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Texas Instruments CD74HCT238M
- Part No.:
- CD74HCT238M
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
CD74HCT238M.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:9,525
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Product details
Overview
CD74HCT238M from Texas Instruments is a high-speed CMOS 3-to-8 line decoder/demultiplexer with active-high outputs, designed for memory address decoding and data routing in industrial control and embedded systems. It operates at 4.5–5.5 V, delivers 14 ns typical propagation delay (VCC = 4.5 V, CL = 15 pF), supports -55°C to +125°C temperature range, and features three enable inputs (G2, G1, G0) for cascading.
For engineers reviewing the CD74HCT238M datasheet, CD74HCT238M pinout, CD74HCT238M application, or CD74HCT238M equivalent, this page provides verified functional behavior, SOIC-16 package details, output polarity confirmation (active-high Y0–Y7), thermal performance (RθJA = 73°C/W), and direct alternative options for system-level design continuity.
Technical Context
The CD74HCT238M implements a 3-input address decoder (A0–A2) with three independent strobe enables: G2 (standard active-high), G1 and G0 (both active-low). When any strobe is asserted, all eight outputs (Y0–Y7) are forced low - distinguishing it from the '138 family's active-low output behavior.
Its HCT logic family ensures TTL-compatible input thresholds (VIL ≤ 0.8 V, VIH ≥ 2.0 V) and CMOS-level output drive (±4 mA), enabling seamless interfacing with legacy LSTTL and modern mixed-voltage systems without level-shifting.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | HCT - TTL-compatible inputs, CMOS outputs, 4.5–5.5 V operation |
| Propagation Delay (tpd) | 14 ns typ. (address-to-output, VCC = 4.5 V, CL = 15 pF) - enables sub-70 MHz clocked decode timing |
| Output Drive | ±4 mA (IOH/IOL) - sufficient to directly drive 10 LSTTL loads or small LED indicators |
| Operating Temperature | -55°C to +125°C - qualified for extended industrial and aerospace environments |
| Power Dissipation Cap. | 67 pF (Cpd) - used to calculate dynamic power: Pdyn = Cpd × VCC² × fin |
| Input Leakage Current | ±1 µA max (VCC = 5.5 V) - negligible loading on upstream drivers or pull-up networks |
| Thermal Resistance | RθJA = 73°C/W (SOIC-16) - defines maximum junction rise above ambient at given power dissipation |
Pinout & Package
CD74HCT238M is supplied in a 16-pin SOIC (D) package with 9.90 mm × 3.90 mm body size, gull-wing leads, and RoHS-compliant NIPDAU/SN finish. Moisture sensitivity level is Level-1 (260°C peak reflow).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (A0) | Address Input | LSB of 3-bit binary address; determines decoded output selection |
| 2 (A1) | Address Input | Middle bit of address; combined with A0/A2 to select one of eight outputs |
| 3 (A2) | Address Input | MSB of address; completes 3-bit decode word |
| 4 (G0) | Enable Input | Active-low strobe; assertion forces all Y0–Y7 low regardless of address |
| 5 (G1) | Enable Input | Active-low strobe; second cascade control for hierarchical decoding |
| 6 (G2) | Enable Input | Active-high strobe; primary enable for demultiplexing mode |
| 7 (Y7) | Output | Active-high decoded output corresponding to A2A1A0 = 111 |
| 8 (GND) | Power | Ground reference for logic and supply return path |
| 9 (Y6) | Output | Active-high decoded output for A2A1A0 = 110 |
| 10 (Y5) | Output | Active-high decoded output for A2A1A0 = 101 |
| 11 (Y4) | Output | Active-high decoded output for A2A1A0 = 100 |
| 12 (Y3) | Output | Active-high decoded output for A2A1A0 = 011 |
| 13 (Y2) | Output | Active-high decoded output for A2A1A0 = 010 |
| 14 (Y1) | Output | Active-high decoded output for A2A1A0 = 001 |
| 15 (Y0) | Output | Active-high decoded output for A2A1A0 = 000 (LSB output) |
| 16 (VCC) | Power | +4.5 V to +5.5 V supply rail; requires local 0.1 µF bypass capacitor |
Key Features
| Feature | Design Value |
|---|---|
| Active-high output architecture | Y0–Y7 go high only when selected and all enables satisfied - simplifies interface to microcontroller GPIOs expecting active-high enable signals |
| Three independent enable inputs | G2 (active-high), G1/G0 (active-low) allow flexible hierarchical decoding across multiple CD74HCT238M devices without external logic |
| TTL-compatible input thresholds | VIL ≤ 0.8 V / VIH ≥ 2.0 V ensures reliable operation with 5 V LSTTL outputs without level shifters |
| Low dynamic power consumption | 67 pF Cpd and <160 µA ICC max reduce heat generation in dense logic arrays and battery-sensitive applications |
| Extended temperature qualification | -55°C to +125°C operation supports deployment in motor drives, avionics, and downhole instrumentation |
Applications
| Industrial PLC I/O Expansion | Automotive Body Control Module |
|---|---|
Use Scenario: Expanding discrete input/output points in programmable logic controllers using address-mapped peripheral chips. IC Role / Device Role / Timing Role: Address decoder selecting one of eight peripheral ICs (e.g., ADCs, DACs, GPIO expanders) via shared data bus. Use Value: Enables single microcontroller to manage up to 64 I/O lines using three address lines and three enables - reducing MCU pin count and PCB routing complexity. | Use Scenario: Controlling individual lighting zones (headlights, interior lamps, turn signals) from a central BCM microcontroller. IC Role / Device Role / Timing Role: Demultiplexer routing PWM or ON/OFF commands from MCU to dedicated lamp driver ICs. Use Value: Active-high outputs directly drive enable pins of high-side switches (e.g., TPS4H160-Q1), eliminating need for inverters in each channel path. |
| Test Equipment Signal Routing | Avionics Data Acquisition System |
