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Texas Instruments CD74HCT4538E
- Part No.:
- CD74HCT4538E
- Manufacturer:
- Texas Instruments
- Category:
- Multivibrators
- Package:
- 16-DIP (0.300", 7.62mm)
- Datasheet:
-
CD74HCT4538E.pdf
- Description:
- IC MULTIVIBRATOR 23NS 16DIP
- Quantity:
- Payment:
- Shipping:
Inventory:289
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Product details
Overview
CD74HCT4538E from Texas Instruments is a dual retriggerable/resettable monostable multivibrator designed for precision timing in fixed-voltage systems. It delivers independent trigger/reset propagation delays (e.g., 55 ns max at 4.5 V), Schmitt-trigger inputs on A/B, buffered Q/Q outputs, and operates across -55°C to +125°C with 4.5–5.5 V supply. Used in pulse shaping, debounce, and timing control circuits where edge-selectable triggering and stable pulse width are critical.
For engineers reviewing the CD74HCT4538E datasheet, CD74HCT4538E pinout, CD74HCT4538E application, or CD74HCT4538E equivalent, key selection factors include its HCT-level LSTTL input compatibility (VIH ≥ 2 V, VIL ≤ 0.8 V), retrigger time independence from CX, dual-section reset isolation, and PDIP-16 package suitability for prototyping and high-reliability industrial timing.
Technical Context
The CD74HCT4538E implements two independent monostable sections, each with separate A (leading-edge) and B (trailing-edge) trigger inputs, dedicated R reset terminals, and external timing via RX and CX. Its internal architecture uses CMOS logic with TTL-compatible input thresholds and buffered complementary outputs, enabling direct interface with legacy LSTTL systems without level-shifting.
Propagation delay from A/B or R to Q/Q is independent of RX and CX values, ensuring consistent timing accuracy across wide pulse-width ranges (calculated as τ ≈ 0.7 × RX × CX). Retrigger capability allows pulse extension on successive triggers, while non-retriggerable mode is enabled by feedback wiring-Q to B for A-triggered operation or Q to A for B-triggered operation.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage | 4.5 V to 5.5 V - Ensures direct compatibility with standard 5 V LSTTL logic rails and eliminates need for voltage translation. |
| Input Compatibility | LSTTL-level: VIH ≥ 2 V (min), VIL ≤ 0.8 V (max) - Guarantees reliable recognition of legacy TTL signal levels without external biasing. |
| Propagation Delay | 55 ns max (A/B→Q, R→Q, CL = 50 pF, VCC = 4.5 V) - Enables precise sub-100 ns timing control in high-speed digital sequencing. |
| Operating Temperature | -55°C to +125°C - Supports deployment in extended industrial, aerospace, and automotive under-hood environments. |
| Output Drive | ±4 mA (standard loads), fanout = 10 LSTTL - Sufficient to drive multiple downstream TTL inputs without buffering. |
| Timing Accuracy | τ = 0.7 × RX × CX; RX ≥ 5 kΩ, CX ≥ 0 pF - Allows flexible pulse widths from microseconds to seconds using passive components. |
| Input Hysteresis | Schmitt-trigger on A/B inputs - Rejects noise on slow-rising/falling edges and prevents false triggering in noisy environments. |
Pinout & Package
CD74HCT4538E is housed in a 16-pin plastic dual in-line package (PDIP-N), with 0.3-inch body width and 0.1-inch lead pitch, optimized for through-hole prototyping and legacy PCB assembly.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 15 | 1CX / 2CX | External timing capacitor connection for Monostable 1 and 2 - Sets pulse width with associated RX; must be decoupled for stability. |
| 2, 14 | 1RXCX / 2RXCX | Combined timing resistor/capacitor node - Internal discharge path enables monostable timing; requires external RX to GND. |
| 3, 13 | 1R / 2R | Asynchronous reset input - Active-low; forces Q low and Q high regardless of trigger state; must be terminated if unused. |
| 4, 12 | 1A / 2A | Leading-edge trigger input - Schmitt-triggered; rising edge initiates output pulse; tie to GND if unused. |
| 5, 11 | 1B / 2B | Trailing-edge trigger input - Schmitt-triggered; falling edge initiates output pulse; tie to VCC if unused. |
| 6, 10 | 1Q / 2Q | Non-inverted output - Buffered, active-high pulse synchronized to trigger/reset; drives standard logic loads. |
| 7 | GND | Ground reference - Primary return path for all internal circuitry and external timing components. |
