelectronics 74LCX138TTR
- Part No.:
- 74LCX138TTR
- Manufacturer:
- STMicroelectronics
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-TSSOP (0.173", 4.40mm Width)
- Datasheet:
-
74LCX138TTR.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:1,007
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Product details
Overview
74LCX138TTR from STMicroelectronics is a low-voltage CMOS 3-to-8 line inverting decoder with 5V-tolerant inputs, operating from 2.0V to 3.6V, delivering 6.7ns max propagation delay at 3V and ±24mA output drive, used in memory address decoding and bus interface logic for 3.3V systems interfacing with 5V peripherals.
For engineers reviewing the 74LCX138TTR datasheet, 74LCX138TTR pinout, 74LCX138TTR application, or 74LCX138TTR equivalent, key selection criteria include 5V input tolerance, symmetrical 24mA output drive capability, latch-up immunity >500mA, and SO-16/TSSOP16 package compatibility with legacy 74-series decoders.
Technical Context
The device implements a fully decoded 3-input (A/B/C) inverting logic function with three enable inputs (G1, G2A, G2B) enabling hierarchical cascade in multi-chip memory systems. Its C2MOS sub-micron fabrication ensures balanced tPLH ≅ tPHL propagation delays and power-down protection on all I/Os.
Input voltage range spans 0–5.5V independent of VCC, allowing safe interfacing with 5V TTL/CMOS signals while powered at 3.3V. Output stage delivers matched |IOH| = IOL = 24mA (min) at VCC = 3.0–3.6V, meeting PCI bus drive requirements without external buffers.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Operating Range | 2.0V to 3.6V - Enables direct integration into 3.3V logic domains without level shifters. |
| tPD (Max) | 6.7ns at VCC = 3.0–3.6V - Matches AC/ACT-138 speed at half the supply voltage. |
| Input Tolerance | 0V to 5.5V - Allows direct connection to 5V buses without external clamping or translation. |
| IOL / IOH (Min) | ±24mA at VCC = 3.0–3.6V - Drives standard PCI loads and multiple LVTTL inputs. |
| ESD Rating | HBM > 2000V - Ensures robust handling during board assembly and system integration. |
| Latch-up Immunity | >500mA per JESD17 - Guarantees reliability under transient overvoltage conditions. |
Pinout & Package
TSSOP16 (Thin Shrink Small Outline Package, 4.4mm × 5.0mm body, 0.65mm pitch) - RoHS-compliant, ECOPACK®-certified lead-free package optimized for high-density PCB layouts.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1,2,3 (A,B,C) | Binary address select inputs | Determine active-low output Y0–Y7; accept 0–5.5V logic levels regardless of VCC. |
| 4,5 (G2A,G2B) | Active-high enable inputs | Both must be low to activate decode; enables cascading via OR-ing of upstream enables. |
| 6 (G1) | Active-low enable input | Must be high to enable; complements G2A/G2B for flexible hierarchical enable tree design. |
| 7,9–15 (Y0–Y7) | Inverting decoded outputs | Only one output goes low per valid input combination; all high when disabled. |
| 8 (GND) | Ground reference | 0V return path for all internal logic and output drivers; requires low-impedance PCB plane. |
| 16 (VCC) | Positive supply | Supplies core logic and output stages; bypassing with 100nF ceramic near pin is mandatory for noise immunity. |
Key Features
| Feature | Design Value |
|---|---|
| 5V-tolerant inputs | Supports mixed-voltage system integration without external level translators or resistors. |
| Symmetrical 24mA drive | Eliminates need for external pull-ups/pull-downs in PCI and LVTTL fanout applications. |
| Power-down I/O protection | Prevents back-driving and current leakage when VCC = 0V, critical for hot-swap and partial-power-down systems. |
| Matched tPLH/tPHL | Reduces timing skew across outputs, simplifying synchronous bus timing closure in memory controllers. |
Applications
| Memory Address Decoding | PCI Bus Interface Logic |
|---|---|
Use Scenario: Selecting one of eight memory banks in a 32-bit embedded microcontroller system with 3.3V core and 5V peripheral bus. IC Role / Device Role / Timing Role: Inverting 3-to-8 decoder providing chip-select signals with 6.7ns propagation delay and 5V-tolerant address lines. Use Value: Eliminates need for discrete level shifters while maintaining full-speed access to legacy 5V SRAM/Flash devices. | Use Scenario: Enabling individual I/O slots in a compact industrial PCI-compatible expansion chassis. IC Role / Device Role / Timing Role: Cascadeable address decoder generating slot-select signals compliant with PCI DC specifications (24mA drive, 0.55V VOL). Use Value: Meets PCI bus electrical requirements directly-no additional buffer ICs required for slot enable generation. |
| Low-Power FPGA I/O Expansion | Industrial PLC I/O Multiplexing |