Use Scenario: Selecting one of eight analog sensor inputs (thermocouples, strain gauges) for digitization in automated test equipment. IC Role / Device Role / Timing Role: Decoder enabling specific analog multiplexer channel while disabling others to prevent signal crosstalk. Use Value: 14 ns tpd ensures minimal latency between address change and valid analog channel selection - critical for high-throughput sampling. | Use Scenario: Distributing time-synchronized trigger pulses to eight separate flight data recorder modules during emergency events. IC Role / Device Role / Timing Role: Synchronous demultiplexer ensuring simultaneous activation of all eight recorder start inputs upon command. Use Value: Guaranteed -55°C to +125°C operation and 73°C/W thermal resistance support reliable pulse distribution in unpressurized avionics bays. |
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 |
|---|---|---|---|
| CD74HCT138M | Identical pinout and package, but outputs are active-low (Y0–Y7 low when selected) | Requires inverted logic in downstream circuitry or additional inverters for active-high load interfaces | Select CD74HCT138M only if existing design uses active-low enables or drives open-collector loads |
| SN74HCT238N | Same function and electrical specs, but in PDIP-16 package (25.4 mm × 6.35 mm); higher RθJA (67°C/W) | Suitable for prototyping or through-hole assembly; not recommended for high-density or thermally constrained PCBs | Choose SN74HCT238N for breadboarding or legacy through-hole production; CD74HCT238M preferred for volume SMT manufacturing |
Compared with CD74HCT138M and SN74HCT238N, the CD74HCT238M uniquely combines active-high output behavior with SOIC-16 thermal and space efficiency - making it optimal for surface-mount industrial controllers where output polarity and board area are jointly constrained.
Availability
CD74HCT238M is available at Aetrix Electronics and suitable for industrial automation, automotive electronics, and avionics applications requiring stable component supply, long-term lifecycle support, and guaranteed RoHS compliance.
Supply support for CD74HCT238M 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 connectivity solutions for industrial, automotive, and communications markets.
The CD74HCT238M belongs to TI's legacy high-speed CMOS logic family, engineered specifically for robust, low-power address decoding and signal routing in harsh-environment embedded systems.
FAQ
What is the output behavior of CD74HCT238M when all enable inputs are asserted?
When G2 is high and both G1 and G0 are low, the CD74HCT238M decodes the A2–A0 address and drives exactly one output (Y0–Y7) high; all others remain low. If any enable is deasserted (e.g., G2 low, or G1/G0 high), all eight outputs are forced low - confirming its active-high output architecture and explicit disable state.
Can CD74HCT238M operate reliably at 3.3 V supply voltage?
No. The CD74HCT238M is an HCT-family device specified only for 4.5 V to 5.5 V operation. At 3.3 V, input thresholds (VIL ≤ 0.8 V, VIH ≥ 2.0 V) may not be met, and output drive strength drops significantly. For 3.3 V systems, use CD74HC238M (HC family, 2–6 V) instead.
How does CD74HCT238M differ from CD74HCT138M in functional operation?
The CD74HCT238M and CD74HCT138M share identical pinout, enable structure, and timing, but differ fundamentally in output polarity: CD74HCT238M outputs go high when selected (active-high), while CD74HCT138M outputs go low (active-low). This dictates opposite logic interpretation in downstream circuits and eliminates need for external inverters in active-high load interfaces.
What is the maximum capacitive load CD74HCT238M can drive while maintaining specified propagation delay?
The CD74HCT238M's 14 ns typical propagation delay is characterized at CL = 15 pF. Driving loads >50 pF increases tpd nonlinearly; for CL = 50 pF, tpd rises to 35 ns (max) per datasheet Table 5.5. Maintain CL ≤ 30 pF for designs requiring <20 ns decode latency.
Is CD74HCT238M pin-compatible with SN74HCT238N?
Yes - CD74HCT238M (SOIC-16) and SN74HCT238N (PDIP-16) share identical pin numbering, signal mapping, and electrical specifications. However, their packages differ mechanically and thermally: SOIC offers better density and 73°C/W RθJA, while PDIP provides easier manual soldering and 67°C/W RθJA.
CD74HCT238M Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74HCT
- Package/Case:
- 16-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tube
- Product Status:
- Obsolete
- Type:
- Decoder/Demultiplexer
- Circuit:
- 1 x 3:8
- Independent Circuits:
- 1
- Current - Output High, Low:
- 4mA, 4mA
- Voltage Supply Source:
- Single Supply
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- -55°C ~ 125°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SOIC
CD74HCT238M FAQ
1.How can I place an order for CD74HCT238M through Aetrix?
Please submit a Request for Quotation (RFQ) for CD74HCT238M 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 CD74HCT238M reliable?
The price and inventory of CD74HCT238M are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for CD74HCT238M is usually 5 days.
3.What payment methods are accepted for CD74HCT238M?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for CD74HCT238M transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for CD74HCT238M?
CD74HCT238M orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your CD74HCT238M 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 CD74HCT238M?
For technical support, including CD74HCT238M datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your CD74HCT238M requirements.
6.How does Aetrix verify that CD74HCT238M is sourced from the original manufacturer or authorized distributors?
All CD74HCT238M 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 CD74HCT238M meets industry standards.
7.What is the process for return or replacement of CD74HCT238M?
All CD74HCT238M units undergo pre-shipment inspection (PSI). If there is an issue with CD74HCT238M, 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 CD74HCT238M part is unused and in its original packaging.
Return procedure for CD74HCT238M:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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