Texas Instruments CD74HC4538PWG4

Overview

CD74HC4538PWG4 from Texas Instruments is a dual retriggerable/resettable monostable multivibrator used for precision timing in digital systems. It delivers independent trigger/reset propagation delays (e.g., 43 ns max at 6 V), Schmitt-trigger inputs on A/B, buffered Q/Q outputs, and supports output pulse widths from microseconds to milliseconds via external RX/CX components. It operates across -55°C to +125°C and is commonly deployed in pulse shaping, debouncing, and delay generation circuits.

For engineers reviewing the CD74HC4538PWG4 datasheet, CD74HC4538PWG4 pinout, CD74HC4538PWG4 application, or CD74HC4538PWG4 equivalent, key selection criteria include its retriggerable mode operation, edge-selectable triggering (A = leading, B = trailing), wide 2–6 V supply range, ±1% pulse width matching between sections, and TSSOP-16 packaging for high-density PCB layouts.

Technical Context

The CD74HC4538PWG4 implements two independent monostable multivibrators with separate A (leading-edge) and B (trailing-edge) trigger inputs, each with dedicated R reset terminals. Its timing is governed by external RX resistors and CX capacitors, where pulse width τ ≈ 0.7 × RX × CX - with RX ≥ 5 kΩ and CX ≥ 0 pF - and retrigger time is independent of CX value.

Propagation delays from A/B or R to Q/Q are fully independent of RX and CX values, enabling stable timing across varying component tolerances. The device uses HC-series CMOS logic, delivering high noise immunity (NIL/NIH = 30% of VCC at 5 V), fanout of 10 LSTTL loads, and low quiescent current (≤160 µA over full temperature range).

Key Specifications

Pinout & Package

TSSOP-16 package (PW), 4.4 mm × 5.0 mm body, 0.65 mm pitch, 1.2 mm max height, RoHS-compliant NIPDAU lead finish, MSL Level-1 (260°C peak reflow).

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC4538PWR, CD74HC4538PWG4 offers identical timing, drive, and thermal performance but may differ in reel packaging documentation; versus SN74LV4538APWR, it trades speed for noise immunity and supply flexibility - making it preferable for industrial interfaces with marginal signal integrity.

Availability

CD74HC4538PWG4 is available at Aetrix Electronics and suitable for industrial control systems, automotive body electronics, and test equipment requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for CD74HC4538PWG4 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 CD74HC4538PWG4 belongs to TI's HC logic family - designed for precision, low-power, wide-voltage digital timing applications where noise immunity, thermal stability, and predictable monostable behavior are critical.

FAQ

What is the minimum external timing resistor value supported by CD74HC4538PWG4?

The CD74HC4538PWG4 specifies a minimum external timing resistor (RX) of 5 kΩ. Using lower values risks exceeding the 30 mA maximum current into pins 2 or 14 (1RXCX/2RXCX), potentially damaging the internal discharge transistor or degrading timing accuracy. At VCC = 6 V, 5 kΩ yields ~1.2 mA bias - well within safe limits while ensuring stable monostable operation.

Can CD74HC4538PWG4 operate in non-retriggerable mode, and how is it configured?

Yes, CD74HC4538PWG4 supports non-retriggerable mode. To configure MONO1 this way, connect its Q output to the B input (trailing-edge trigger) when using A for leading-edge triggering - or connect Q to A when using B. This feedback locks the output pulse duration to the initial trigger, preventing extension by subsequent edges. The same applies independently to MONO2.

Does CD74HC4538PWG4 require external pull-up or pull-down resistors on unused A/B inputs?

Yes. Unused A inputs must be tied to GND; unused B inputs must be tied to VCC. This prevents floating inputs from inducing unintended triggering due to noise or leakage. The datasheet explicitly states this requirement - failure to terminate unused A/B pins may cause erratic output behavior or increased ICC current, especially over temperature.

What is the maximum recommended value for the external timing capacitor CX in CD74HC4538PWG4?

The CD74HC4538PWG4 does not specify an absolute maximum CX value, but practical limits arise from leakage and board parasitics. For stable operation, TI recommends keeping CX ≤ 10 µF and using low-leakage types (e.g., X7R ceramic or polypropylene film). Above 0.5 µF, rapid power-down protection (e.g., 1N5395 diode or 51 Ω series resistor) is required to prevent reverse current damage to pins 2/14 during supply collapse.

How does the Schmitt-trigger input on CD74HC4538PWG4 improve system reliability?

The Schmitt-trigger inputs on A and B pins of CD74HC4538PWG4 provide hysteresis (typically ~0.8 V at VCC = 5 V), meaning the rising-edge threshold (~3.15 V) differs from the falling-edge threshold (~1.35 V). This prevents multiple triggering from slow-rising or noisy signals - such as mechanical switch bounce or EMI-coupled transients - ensuring one clean output pulse per valid edge transition, which is critical in industrial and automotive environments.