STMicroelectronics M74HC4538B1R

Overview

M74HC4538B1R from STMicroelectronics is a dual retriggerable monostable multivibrator in SO-16 package, operating from 2V to 6V supply, delivering pulse widths from 120 ns to 60 s (at VCC = 4.5 V), with tPD = 25 ns (typ.), symmetrical output drive (|IOH| = IOL = 4 mA min), and pin/function compatibility with standard 74-series 4538. It serves as a precision timing generator in digital control circuits requiring stable, externally adjustable one-shot pulses.

For engineers reviewing the M74HC4538B1R datasheet, M74HC4538B1R pinout, M74HC4538B1R application, or M74HC4538B1R equivalent, key selection criteria include retriggerability, external RC programmability (PW = 0.7·R·C), dual independent channels, low standby current (ICC = 4 µA max), and edge-triggered inputs with separate A (rising-edge) and B (falling-edge) logic.

Technical Context

The M74HC4538B1R implements two independent CMOS monostables using linear timing techniques for stable pulse width over temperature and supply voltage. Each channel features dual edge-triggered inputs (1A/1B, 2A/2B), an active-low direct reset (1CD/2CD), and complementary outputs (Q/Q̅), enabling flexible trigger polarity and synchronous clearing.

Timing relies on external RC networks connected to pins 1–2 (Channel 1) and 14–15 (Channel 2); discharge and charge cycles of Cx through Qn and internal reference comparators (VREFL/VREFH) determine pulse width, with tW(OUT) = 0.72·Cx·Rx confirmed across VCC = 2–6 V and TA = −55°C to +125°C.

Key Specifications

Pinout & Package

Package: SO-16 (Small Outline, 16-pin, 3.9 mm body width, 1.27 mm pitch), per mechanical data PO13H, compliant with JEDEC MS-012.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LV4538DR and 74HC4538D,653, the M74HC4538B1R uniquely supports 6 V operation and verified pulse widths up to 60 s, making it the only option among the three for high-voltage industrial timing and ultra-long-duration retriggerable events.

Availability

M74HC4538B1R is available at Aetrix Electronics and suitable for industrial automation, sensor signal conditioning, and motor control systems requiring stable component supply, long-term lifecycle support, and guaranteed SO-16 packaging consistency.

Supply support for M74HC4538B1R 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, Switzerland, designing and manufacturing analog, digital, and mixed-signal ICs for automotive, industrial, and consumer markets.

The M74HC4538B1R belongs to ST's high-speed CMOS logic family, engineered for robust timing accuracy, low-power operation, and interoperability with legacy 74-series designs in harsh industrial environments.

FAQ

What is the minimum external resistor value supported for stable pulse width generation?

The minimum external resistor Rx is 1 kΩ for VCC > 3 V and 5 kΩ for VCC < 3 V, as specified in Recommended Operating Conditions. Using lower values risks excessive discharge current, timing inaccuracy, and potential stress on internal transistors-verified by ST's characterization across −55°C to +125°C.

Can M74HC4538B1R operate reliably with ceramic capacitors down to 10 pF?

Yes-datasheet AC characteristics confirm stable tW(OUT) down to Cx = 0.01 µF (10 nF) with Rx = 10 kΩ, yielding ~70 µs pulses at VCC = 4.5 V. For sub-nanosecond pulses, layout parasitics dominate; use shortest possible traces and avoid vias near T1/T2 pins.

How does the retrigger time (trr) vary with external component values?

trr decreases with smaller Cx and Rx: e.g., trr(MIN.) = 72 ns at VCC = 6 V with Cx = 0.01 µF and Rx = 1 kΩ, versus 380 ns with Cx = 0.1 µF and Rx = 1 kΩ. This inverse relationship is derived from internal comparator response and RC discharge dynamics, not approximated.

Is the CD (clear) input asynchronous and level-sensitive?

Yes-the CD input is fully asynchronous and level-sensitive (active-low). When CD goes LOW, Q immediately goes LOW and internal timing state resets, overriding all ongoing trigger or retrigger activity-confirmed by truth table and functional description in sections 2 and 4 of the datasheet.