STMicroelectronics HCF4538BEY

Overview

HCF4538BEY from STMicroelectronics is a dual retriggerable/resettable monostable multivibrator in 16-pin DIP package, operating from 3V to 20V supply. It delivers precision pulse widths (57 µs to 1.07 s) via external RX/CX networks, features independent trigger/reset propagation delays (100–600 ns), Schmitt-trigger inputs for edge-agnostic triggering, and buffered Q/Q̅ outputs-used in timing control, pulse shaping, and debounce circuits.

For engineers reviewing the HCF4538BEY datasheet, HCF4538BEY pinout, HCF4538BEY application, or HCF4538BEY equivalent, key selection criteria include retriggerable vs. non-retriggerable mode configuration, VDD-dependent noise margin (1–2.5 V), input leakage ≤100 nA at 18 V, output drive capability (±1.3–6.8 mA), and wide-temperature operation (–55°C to +125°C).

Technical Context

The HCF4538BEY integrates two independent CMOS monostables, each with separate +TR (rising-edge), –TR (falling-edge), and active-low RESET inputs. Timing is set externally via RX (≥4 kΩ) and CX (5 nF–100 µF), enabling pulse widths from microseconds to seconds without drift dependency on supply voltage.

Propagation delays for both trigger and reset paths are fully decoupled from RX/CX values and scale predictably with VDD: tPLH/tPHL ranges from 100 ns (15 V) to 600 ns (5 V). Input hysteresis ensures robust noise immunity across all VDD levels, and quiescent current is specified up to 20 V (≤3 mA max at 20 V, –55°C to +125°C).

Key Specifications

Pinout & Package

Package: 16-pin plastic DIP (0.300" width), JEDEC MS-001, body dimensions 20.0 × 8.5 mm.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD4538BE and 74HC4538N, the HCF4538BEY offers unique combination of 20 V operation, guaranteed Schmitt inputs, true retriggerability without external feedback, and ±1% dual-channel matching - making it the only option qualified for wide-supply, noise-prone, and precision dual-timing applications.

Availability

HCF4538BEY is available at Aetrix Electronics and suitable for industrial motor control, automotive body electronics, test equipment timing, and power supply sequencing requiring stable component supply across extended temperature and voltage ranges.

Supply support for HCF4538BEY 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, designing and manufacturing microcontrollers, power ICs, sensors, and analog/mixed-signal devices.

The HCF4538BEY belongs to ST's legacy HCMOS B-series logic family, engineered for robust, wide-supply operation in industrial and automotive timing applications where reliability across voltage and temperature extremes is essential.

FAQ

What is the minimum external resistor value for stable timing with HCF4538BEY?

The minimum external resistor (RX) value is 4 kΩ, as specified in the datasheet. Using lower values risks excessive current draw through the internal timing transistor, causing timing inaccuracy, increased power dissipation, and potential thermal instability-especially at high VDD or elevated temperatures.

Can HCF4538BEY operate in non-retriggerable mode without external components?

No. Non-retriggerable operation requires external feedback: connect Q to –TR when using +TR triggering, or Q to +TR when using –TR triggering. This cross-coupling disables retriggering by holding the unused trigger input inactive during the output pulse, enforcing single-shot behavior per initial trigger.

How does input leakage current affect timing accuracy at high RX values?

Input leakage (≤100 nA at 18 V) flows directly into the CX node, introducing timing error proportional to RX × II. At RX = 10 MΩ and II = 100 nA, this adds ~1 ms offset-significant for µs-range pulses. For sub-µs accuracy, keep RX ≤ 100 kΩ and use low-leakage capacitors (e.g., C0G ceramic) to minimize cumulative error.

Why are pins 1 and 15 electrically connected internally, and how should they be used?

Pins 1 and 15 are internally bonded to CX1 and CX2 respectively, and both are isolated nodes-not ground ties. They must connect only to their respective external timing capacitors. Connecting them together or to VSS/VDD violates the internal discharge path and prevents proper monostable operation; the datasheet explicitly warns against such misuse in Table 1 and functional descriptions.