Texas Instruments CD74HC4538PWT

Overview

CD74HC4538PWT from Texas Instruments is a dual retriggerable/resettable monostable multivibrator IC used for precision timing in digital systems. It delivers independent trigger/reset propagation delays (e.g., 43–75 ns at VCC = 6 V), Schmitt-trigger inputs on A/B terminals, and buffered Q/Q̅ outputs. Its external RC timing network (RX ≥ 5 kΩ, CX ≥ 0 pF) enables adjustable pulse widths from microseconds to milliseconds - widely applied in pulse shaping, debouncing, and delay generation circuits.

For engineers reviewing the CD74HC4538PWT datasheet, CD74HC4538PWT pinout, CD74HC4538PWT application, or CD74HC4538PWT equivalent, key selection criteria include its -55°C to +125°C operating range, 2V–6V HC logic supply compatibility, dual-section independence, retriggerable edge-triggering capability (A = leading, B = trailing), and TSSOP-16 package suitability for space-constrained industrial control and test equipment designs.

Technical Context

The CD74HC4538PWT implements two independent monostable multivibrators with separate A (leading-edge), B (trailing-edge), R (reset), RX, and CX timing terminals per section. Each section features Schmitt-trigger inputs for noise immunity and buffered complementary outputs (Q/Q̅) with balanced transition times.

Propagation delays from A/B or R to Q/Q̅ are fully independent of external RX and CX values - enabling stable timing across wide pulse-width ranges. Retrigger time (≤175 ns at 5 V) and reset recovery time (5 ns) are specified under defined load and input slew conditions, supporting high-reliability timing in mixed-signal embedded systems.

Key Specifications

Pinout & Package

TSSOP-16 package (PW), 4.4 mm × 5.0 mm × 1.2 mm height, lead pitch 0.65 mm, RoHS-compliant NiPdAu finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC4538PWT, CD74HC4538M96 offers larger footprint and lower thermal resistance but identical timing behavior, while CD74HCT4538PWR trades supply flexibility for guaranteed TTL input thresholds - making the PWT optimal for modern mixed-voltage industrial designs requiring compact packaging and wide VCC range.

Availability

CD74HC4538PWT is available at Aetrix Electronics and suitable for industrial motor control, automotive sensor conditioning, test equipment signal generation, and medical instrumentation timing requiring stable component supply across extended temperature ranges.

Supply support for CD74HC4538PWT 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 logic solutions with emphasis on reliability, longevity, and industrial-grade qualification.

The CD74HC4538PWT belongs to TI's High-Speed CMOS Logic family, designed specifically for precision timing functions in harsh-environment applications where predictable pulse generation, wide temperature operation, and low power consumption are mandatory.

FAQ

What is the minimum external timing resistor value for CD74HC4538PWT?

The minimum external timing resistor (RX) for CD74HC4538PWT is 5 kΩ, as specified in the Absolute Maximum Ratings and Timing section. Using lower values risks exceeding the 30 mA maximum current into pins 2 or 14 (1RXCX nodes), potentially degrading timing accuracy or causing device stress. This value applies across the full -55°C to +125°C operating range and all valid VCC levels (2 V–6 V). The CD74HC4538PWT datasheet confirms this limit under Note 4 of the Operating Conditions table.

Can CD74HC4538PWT operate with CX = 0 pF?

Yes, CD74HC4538PWT supports CX = 0 pF (i.e., no external capacitor), enabling minimal-pulse-width operation determined solely by internal propagation delays and stray capacitance. The datasheet explicitly states "CX (Min) = 0 pF" in the Operating Conditions table and validates timing behavior down to 0 pF in Switching Specifications (CL = 50 pF, RX = 10 kΩ, CX = 0). However, practical minimum pulse width remains ~20 ns due to internal gate delays - confirmed by tPLH/tPHL measurements at VCC = 6 V.

How does the retriggerable mode function in CD74HC4538PWT?

In retriggerable mode, CD74HC4538PWT extends the output pulse width by one full timing period (τ = 0.7 × RX × CX) upon each new trigger event - even before the prior pulse completes. This behavior is inherent to the internal circuit architecture and requires no external feedback. The datasheet defines it as "an output pulse width which is extended one full time period (T) after application of the last trigger pulse" (Figure 2 notes). For CD74HC4538PWT, this occurs automatically when using A or B inputs without connecting Q to B or A - distinguishing it from non-retriggerable configurations.

What is the maximum recommended RX value for CD74HC4538PWT?

The CD74HC4538PWT datasheet does not specify a hard maximum RX value but warns that susceptibility to externally induced noise increases significantly when RX > 1 MΩ (Note 4, Operating Conditions). While functional operation may occur beyond this, timing accuracy degrades due to leakage currents from CX, the IC itself, and PCB surface resistance. TI recommends selecting RX and CX such that the maximum current into pins 2 or 14 remains ≤30 mA - a constraint that effectively caps RX at ~1 MΩ for typical CX values. This guidance applies identically to CD74HC4538PWT across all temperature and supply conditions.

Is CD74HC4538PWT pin-compatible with CD74HC4538PWR?

Yes, CD74HC4538PWT and CD74HC4538PWR share identical TSSOP-16 pinouts, terminal functions, and electrical specifications - differing only in packaging status (PWT is obsolete, PWR is active) and reel quantity (PWT: small-quantity reel of 250; PWR: large reel of 2000). Both use the PW package drawing, same pin numbering, and identical marking "HJ4538". No PCB layout changes are required when migrating from CD74HC4538PWT to CD74HC4538PWR, as confirmed in TI's Packaging Information and Package Outline documents.