Texas Instruments CD74HC123EE4

Overview

CD74HC123EE4 from Texas Instruments is a dual retriggerable monostable multivibrator with independent resets, Schmitt-trigger inputs on both A and B trigger lines, buffered Q and Q̅ outputs, and external RC timing control (t_W = 0.45·R_XC_X at V_CC = 5V). It operates from 2V to 6V, supports -55°C to +125°C industrial/military temperature range, and delivers precise pulse-width generation for timing-critical digital systems.

For engineers reviewing the CD74HC123EE4 datasheet, CD74HC123EE4 pinout, CD74HC123EE4 application, or CD74HC123EE4 equivalent, this device is selected when dual independent one-shots with edge-selectable triggering (A = trailing-edge, B = leading-edge), overriding reset capability, and wide pulse-width adjustability (via external R/C) are required in legacy TTL- or CMOS-compatible logic designs.

Technical Context

The CD74HC123EE4 implements two fully independent monostable circuits, each with separate A (trailing-edge), B (leading-edge), and R (active-low reset) inputs. Triggering is enabled by Schmitt-trigger input thresholds (VIH = 1.5V min @ 2V, 3.15V min @ 4.5V; VIL = 0.5V max @ 2V, 1.35V max @ 4.5V), ensuring noise immunity and consistent edge detection regardless of input slew rate.

Each monostable is retriggerable: a new valid trigger during an active output pulse extends t_W, provided the minimum retrigger time (t_rT = 50 ns typ @ V_CC = 5V, R_X = 10 kΩ, C_X = 0) is met. Pulse termination is immediate upon LOW assertion of R, and unused inputs must be tied HIGH or LOW to prevent floating states.

Key Specifications

Pinout & Package

CD74HC123EE4 is supplied in a 16-pin plastic dual in-line package (PDIP-N), 0.300" wide, with standard through-hole mounting footprint and JEDEC MS-001 compliant dimensions (19.18 mm × 6.60 mm × 4.06 mm).

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC423E and CD74HCT123E, the CD74HC123EE4 uniquely combines wide-voltage operation (2–6V), retriggerability, and Schmitt-trigger inputs - making it the only option among the three for robust, flexible timing in variable-supply or noise-prone environments.

Availability

CD74HC123EE4 is available at Aetrix Electronics and suitable for industrial control panels, aerospace avionics interfaces, and military-grade test instrumentation requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for CD74HC123EE4 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 specializing in analog, embedded processing, and logic solutions, with over 90 years of innovation in high-reliability components.

The CD74HC123EE4 belongs to TI's legacy HC logic family, designed specifically for robust, low-power, wide-temperature digital timing applications in mission-critical systems where predictability and longevity are paramount.

FAQ

What is the minimum external timing capacitor value supported by the CD74HC123EE4?

The CD74HC123EE4 supports C_X = 0 pF as the minimum external timing capacitance. When C_X = 0, the output pulse width is determined solely by internal parasitic capacitance and R_X, yielding very short pulses (~tens of nanoseconds). For stable, predictable timing, TI recommends using ≥10 pF with appropriate R_X to achieve desired t_W per the formula t_W = 0.45·R_XC_X. The CD74HC123EE4 datasheet confirms C_X = 0 pF is valid and tested.

Can the CD74HC123EE4 operate reliably at 3.3V supply voltage?

Yes, the CD74HC123EE4 is fully specified for operation from 2V to 6V, including 3.3V nominal systems. At V_CC = 3.3V, input thresholds remain valid (VIH ≈ 2.1V min, VIL ≈ 1.0V max), propagation delay increases moderately (~100 ns max), and output drive strength remains sufficient for 10 LSTTL loads. All DC and switching parameters in the CD74HC123EE4 datasheet include 3.3V test conditions, confirming full functionality.

How does the reset function behave relative to the trigger inputs on the CD74HC123EE4?

The reset input (R) on the CD74HC123EE4 is asynchronous and overriding: asserting R LOW immediately forces Q = LOW and Q̅ = HIGH, terminating any active output pulse regardless of ongoing trigger activity on A or B. Reset takes priority over all trigger edges and retrigger events. Release of R (transition to HIGH) does not restart the monostable - a new valid edge on A or B is required to initiate the next pulse. This behavior is explicitly defined in the CD74HC123EE4 truth table and functional description.

Is the CD74HC123EE4 pinout identical to other members of the '123 family such as CD74HC123M or CD74HCT123E?

Yes, the CD74HC123EE4 shares identical pinout and pin functions with all 16-pin '123-family variants including CD74HC123M (SOIC), CD74HCT123E (PDIP), and CD74HC423E. This uniformity is confirmed in the TI datasheet's "Pinout" section and ordering table, which lists identical pin assignments across all PDIP, SOIC, SOP, and TSSOP packages. However, electrical characteristics (e.g., V_CC range, input thresholds) differ between HC and HCT types, so substitution requires verification of logic-level compatibility.

What is the maximum recommended value for the external timing resistor R_X in the CD74HC123EE4 circuit?

The CD74HC123EE4 datasheet does not specify an absolute maximum R_X, but practical limits arise from leakage current and noise sensitivity. TI recommends R_X ≤ 1 MΩ to maintain timing accuracy and avoid excessive sensitivity to stray capacitance or input leakage. At higher values, pulse width deviation increases due to internal input bias currents (±1 µA max), and noise coupling becomes more likely. For precision applications, R_X = 10 kΩ to 100 kΩ with C_X = 100 pF to 10 nF is the most stable operating region documented for the CD74HC123EE4.