NXP Semiconductors 74HC4538N,652

Overview

74HC4538N,652 from Nexperia is a dual retriggerable precision monostable multivibrator in 16-lead DIP package, providing two independent timing channels with ±0.2% pulse width stability over temperature. Each channel accepts rising- or falling-edge triggers via dedicated A/B inputs, features active-low direct reset (nCD), and generates complementary outputs (nQ/nQ) with pulse width defined by external REXT and CEXT components. It operates across 2.0–6.0 V supply and supports industrial temperature range (−40 °C to +125 °C), commonly used in digital timing control, debounce circuits, and pulse shaping in instrumentation.

For engineers reviewing the 74HC4538N,652 datasheet, 74HC4538N,652 pinout, 74HC4538N,652 application, or 74HC4538N,652 equivalent, key selection considerations include its retriggerable behavior, Schmitt-trigger input tolerance for slow edges, precise 0.7 × REXT × CEXT timing equation, and compatibility with legacy 74HC logic families in through-hole designs.

Technical Context

The 74HC4538N,652 implements two independent monostable circuits using linear CMOS design techniques to guarantee accurate output pulse width control. Each multivibrator uses external REXT and CEXT components connected at pins nREXT/CEXT and nCEXT to set timing-pulse width TW = 0.7 × REXT × CEXT-with typical variation of only ±0.2% over −40 °C to +125 °C.

Triggering is edge-selective: nA responds to HIGH-to-LOW transitions, nB to LOW-to-HIGH transitions, and both support retriggering during an active output pulse. The nCD input provides asynchronous, active-low reset that terminates the output pulse immediately, while Schmitt-trigger action on all inputs ensures robust operation with slow-rising or slow-falling signals.

Key Specifications

Pinout & Package

74HC4538N,652 is supplied in a 16-lead plastic dual in-line package (DIP), designated SOT38-4 in Nexperia documentation. This through-hole package has 0.3-inch body width, 0.1-inch lead pitch, and is compatible with standard DIP sockets and wave-solder processes.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74HC4538D,118 and CD74HC4538E, the 74HC4538N,652 offers mechanical robustness and ease of hand-soldering via DIP packaging, while retaining identical timing precision and retriggerable functionality-making it optimal for lab validation, repair, and low-volume industrial controls.

Availability

74HC4538N,652 is available at Aetrix Electronics and suitable for industrial control panels, test equipment interfaces, and legacy system upgrades requiring stable component supply with long-term DIP package availability.

Supply support for 74HC4538N,652 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

Nexperia is a global semiconductor expert focused on essential efficiency technologies, delivering high-performance logic, analog, and discrete components with emphasis on reliability and manufacturability.

The 74HC4538 belongs to Nexperia's 74HC logic family-designed for low-power, high-noise-immunity digital timing and control in industrial, automotive, and consumer applications where precision and robustness are critical.

FAQ

What is the exact pulse width formula for 74HC4538N,652?

The output pulse width (TW) of the 74HC4538N,652 is precisely calculated as TW = 0.7 × REXT × CEXT, where REXT is the external timing resistor connected between nREXT/CEXT and VCC, and CEXT is the external timing capacitor connected between nCEXT and GND. This linear relationship holds across the full operating temperature and supply voltage ranges specified in the datasheet, with ±0.2% typical variation over −40 °C to +125 °C.

Can 74HC4538N,652 be triggered by both rising and falling edges simultaneously?

No-74HC4538N,652 does not support simultaneous rising/falling edge triggering on the same channel. Each monostable has dedicated inputs: nA triggers on HIGH-to-LOW (falling) edges, and nB triggers on LOW-to-HIGH (rising) edges. Both can be used independently, but only one edge type per input; concurrent assertion of both nA and nB does not produce combined or dual-edge behavior-it follows the first valid edge detected.

Does 74HC4538N,652 support retriggering during an active output pulse?

Yes-74HC4538N,652 is explicitly designed as a retriggerable monostable. When a new trigger (on nA or nB) occurs during an active output pulse, the timer resets and extends the output pulse width from that point onward. This behavior enables variable-width pulse generation from fixed-frequency inputs and is confirmed in the functional description and timing diagrams of the Nexperia datasheet Rev. 7.

What is the maximum recommended value for REXT in 74HC4538N,652?

The datasheet specifies REXT values up to 1 MΩ at VCC = 5.0 V. For reliable operation, REXT should remain within 2 kΩ to 1 MΩ per channel. Values below 2 kΩ risk excessive current draw and timing inaccuracies; values above 1 MΩ increase sensitivity to leakage and noise. At VCC = 2.0 V, minimum REXT is 10 kΩ-always pair REXT with CEXT to keep TW within practical limits and avoid timing drift due to capacitor ESR or dielectric absorption.

Is 74HC4538N,652 pin-compatible with older 74LS4538 or 74HC123 devices?

No-74HC4538N,652 is not pin-compatible with 74LS4538 or 74HC123. While all are dual monostables, their pin assignments differ significantly: 74HC4538N,652 uses separate nA/nB trigger inputs and nCD reset per channel, whereas 74HC123 has common reset and different timing pin topology (R/C on same pin). Substitution requires PCB layout changes and logic-level validation; the 74HC4538N,652 offers superior retriggering and precision but demands dedicated pin mapping.