Texas Instruments CD74HC123M

Overview

CD74HC123M from Texas Instruments is a dual retriggerable monostable multivibrator with independent resets, designed for precise pulse generation and timing control in digital systems. It operates from 2V to 6V, supports edge-triggering on both A (trailing) and B (leading) inputs, features Schmitt-trigger inputs for noise immunity, and delivers buffered Q/Q̅ outputs. Its external RC timing network enables adjustable pulse widths down to ~40 µs (RX = 10 kΩ, CX = 10 nF at VCC = 5 V), making it suitable for debouncing, delay generation, and event synchronization in industrial control logic.

For engineers reviewing the CD74HC123M datasheet, CD74HC123M pinout, CD74HC123M application, or CD74HC123M equivalent, key selection considerations include its -55°C to +125°C operating range, SOIC-16 package thermal performance (θJA = 73°C/W), retriggerable behavior versus non-retriggerable alternatives, and compatibility with HC-level CMOS input thresholds (VIH = 3.15 V min at VCC = 4.5 V).

Technical Context

The CD74HC123M implements two independent monostable circuits, each with separate A/B trigger inputs, reset (R) input, and complementary Q/Q̅ outputs. Triggering is edge-sensitive: A responds to falling edges, B to rising edges - enabling flexible synchronization with asynchronous signals. The output pulse width tW = 0.45 × RX × CX (at VCC = 5 V) is externally programmable via resistor and capacitor values, with minimum RX = 5 kΩ and CX ≥ 0 pF.

Each monostable is retriggerable: a new valid trigger during an active output pulse extends the total duration. The reset input overrides timing and forces Q low (Q̅ high) asynchronously. Schmitt-trigger inputs on A, B, and R provide hysteresis (NIH/NIL = 30% of VCC), ensuring robust operation in noisy environments without requiring clean signal edges.

Key Specifications

Pinout & Package

CD74HC123M is housed in a 16-pin SOIC (Small Outline Integrated Circuit) package (Package Code: D), measuring 10.4 mm × 7.4 mm × 2.0 mm max height, with 1.27 mm lead pitch and gull-wing leads. Thermal resistance θJA = 73°C/W enables reliable operation at full temperature range with moderate PCB copper area.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC423M, the CD74HC123M adds retriggerability at identical package and voltage specs; versus SN74LVC1G123DBVR, it offers dual channels, true independent resets, and edge-select flexibility - justifying its use in robust industrial timing where predictability and configurability outweigh size savings.

Availability

CD74HC123M is available at Aetrix Electronics and suitable for industrial control panels, automotive body electronics, test equipment timing modules, and aerospace avionics requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HC123M 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

Texas Instruments is a global semiconductor leader delivering analog and embedded processing solutions, with over 90 years of innovation in precision timing, logic, and power management ICs.

The CD74HC123M belongs to TI's legacy HC-series high-speed CMOS logic family, engineered for low-power, wide-voltage-range timing applications in harsh environments where reliability and temperature resilience are critical.

FAQ

What is the minimum external capacitor value supported by the CD74HC123M?

The CD74HC123M supports CX = 0 pF as the theoretical minimum external capacitance. In practice, stray capacitance dominates below ~2 pF, so stable operation typically begins at CX ≥ 10 pF. The device's timing equation tW = 0.45 × RX × CX remains valid down to this limit, and the CD74HC123M datasheet explicitly confirms CX ≥ 0 pF with RX ≥ 5 kΩ for guaranteed functionality.

Can the CD74HC123M operate reliably at 2.5 V supply voltage?

Yes, the CD74HC123M is fully specified for operation from 2 V to 6 V, including 2.5 V. At VCC = 2.5 V, VIH = 1.5 V (min), VIL = 0.5 V (max), and propagation delays increase to ~300 ns (A/B/R to Q, CL = 50 pF). All DC and AC parameters remain guaranteed across this range, making the CD74HC123M suitable for mixed-voltage 2.5 V logic systems.

How does the CD74HC123M handle simultaneous triggers on both A and B inputs?

When both A (falling) and B (rising) inputs receive valid edges simultaneously, the CD74HC123M triggers on whichever edge meets setup/hold timing first - typically governed by tH = 9 ns (min) at VCC = 6 V. The resulting output pulse is identical regardless of which input initiates it; the CD74HC123M does not prioritize one input over the other, and both edges are functionally equivalent trigger sources per monostable channel.

Is the CD74HC123M pin-compatible with the CD74HCT123M?

Yes, the CD74HC123M and CD74HCT123M share identical SOIC-16 pinouts and package dimensions. However, they differ electrically: CD74HC123M operates from 2–6 V with CMOS input thresholds, while CD74HCT123M is 4.5–5.5 V only with TTL-compatible inputs (VIH = 2 V min, VIL = 0.8 V max). Interchangeability requires matching supply and driving logic families - the CD74HC123M is not a drop-in replacement in pure TTL systems.

What is the maximum recommended external resistor value for stable timing with the CD74HC123M?

The CD74HC123M datasheet does not specify a maximum RX, but practical limits arise from leakage current (II ≤ ±1 µA) and noise sensitivity. For reliable operation across -55°C to +125°C, TI recommends RX ≤ 1 MΩ when CX ≥ 100 pF. At higher values, timing accuracy degrades due to input bias current error; the CD74HC123M's internal design assumes RX in the 5 kΩ–100 kΩ range for optimal stability and repeatability.