STMicroelectronics M74HC123TTR

Overview

M74HC123TTR from STMicroelectronics is a dual retriggerable monostable multivibrator in TSSOP-16 package, implementing two independent edge-triggered one-shots with external RC timing control. It supports negative-edge (A) and positive-edge (B) triggering per channel, active-low/active-high complementary outputs (Q/Q̄), and direct reset (CLR) with Schmitt-trigger input. Pulse width ranges from 120 ns to 60 s at VCC = 4.5 V, with propagation delay tPD = 23 ns (typ.) at 6 V - used in precision timing, debounce, pulse shaping, and event synchronization in industrial control and instrumentation.

For engineers reviewing the M74HC123TTR datasheet, M74HC123TTR pinout, M74HC123TTR application, or M74HC123TTR equivalent, key selection considerations include retriggerable timing behavior, dual-channel independence, wide VCC range (2–6 V), symmetrical output drive (±4 mA), and compatibility with legacy 74-series logic interfaces.

Technical Context

The M74HC123TTR integrates two identical monostable circuits, each with separate A (negative-edge), B (positive-edge), and CLR (positive-edge) inputs, enabling flexible trigger source selection. Each channel features internal Schmitt-trigger inputs for noise immunity and independent Rx/Cx timing networks that determine output pulse width via tW(OUT) ≈ 0.45·Cx·Rx.

Its retriggerable architecture allows extension of the output pulse on subsequent valid triggers during the active period, while CLR forces immediate return to standby by rapidly charging Cx. The device operates across –55°C to +125°C with balanced tPLH/tPHL delays and supports slow input transitions (tr/tf up to 1 µs).

Key Specifications

Pinout & Package

TSSOP-16 package: 4.9 × 6.4 mm body, 0.65 mm pitch, 16-pin surface-mount, lead-free, RoHS-compliant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LV123A and 74HC4538, the M74HC123TTR uniquely guarantees retriggerable behavior across its full operating temperature range and supports wider VCC (up to 6 V), making it preferred for industrial systems requiring robust timing under voltage fluctuation and mechanical switch inputs.

Availability

M74HC123TTR is available at Aetrix Electronics and suitable for industrial automation, test equipment, and embedded control applications requiring stable component supply, extended temperature operation (–55°C to +125°C), and long-lifecycle availability.

Supply support for M74HC123TTR 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 M74HC123TTR belongs to ST's high-speed CMOS logic family, engineered for robust timing accuracy, low power consumption, and interoperability with legacy 74-series designs in harsh industrial environments.

FAQ

What is the minimum external capacitor value required for stable timing?

The datasheet specifies stable operation when Cx > 10 nF and Rx > 10 kΩ. Below 10 nF, timing accuracy degrades due to parasitic capacitance and comparator offset effects. For pulse widths under 1 µs, Cx = 100 pF is validated at VCC = 4.5 V with Rx = 10 kΩ, yielding tW(OUT) ≈ 1.2 µs - confirmed in AC characteristics Table on page 7.

Can M74HC123TTR operate reliably at VCC = 2.0 V?

Yes - the device is fully specified down to VCC = 2.0 V, with VIH = 1.5 V (min), VIL = 0.5 V (max), and tPLH/tPHL ≤ 315 ns (max) at TA = –55°C to +125°C. Output drive drops to ±20 µA at 2 V, sufficient for high-impedance CMOS loads but not for driving LEDs or TTL inputs directly.

How does the retriggering behavior affect minimum inter-pulse spacing?

Retriggering is effective only when the second trigger arrives during the capacitor discharge phase - i.e., before the R/C node voltage reaches VREFH. With Cx = 0.1 µF and Rx = 100 kΩ, minimum effective retrigger time (trr) is 1.4 µs at VCC = 4.5 V (page 7, AC table). Shorter intervals are ignored, preventing false pulse extension.

Is the M74HC123TTR pin-compatible with through-hole M74HC123B1R?

Yes - both share identical pin numbering and logic function mapping per channel. The TSSOP-16 (M74HC123TTR) and DIP-16 (M74HC123B1R) packages maintain 1:1 pin correspondence for all 16 terminals, including VCC, GND, A/B/CLR inputs, Q/Q̄ outputs, and RC nodes - verified in "PIN CONNECTION AND IEC LOGIC SYMBOLS" section (page 2).