Texas Instruments CD74HC4538PWR

Overview

CD74HC4538PWR from Texas Instruments is a dual retriggerable/resettable monostable multivibrator in 16-pin TSSOP package, operating from 2V to 6V with ±25mA output drive, Schmitt-trigger inputs on A/B, and independent trigger/reset propagation delays unaffected by external timing components RX/CX. It delivers precise pulse widths (e.g., 0.63–0.81 ms with RX=10kΩ, CX=0.1µF) for timing-critical industrial control and instrumentation circuits.

For engineers reviewing the CD74HC4538PWR datasheet, CD74HC4538PWR pinout, CD74HC4538PWR application, or CD74HC4538PWR equivalent, key selection factors include its wide temperature range (–55°C to +125°C), retriggerable edge-triggering capability (leading or trailing), buffered Q/Q̅ outputs, and compatibility with both LSTTL and CMOS logic levels across supply voltages.

Technical Context

The CD74HC4538PWR implements two independent monostable sections, each with separate A (leading-edge) and B (trailing-edge) trigger inputs, dedicated R reset inputs, and external timing network pins (RX, CX, RXCX). Its internal Schmitt-trigger inputs enable noise-immune signal conditioning, while propagation delays (e.g., 43–75 ns at VCC=6V) remain stable regardless of RX/CX values.

Each section supports retriggerable operation-where successive triggers extend the output pulse-and non-retriggerable mode via feedback (Q→B for A-triggered, Q→A for B-triggered). The circuit self-resets on power-up, and unused inputs require proper termination (A→GND, B→VCC) to prevent metastability.

Key Specifications

Pinout & Package

CD74HC4538PWR uses a 16-pin Thin Shrink Small Outline Package (TSSOP) with 0.65 mm pitch, 5.1 mm × 4.5 mm body size, and 1.2 mm max height. Pin 1 is marked by a notch or dot in the top-left corner of the package.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC4538PWR, CD74HCT4538PWR offers stricter TTL input compatibility at the cost of supply flexibility, while SN74LVC1G123DCKR trades dual-channel programmability for speed and footprint reduction - making CD74HC4538PWR optimal for robust, field-deployable timing in variable-voltage industrial systems.

Availability

CD74HC4538PWR is available at Aetrix Electronics and suitable for industrial motor control, automotive sensor interface, test equipment pulse generation, and power supply sequencing requiring stable component supply across extended temperature ranges.

Supply support for CD74HC4538PWR 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 decades of heritage in high-reliability timing and interface solutions.

The CD74HC4538PWR belongs to TI's HC-series high-speed CMOS logic family, designed specifically for precision timing applications demanding wide voltage operation, noise immunity, and predictable pulse generation in harsh environments.

FAQ

What is the minimum external timing resistor value supported by CD74HC4538PWR?

The CD74HC4538PWR specifies a minimum external timing resistor (RX) of 5 kΩ. Using lower values risks exceeding the maximum allowable current (30 mA) into pins 2 or 14 (1RXCX/2RXCX), potentially causing timing inaccuracy or device stress. This limit ensures stable operation across the full –55°C to +125°C temperature range and maintains the specified pulse width accuracy of τ ≈ 0.7 × RX × CX.

Can CD74HC4538PWR operate reliably at 3.3V supply voltage?

Yes, CD74HC4538PWR operates reliably from 2V to 6V, including 3.3V nominal systems. At VCC = 3.3V, it maintains Schmitt-trigger input thresholds (VIH ≈ 2.3V, VIL ≈ 1.0V), 25mA output drive, and propagation delays within datasheet limits (e.g., tPLH ≤ 110 ns). Its HC logic family guarantees full functionality and noise immunity (NIL/NIH = 30% of VCC) at this voltage, making it ideal for mixed-signal embedded designs.

How does the retriggerable mode function in CD74HC4538PWR?

In retriggerable mode, CD74HC4538PWR extends the output pulse width by one full τ period upon each new trigger event - whether applied to A (rising edge) or B (falling edge) inputs. For example, if τ = 1 ms and triggers occur every 0.6 ms, the Q output remains high continuously until 1 ms after the final trigger. This behavior enables precise pulse stretching in applications like watchdog timeout extension or burst-mode signal conditioning without external logic.

What is the purpose of the RXCX pin in CD74HC4538PWR?

The RXCX pin (pins 2 and 14) serves as the combined node for the external timing resistor (RX) and capacitor (CX) in CD74HC4538PWR. It connects the junction of RX (to VCC) and CX (to GND), forming the RC network that sets the monostable pulse width τ ≈ 0.7 × RX × CX. Unlike conventional 555 timers, this pin interfaces directly with an internal comparator, enabling timing independence from supply voltage and temperature drift - a key advantage for precision industrial timing.

Is CD74HC4538PWR pin-compatible with CD74HCT4538PWR?

Yes, CD74HC4538PWR and CD74HCT4538PWR share identical 16-pin TSSOP packaging, pinout, and functional block diagram. They differ only in electrical characteristics: HC supports 2–6V operation with CMOS input thresholds, while HCT is optimized for 4.5–5.5V with TTL-compatible inputs. This allows direct substitution in 5V systems where input logic families match, though voltage range and noise margin requirements must be verified per application.