Texas Instruments CD54HC4538F3A

Overview

CD54HC4538F3A from Texas Instruments is a dual retriggerable/resettable monostable multivibrator in 16-lead CERDIP package, operating from 2V to 6V with -55°C to +125°C temperature range. It delivers precise output pulse widths (e.g., 0.63–0.81 ms with RX=10kΩ, CX=0.1µF), independent trigger/reset propagation delays (<75 ns at VCC=6V), and Schmitt-trigger inputs on A/B terminals for noise immunity in timing-critical industrial control systems.

For engineers reviewing the CD54HC4538F3A datasheet, CD54HC4538F3A pinout, CD54HC4538F3A application, or CD54HC4538F3A equivalent, key selection criteria include its wide operating temperature range, retriggerable edge-triggering capability (leading or trailing), buffered Q/Q outputs, and compatibility with external RC timing networks for adjustable pulse generation in aerospace and defense timing circuits.

Technical Context

The CD54HC4538F3A implements two independent monostable multivibrators with separate A (leading-edge) and B (trailing-edge) trigger inputs, each with dedicated R reset and RX/CX timing network connections. Its internal architecture uses CMOS logic with Schmitt-trigger inputs to ensure reliable edge detection despite slow-rising or noisy signals.

Propagation delay from A/B or R input to Q/Q output remains independent of RX and CX values, enabling stable timing across varying RC configurations. Retrigger time is also independent of CX, supporting robust operation in high-frequency pulse train environments where overlapping triggers occur.

Key Specifications

Pinout & Package

CD54HC4538F3A is housed in a 16-lead Ceramic Dual In-line Package (CERDIP), hermetically sealed for high-reliability operation in harsh environments. The package features through-hole leads with SNPB (tin-lead) finish and no moisture sensitivity rating (MSL N/A).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual monostable multivibrator applications.

Compared with CD74HC4538E and CD54HCT4538F3A, the CD54HC4538F3A uniquely combines military-grade temperature range, hermetic CERDIP reliability, and pure CMOS input thresholds - making it the only choice for high-integrity timing in space, aviation, and defense platforms where environmental resilience is non-negotiable.

Availability

CD54HC4538F3A is available at Aetrix Electronics and suitable for avionics watchdog timers, military radar pulse shaping, spacecraft power sequencing, and secure crypto module timing requiring stable component supply across extreme temperature and long-lifecycle programs.

Supply support for CD54HC4538F3A 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 high-reliability logic solutions for industrial, automotive, aerospace, and defense markets.

The CD54HC4538F3A belongs to TI's military-grade HC logic family, designed specifically for precision timing applications demanding extended temperature operation, radiation tolerance, and long-term reliability in mission-critical systems.

FAQ

What is the maximum recommended value for the external timing resistor RX in CD54HC4538F3A?

The CD54HC4538F3A datasheet specifies a minimum RX of 5 kΩ but does not define an absolute maximum. However, leakage current limitations and noise susceptibility guidelines indicate RX should remain ≤1 MΩ to avoid externally induced noise errors and ensure stable timing accuracy across the full –55°C to +125°C range. For optimal performance, TI recommends staying within 10 kΩ to 500 kΩ in most deployed CD54HC4538F3A designs.

Can CD54HC4538F3A operate reliably at 2.0V supply voltage?

Yes, CD54HC4538F3A is fully specified down to 2.0V supply voltage, with guaranteed propagation delays (≤375 ns), output drive (10 LSTTL loads), and Schmitt-trigger hysteresis (30% of VCC) across the full military temperature range. At 2V, input thresholds become VIH ≥1.5V and VIL ≤0.5V, enabling interoperability with low-voltage microcontrollers and battery-powered subsystems while maintaining timing integrity.

How does the retriggerable mode function differ from non-retriggerable mode in CD54HC4538F3A?

In retriggerable mode, each new trigger pulse (on A or B) extends the output pulse width by one full τ period - ideal for extending timeouts during ongoing activity. In non-retriggerable mode, the output pulse width is fixed from the first trigger, regardless of subsequent inputs - achieved by connecting Q to B (for A-triggered operation) or Q to A (for B-triggered operation). This distinction is implemented externally via PCB routing, not internal configuration.

Is CD54HC4538F3A pin-compatible with CD74HC4538E?

Yes, CD54HC4538F3A and CD74HC4538E share identical pin assignments, electrical functionality, and truth table behavior. Both follow the standard 16-pin DIP layout with matching terminal functions (e.g., Pin 1 = 1CX, Pin 3 = 1R, Pin 4 = 1A). The only differences are package construction (CERDIP vs. PDIP) and temperature rating (–55°C to +125°C vs. 0°C to +70°C), making them drop-in replacements where environmental requirements align.

What protection is required for CD54HC4538F3A when using large timing capacitors (≥0.5 µF)?

When CX ≥ 0.5 µF, rapid power-down events may cause stored energy to discharge into Pin 2 or 14, risking device damage. TI mandates either a 1A-rated protection diode (e.g., 1N5395) with separate ground return, or a 51 Ω current-limiting resistor in series with CX. The resistor method introduces minor pulse width reduction, requiring RX adjustment to restore target τ - documented in Figure 13 of the CD54HC4538F3A datasheet.