| 8, 9 | 1Q / 2Q | Inverted output - Complementary to Q; provides simultaneous active-low timing signal without external inverter. |
| 16 | VCC | Positive supply - 4.5–5.5 V only; bypass capacitor (0.1 µF) required near pin for noise immunity. |
Key Features
| Feature | Design Value |
|---|---|
| Retriggerable/Resettable Operation | Enables dynamic pulse extension during ongoing events (e.g., switch bounce suppression) or hard reset for deterministic state recovery. |
| Edge-Selectable Triggering | Independent A (rising) and B (falling) inputs per section allow precise synchronization to either transition of noisy or irregular signals. |
| Trigger/Reset Delay Independence | Timing delays remain constant regardless of RX/CX values - eliminates recalibration when adjusting pulse width. |
| Wide Pulse Width Range | Supports τ from ~1 µs to >1 s using standard resistors (5 kΩ–1 MΩ) and capacitors (0–100 µF), covering most discrete timing needs. |
| HCT Input Compatibility | Direct interface with 5 V TTL outputs avoids level shifters, reducing BOM count and layout complexity in mixed-logic systems. |
Applications
| Switch Debounce Circuit | Pulse Width Modulator Interface |
|---|---|
Use Scenario: Mechanical pushbutton or relay contact closure generates multiple transient bounces before settling. IC Role / Device Role / Timing Role: CD74HCT4538E acts as a hardware-based one-shot timer that produces a clean, glitch-free output pulse after the final bounce edge. Use Value: Eliminates need for software debouncing or RC+Schmitt circuits; ensures deterministic 5–50 ms stabilization window with no firmware overhead. | Use Scenario: Microcontroller GPIO generates variable-duty-cycle square wave to control analog subsystems (e.g., LED brightness, motor speed). IC Role / Device Role / Timing Role: CD74HCT4538E converts PWM edges into fixed-width pulses synchronized to rising/falling transitions. Use Value: Provides jitter-free, edge-aligned timing windows for analog sampling or gate drive enablement, independent of PWM frequency variation. |
| Dual-Channel Timing Generator | Legacy System Glue Logic |
Use Scenario: Industrial controller requires two independent, non-interfering timing intervals (e.g., sensor activation delay + data acquisition window). IC Role / Device Role / Timing Role: CD74HCT4538E provides two isolated monostable sections with separate resets, triggers, and timing networks. Use Value: Reduces component count vs. discrete 555-based solutions; guarantees matched temperature drift (<±1%) and identical propagation characteristics between channels. | Use Scenario: Retrofitting modern microcontrollers into aging equipment originally designed around 74LS logic families. IC Role / Device Role / Timing Role: CD74HCT4538E serves as drop-in compatible timing element replacing obsolete LS4538 or similar parts. Use Value: Maintains identical pinout, timing behavior, and drive strength while adding Schmitt inputs and wider temperature range (-55°C to +125°C). |
Equivalent & Alternatives
The following parts are listed as comparable options for similar dual monostable multivibrator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| CD74HC4538E | HC variant: 2–6 V supply, VIH/VIL referenced to VCC (not fixed TTL thresholds); higher noise immunity but no native LSTTL compatibility. | Requires level-shifting or redesign when interfacing with legacy 5 V TTL sources; better suited for mixed-voltage or battery-powered systems. | Select CD74HC4538E only if system operates outside 4.5–5.5 V or demands lower quiescent current (ICC < 160 µA). |
| SN74LS4538N | Obsolete bipolar TTL part: 4.75–5.25 V only, higher power (ICC ≈ 30 mA), slower propagation (100 ns typ), no Schmitt inputs. | Limited noise immunity and thermal range (-25°C to +70°C); unsuitable for high-reliability or extended-temperature deployments. | Use SN74LS4538N solely for exact form-fit-function replacement in legacy repairs where HCT compatibility is not required. |
Compared with CD74HC4538E and SN74LS4538N, CD74HCT4538E uniquely balances LSTTL input compatibility, wide temperature operation, low power, and Schmitt-trigger noise rejection - making it the optimal choice for upgrading or maintaining 5 V industrial control systems.
