Texas Instruments CD74HC4538PW

Overview

CD74HC4538PW 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 CD74HC4538PW datasheet, CD74HC4538PW pinout, CD74HC4538PW application, or CD74HC4538PW equivalent, this page provides verified functional identity, validated TSSOP-16 pin mapping, confirmed -55°C to +125°C operation, true retriggerable/non-retriggerable mode behavior, and real-world design constraints including power-down protection requirements for CX ≥ 0.5µF.

Technical Context

The CD74HC4538PW implements two independent monostable sections, each with separate leading-edge (A) and trailing-edge (B) trigger inputs, dedicated reset (R), and buffered Q/Q̅ outputs. Its internal architecture uses precision RC timing where pulse width τ = 0.7 × RX × CX, with minimum RX = 5kΩ and CX ≥ 0 pF.

Propagation delays (tPLH/tPHL) range from 43 ns to 375 ns depending on VCC and load, while retrigger time trT is fixed at ≤175 ns (VCC = 5V), independent of CX value. Input rise/fall times are unrestricted for A/B at 4.5V/6V, enabling compatibility with slow or noisy edge sources.

Key Specifications

Pinout & Package

CD74HC4538PW is housed in a 16-pin Thin Shrink Small Outline Package (TSSOP), 4.4 mm × 5.0 mm footprint, 1.2 mm max height, with 0.65 mm lead pitch and exposed metal pad for thermal relief. Pin 1 marked via index area; JEDEC MO-153 compliant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC4538PW, CD74HC4538PWR offers identical functionality with assured long-term availability and tape-and-reel readiness, while SN74LV4538APWR trades Schmitt-trigger robustness for lower-voltage speed - making PWR the direct replacement and LV4538APWR a conditional alternative for 3.3V-clean-signal use cases.

Availability

CD74HC4538PW is available at Aetrix Electronics and suitable for industrial timer modules, automotive door lock controllers, test equipment pulse generators, and medical infusion pump safety monitors requiring stable component supply across extended temperature ranges.

Supply support for CD74HC4538PW 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 and embedded processing solutions, with over 90 years of innovation in precision timing, logic, and power management ICs.

The CD74HC4538 product line delivers dual retriggerable monostables optimized for high-reliability timing in industrial, automotive, and medical systems - designed to replace discrete RC-timing networks with predictable, temperature-stable pulse generation.

FAQ

What is the maximum external timing capacitor value supported by CD74HC4538PW?

The CD74HC4538PW datasheet does not specify an absolute maximum CX value, but notes that leakage in CX, the device, and PCB layout limits practical selection. For reliable operation, CX should be chosen so the current into pins 2 or 14 remains ≤30mA. Susceptibility to externally induced noise increases significantly when RX > 1MΩ, indirectly constraining usable CX at high RX values. Typical designs use CX from 100pF to 1µF.

Can CD74HC4538PW operate in non-retriggerable mode, and how is it configured?

Yes, CD74HC4538PW supports non-retriggerable mode. To configure monostable 1 for non-retriggerable operation using leading-edge triggering (A), connect Q1 output to B1 input. For trailing-edge triggering (B), connect Q1 to A1. This feedback forces the section to ignore subsequent triggers until the initial pulse completes, establishing a fixed one-shot period referenced from the first trigger edge.

What is the purpose of the Schmitt-trigger inputs on CD74HC4538PW A and B pins?

The Schmitt-trigger inputs on CD74HC4538PW A and B pins provide hysteresis (typically ~0.4V at VCC=5V), ensuring clean, bounce-free triggering from slow-rising or noisy signals. This eliminates multiple false triggers caused by signal ringing or gradual transitions - critical in industrial environments with long cables or electromagnetic interference, where standard CMOS inputs would misfire.

Is CD74HC4538PW pin-compatible with CD74HCT4538PW?

No, CD74HC4538PW is not pin-compatible with CD74HCT4538PW. While both share identical pinout and package (TSSOP-16), they differ electrically: HC types operate from 2V–6V with CMOS input thresholds, whereas HCT types require 4.5V–5.5V and feature TTL-compatible inputs (VIH=2V min, VIL=0.8V max). Interchanging them risks logic-level mismatch and undefined operation outside their respective VCC ranges.

Does CD74HC4538PW require external pull-up or pull-down resistors on unused inputs?

Yes, CD74HC4538PW requires proper termination of unused inputs. An unused A input must be tied to GND; an unused B input must be tied to VCC. Unused reset inputs and entire unused monostable sections must also be terminated - e.g., R tied to VCC to disable, or to GND to force reset - to prevent floating nodes from causing erratic triggering, increased current draw, or unintended output states during power-up or transient conditions.