Use Scenario: Expanding GPIO count from a battery-powered FPGA by driving 8-channel analog mux control lines. IC Role / Device Role / Timing Role: Low-static-current (10µA ICC) decoder translating FPGA 3.3V outputs to enable 5V-tolerant analog switch arrays. Use Value: Reduces system standby power vs. standard 74AC138 while preserving compatibility with 5V analog front-ends. | Use Scenario: Routing sensor input channels to a single ADC in a DIN-rail mounted programmable logic controller. IC Role / Device Role / Timing Role: Robust address decoder operating across –40°C to +85°C with >500mA latch-up immunity for factory-floor reliability. Use Value: Withstands ESD events and supply transients common in industrial environments without protection circuitry overhead. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar 3-to-8 inverting decoder applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| 74LVC138AD,118 (Nexperia) | Lower ICC (4µA), identical 5V-tolerant inputs and TSSOP16 package, but tPD = 7.2ns (max) at 3.3V. | Marginally slower propagation; suitable where ultra-low quiescent current outweighs 0.5ns timing budget. | Select when minimizing sleep-mode power is prioritized over worst-case timing margin. |
| SN74LV138APWR (TI) | Same 2.0–5.5V VCC range and 24mA drive, but only 3.3V-tolerant inputs (not 5V-tolerant); SOIC-16 only. | Requires external level shifting for 5V signal sources; incompatible with direct 5V bus interfacing. | Choose only in 3.3V-only systems where footprint compatibility with SOIC-16 is mandatory. |
Compared with 74LVC138AD and SN74LV138APWR, the 74LCX138TTR uniquely combines true 5V input tolerance, 6.7ns speed at 3V, and TSSOP16 packaging-making it the sole option for space-constrained, mixed-voltage memory decode requiring guaranteed PCI-level drive and latch-up immunity.
Availability
74LCX138TTR is available at Aetrix Electronics and suitable for memory address decoding, PCI bus interface logic, and low-power FPGA I/O expansion requiring stable component supply and long-term industrial lifecycle support.
Supply support for 74LCX138TTR 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
STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing silicon solutions for automotive, industrial, and consumer markets since 1987.
The 74LCX logic family was engineered specifically for high-speed, low-voltage 3.3V operation with 5V-tolerant I/O-targeting next-generation embedded systems needing backward compatibility with legacy 5V peripherals without performance or power penalties.
FAQ
Is 74LCX138TTR pin-compatible with standard 74HC138 or 74LS138?
Yes-74LCX138TTR maintains identical pinout and Boolean function (inverting 3-to-8 decode) with 74HC138 and 74LS138, including A/B/C address inputs, G1/G2A/G2B enables, and Y0–Y7 outputs. However, its 5V-tolerant inputs and 3.3V-only VCC range require careful power domain isolation versus 5V-supplied legacy variants.
What is the maximum capacitive load this device can drive reliably?
The 74LCX138TTR is characterized up to 50pF load capacitance per output (per AC specs table), with guaranteed tPLH/tPHL ≤6.7ns at VCC = 3.0–3.6V. Driving >50pF increases propagation delay nonlinearly and may cause ringing; for >70pF loads, add series termination or use a buffer stage.
Does this part support partial power-down operation?
Yes-the 74LCX138TTR features power-down protection on all inputs and outputs, allowing VCC = 0V while inputs remain at 0–5.5V without damaging the device or injecting current into the supply rail. This enables safe hot-plug operation in modular backplane systems.
Can G2A and G2B be tied together for simplified enable control?
Yes-G2A and G2B are both active-high enables; tying them together reduces enable logic complexity. However, doing so eliminates independent control of cascaded sections. When tied, ensure the combined node meets VIH ≥2.0V and VIL ≤0.8V under all operating conditions, including bus leakage.
74LCX138TTR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Series:
- 74LCX
- Package/Case:
- 16-TSSOP (0.173", 4.40mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Type:
- Decoder/Demultiplexer
- Circuit:
- 1 x 3:8
- Independent Circuits:
- 1
- Current - Output High, Low:
- 24mA, 24mA
- Voltage Supply Source:
- Single Supply
- Voltage - Supply:
- 2V ~ 3.6V
- Operating Temperature:
- -40°C ~ 85°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-TSSOP
74LCX138TTR FAQ
1.How can I place an order for 74LCX138TTR through Aetrix?
Please submit a Request for Quotation (RFQ) for 74LCX138TTR 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 74LCX138TTR reliable?
The price and inventory of 74LCX138TTR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 74LCX138TTR is usually 5 days.
3.What payment methods are accepted for 74LCX138TTR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 74LCX138TTR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for 74LCX138TTR?
74LCX138TTR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your 74LCX138TTR 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 74LCX138TTR?
For technical support, including 74LCX138TTR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 74LCX138TTR requirements.
6.How does Aetrix verify that 74LCX138TTR is sourced from the original manufacturer or authorized distributors?
All 74LCX138TTR 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 74LCX138TTR meets industry standards.
7.What is the process for return or replacement of 74LCX138TTR?
All 74LCX138TTR units undergo pre-shipment inspection (PSI). If there is an issue with 74LCX138TTR, 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 74LCX138TTR part is unused and in its original packaging.
Return procedure for 74LCX138TTR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
74LCX138TTR 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
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