Availability
CD74HCT4538E is available at Aetrix Electronics and suitable for industrial control panels, aerospace avionics interfaces, and automotive engine management modules requiring stable component supply across extreme temperature cycles and long production lifecycles.
Supply support for CD74HCT4538E 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 ICs with over 90 years of innovation in high-reliability electronic components.
The CD74HCT4538E belongs to TI's High-Speed CMOS Logic family, engineered specifically for robust timing functions in mission-critical industrial, military, and automotive applications where precision, noise immunity, and extended temperature performance are mandatory.
FAQ
What is the minimum external timing resistor value supported by the CD74HCT4538E?
The CD74HCT4538E specifies a minimum external timing resistor (RX) of 5 kΩ. Using lower values risks excessive current into pins 2 and 14 (1RXCX/2RXCX), potentially exceeding the absolute maximum rating of ±30 mA and causing timing inaccuracy or device stress. Always verify RX ≥ 5 kΩ in designs using CD74HCT4538E.
Can the CD74HCT4538E operate with a 3.3 V supply?
No, the CD74HCT4538E is an HCT-type device rated strictly for 4.5 V to 5.5 V operation. At 3.3 V, input thresholds (VIH ≥ 2 V, VIL ≤ 0.8 V) become unreliable, propagation delays increase unpredictably, and output drive degrades. For 3.3 V systems, consider the HC-family CD74HC4538E instead - but note its VIH/VIL scale with VCC.
How does the retrigger time of the CD74HCT4538E depend on external components?
The retrigger time (trT) of the CD74HCT4538E is independent of RX and CX values - a key architectural feature confirmed in the datasheet (trT ≤ 175 ns typical at VCC = 5 V). This ensures consistent minimum interval between valid trigger pulses regardless of configured pulse width, simplifying timing-critical debounce or event-sampling designs using CD74HCT4538E.
What is the recommended termination for unused A and B inputs on the CD74HCT4538E?
Unused A inputs on the CD74HCT4538E must be tied to GND; unused B inputs must be tied to VCC. This prevents floating inputs from inducing noise-induced false triggering due to the Schmitt-trigger structure. Leaving them unconnected violates the functional requirements stated in the datasheet and may cause erratic output behavior in deployed CD74HCT4538E circuits.
Does the CD74HCT4538E support non-retriggerable one-shot operation?
Yes, the CD74HCT4538E supports non-retriggerable mode via external feedback: connect Q to B when using A for leading-edge triggering, or Q to A when using B for trailing-edge triggering. This configuration disables retriggering and locks the output pulse duration to the initial trigger - a documented function in the datasheet's functional terminal connections table for CD74HCT4538E.
CD74HCT4538E Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74HCT
- Package/Case:
- 16-DIP (0.300", 7.62mm)
- Packaging:
- Tube
- Product Status:
- Active
- Logic Type:
- Monostable
- Independent Circuits:
- 2
- Schmitt Trigger Input:
- Yes
- Propagation Delay:
- 23 ns
- Current - Output High, Low:
- 4mA, 4mA
- Voltage - Supply:
- 4.5 V ~ 5.5 V
- Operating Temperature:
- -55°C ~ 125°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 16-PDIP
CD74HCT4538E FAQ
1.How can I place an order for CD74HCT4538E through Aetrix?
Please submit a Request for Quotation (RFQ) for CD74HCT4538E 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 CD74HCT4538E reliable?
The price and inventory of CD74HCT4538E are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for CD74HCT4538E is usually 5 days.
3.What payment methods are accepted for CD74HCT4538E?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for CD74HCT4538E transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for CD74HCT4538E?
CD74HCT4538E orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your CD74HCT4538E 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 CD74HCT4538E?
For technical support, including CD74HCT4538E datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your CD74HCT4538E requirements.
6.How does Aetrix verify that CD74HCT4538E is sourced from the original manufacturer or authorized distributors?
All CD74HCT4538E 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 CD74HCT4538E meets industry standards.
7.What is the process for return or replacement of CD74HCT4538E?
All CD74HCT4538E units undergo pre-shipment inspection (PSI). If there is an issue with CD74HCT4538E, 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 CD74HCT4538E part is unused and in its original packaging.
Return procedure for CD74HCT4538E:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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