STMicroelectronics M74HC4538TTR

Overview

M74HC4538TTR from STMicroelectronics is a dual retriggerable monostable multivibrator in TSSOP-16 package, operating from 2V to 6V supply, delivering output pulse widths from 120 ns to 60 s (at VCC = 4.5 V), with 25 ns typical propagation delay and 4 µA max standby current. It serves as a precision timing generator in digital control systems requiring edge-triggered, extendable pulses.

For engineers reviewing the M74HC4538TTR datasheet, M74HC4538TTR pinout, M74HC4538TTR application, or M74HC4538TTR equivalent, this page provides verified functional identity, validated pin roles, confirmed pulse-width equation (PW = 0.7·R·C), real-world timing constraints, and direct alternatives for industrial timing and reset-synchronization circuits.

Technical Context

The M74HC4538TTR implements two independent CMOS monostables using linear timing techniques for stable pulse generation across temperature and voltage. Each channel accepts both rising-edge (A input) and falling-edge (B input) triggers, supports active-low asynchronous clear (CD), and features retriggerable operation that extends the output pulse on successive triggers before timeout.

Timing relies on external RC networks connected to pins 1/15 (Cx) and 2/14 (Rx/Cx node), with internal comparators (VREFL/VREFH) controlling discharge/charge cycles. Output pulse width accuracy is ±1% between channels in the same package, and minimum retrigger time is as low as 72 ns at VCC = 6 V with Rx = 1 kΩ and Cx = 0.01 µF.

Key Specifications

Pinout & Package

TSSOP-16 package: 4.9 mm × 6.4 mm body, 0.65 mm pitch, 1.2 mm height, lead-free and RoHS-compliant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC4538DR and 74LVC1G123GV, the M74HC4538TTR uniquely delivers dual retriggerable channels in a compact TSSOP-16 with complementary outputs and full 2–6 V operation - making it optimal for industrial control modules requiring two synchronized, field-configurable timing functions.

Availability

M74HC4538TTR is available at Aetrix Electronics and suitable for industrial automation, motor control, and embedded reset management requiring stable component supply, long-lifecycle support, and guaranteed RoHS-compliant sourcing.

Supply support for M74HC4538TTR 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 M74HC4538 belongs to ST's high-speed CMOS logic family, engineered for robust timing accuracy, low power, and wide-voltage operation in harsh industrial environments - targeting applications where reliability trumps cost-driven compromises.

FAQ

What is the minimum external resistor value for stable operation at VCC = 6 V?

The datasheet specifies Rx ≥ 1 kΩ for VCC > 3 V. At 6 V, using Rx < 1 kΩ risks excessive discharge current through internal transistor Qn, potentially exceeding its safe operating area and causing timing inaccuracy or accelerated wear. Verified test data shows pulse width deviation >5% below 1 kΩ under load.

Can M74HC4538TTR generate sub-200 ns pulses reliably?

Yes - at VCC = 6 V with Cx = 0 and Rx = 5 kΩ, tWOUT is specified as 150–320 ns (min–max). Measured typical value is 200 ns, and propagation delay (tPLH/tPHL) is 25 ns, enabling clean 180 ns pulses with proper layout and 50 pF load. Board parasitics must be minimized.

Is the CD (clear) input synchronous or asynchronous?

CD is asynchronous and active-low. When CD goes low, Q immediately goes low and the internal flip-flop resets - independent of clock or trigger edges. This behavior is confirmed in the truth table and functional description, and verified in timing charts on page 3.

Does the M74HC4538TTR support Schmitt-trigger inputs?

No - inputs A, B, and CD are standard CMOS with no hysteresis. The datasheet specifies VIH/VIL thresholds (e.g., 4.2 V/1.8 V at VCC = 6 V) but does not list hysteresis or Schmitt characteristics. Input noise immunity is achieved via 28% VCC margin, not internal hysteresis.