Texas Instruments CD74HC4538M96

Overview

CD74HC4538M96 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 pins, buffered Q/Q̅ 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, debounce circuits, and programmable delay generators.

For engineers reviewing the CD74HC4538M96 datasheet, CD74HC4538M96 pinout, CD74HC4538M96 application, or CD74HC4538M96 equivalent, key selection considerations include its retriggerable mode operation, edge-selectable triggering (A = leading, B = trailing), wide 2V–6V supply range, ±1% pulse width matching between channels, and SOIC-16 package compatibility with industrial-grade thermal performance (θJA = 73°C/W).

Technical Context

The CD74HC4538M96 implements two independent monostable multivibrators, each with separate A (leading-edge) and B (trailing-edge) trigger inputs, R reset inputs, and Q/Q̅ complementary outputs. Timing is externally set by resistor RX and capacitor CX, with pulse width τ ≈ 0.7 × RX × CX - where RX ≥ 5 kΩ and CX ≥ 0 pF. Retrigger time is independent of CX, enabling stable multi-pulse extension without timing drift.

Its HC logic family ensures CMOS-level input thresholds (VIH = 1.5 V min at 2 V, 4.2 V min at 6 V), high noise immunity (NIL/NIH = 30% of VCC), and fanout of 10 LSTTL loads. Propagation delays from A/B or R to Q/Q̅ are fully decoupled from RX/CX values, guaranteeing consistent timing behavior across varying external component tolerances.

Key Specifications

Pinout & Package

CD74HC4538M96 is housed in a 16-pin SOIC (D) package (7.4 mm × 10.2 mm, 1.75 mm height), RoHS-compliant with NiPdAu lead finish and MSL Level-1 rating (unlimited floor life at ≤30°C/60% RH).

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC4538M96, CD74HCT4538M96 offers tighter input compatibility with older 5V logic but sacrifices supply flexibility, while SN74LV4538ADT reduces delay and size at the cost of pinout compatibility and external timing node independence - making CD74HC4538M96 optimal for robust, field-deployable timing where supply range and design stability are paramount.

Availability

CD74HC4538M96 is available at Aetrix Electronics and suitable for industrial automation, aerospace avionics, and test instrumentation requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HC4538M96 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 solutions, with over 90 years of innovation in high-reliability components.

The CD74HC4538M96 belongs to TI's High-Speed CMOS Logic portfolio, designed specifically for precision timing applications demanding retriggerable behavior, wide temperature operation, and noise-immune signal conditioning in mission-critical systems.

FAQ

What is the minimum external timing resistor value for stable operation of the CD74HC4538M96?

The CD74HC4538M96 requires RX ≥ 5 kΩ to ensure safe internal current limits (≤30 mA into pins 2/14) and prevent timing inaccuracy from leakage effects. Using lower values risks excessive current draw, thermal stress, and degraded pulse width accuracy - especially at high temperatures or with high-CX configurations.

Can the CD74HC4538M96 operate reliably at 3.3V supply voltage?

Yes, the CD74HC4538M96 is fully specified for 2V–6V operation, including 3.3V. At VCC = 3.3V, VIH = 2.31 V (min), VIL = 0.99 V (max), and propagation delays remain within datasheet limits (e.g., tPLH ≤ 100 ns). Its HC logic family ensures robust noise margins and fanout capability in modern 3.3V embedded systems.

How does the retriggerable mode function differ from non-retriggerable mode in the CD74HC4538M96?

In retriggerable mode, each new trigger pulse (on A or B) extends the output pulse by a full τ period - ideal for sustaining output during burst-mode events. In non-retriggerable mode (achieved by connecting Q to B for A-triggering), only the first trigger initiates the pulse; subsequent triggers are ignored until completion - useful for fixed-interval sampling or one-shot initialization sequences.

What is the purpose of the RXCX pin (pins 2 and 14) on the CD74HC4538M96?

Pins 2 (1RXCX) and 14 (2RXCX) serve as combined current-source outputs that charge the external timing capacitor CX. They integrate the internal constant-current generator with the external RC network - eliminating the need for separate current-setting resistors and enabling simplified, accurate pulse width calculation (τ ≈ 0.7 × RX × CX) without complex biasing circuitry.

Does the CD74HC4538M96 require external pull-up or pull-down resistors on unused inputs?

Yes - unused A inputs must be tied to GND and unused B inputs to VCC to prevent floating states that cause erratic triggering or increased ICC. Unused R inputs must also be pulled to VCC (inactive high) or actively driven low only when needed. Leaving any input unconnected violates the absolute maximum ratings and risks functional instability or ESD damage.