Texas Instruments SN74AHC123APWRG4

Overview

SN74AHC123APWRG4 from Texas Instruments is a dual retriggerable monostable multivibrator IC operating from 2 V to 5.5 V, featuring Schmitt-trigger inputs on A, B, and CLR for noise immunity, edge-triggered operation (rising or falling), and external RC-controlled pulse duration up to milliseconds. It delivers complementary Q and Q̅ outputs per channel and supports overriding clear for pulse termination - used in debounce circuits, timing delays, and pulse shaping in industrial control interfaces.

For engineers reviewing the SN74AHC123APWRG4 datasheet, SN74AHC123APWRG4 pinout, SN74AHC123APWRG4 application, or SN74AHC123APWRG4 equivalent, key selection criteria include its retriggerable monostable behavior, 16-pin TSSOP package with 5.00 mm × 6.4 mm footprint, guaranteed ±8 mA output drive at 5 V, and compatibility with slow-transition logic signals via integrated hysteresis.

Technical Context

The SN74AHC123APWRG4 implements two independent monostable multivibrators, each triggered by gated logic combinations of A (falling-edge active when B = H), B (rising-edge active when A = L), or CLR (rising-edge override). Pulse width is programmable via external R_ext and C_ext, with K-factor scaling dependent on capacitance value (K = 1.0 for C_ext ≥ 1000 pF).

Each channel provides both true and inverted outputs (Q and Q̅), supports retriggering during active output pulses, and features glitch-free power-up reset (Q low, Q̅ high). Input hysteresis ensures stable triggering even with input rise/fall times up to microseconds, and the overriding CLR input allows dynamic pulse shortening without requiring full cycle restart.

Key Specifications

Pinout & Package

TSSOP-16 (PW) package: 5.00 mm × 6.4 mm body size, 0.65 mm lead pitch, thin profile suitable for space-constrained PCBs.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LV123A and 74HC123, the SN74AHC123APWRG4 offers superior speed/power trade-off at 3.3 V, guaranteed operation down to −40 °C, and tighter pulse width stability (±0.5% vs ±2%), making it optimal for precision industrial timing where thermal drift and retrigger fidelity matter.

Availability

SN74AHC123APWRG4 is available at Aetrix Electronics and suitable for industrial control panels, test equipment timing modules, and embedded safety monitors requiring stable component supply, RoHS-compliant packaging, and long-term production continuity.

Supply support for SN74AHC123APWRG4 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 50 years of innovation in high-reliability timing and interface ICs.

The SN74AHC123A product line delivers retriggerable monostable functionality for hardware-based timing, debounce, and pulse shaping - designed specifically for industrial, automotive, and communications systems needing deterministic, low-jitter delay generation without software overhead.

FAQ

What is the minimum external timing capacitor value supported by SN74AHC123APWRG4?

The SN74AHC123APWRG4 supports external timing capacitors as low as 28 pF when used with R_ext = 2 kΩ, yielding nominal pulse widths of ~200 ns. For capacitors below 1000 pF, the K-factor must be interpolated from Figure 7-8 of the datasheet; values below 20 pF are not recommended due to parasitic sensitivity and reduced repeatability. The SN74AHC123APWRG4 datasheet specifies C_ext ≥ 28 pF for guaranteed performance across temperature and voltage.

Can SN74AHC123APWRG4 generate asymmetrical pulse widths on its two channels?

Yes - the SN74AHC123APWRG4 supports independent timing networks: pins 14–15 configure channel 1 (1Cext, 1Rext/Cext), while pins 6–7 configure channel 2 (2Cext, 2Rext/Cext). Using different R_ext or C_ext values per channel enables distinct pulse widths (e.g., 10 ms on channel 1, 100 µs on channel 2) without cross-talk. This capability is explicitly validated in the device functional modes table and timing diagrams.

Does SN74AHC123APWRG4 require external pull-up or pull-down resistors on unused inputs?

Yes - per TI's SCBA004 application report and the SN74AHC123APWRG4 datasheet Section 4.3, all unused A, B, and CLR inputs must be tied to either VCC or GND to prevent floating states that cause excessive ICC, erratic triggering, or increased EMI. Schmitt-trigger inputs do not eliminate this requirement; they only improve noise immunity for actively driven signals. Leaving inputs unconnected violates recommended operating conditions.

How does the overriding clear function interact with retriggering on SN74AHC123APWRG4?

The CLR input on SN74AHC123APWRG4 has priority over A/B retriggering: asserting CLR high during an active output pulse forces immediate termination (Q goes low, Q̅ goes high) regardless of ongoing retrigger events. Retriggering resumes only after CLR returns low and a new valid A/B edge occurs. This hierarchical control is confirmed in the function table (Table 6-1) and timing diagram Figure 4-11, ensuring deterministic timeout enforcement.

Is SN74AHC123APWRG4 compatible with 3.3 V-only systems without level shifters?

Yes - the SN74AHC123APWRG4 is fully specified for 3.3 V ± 0.3 V operation, with VIH = 2.1 V and VIL = 0.9 V at VCC = 3.3 V, providing 1.2 V noise margin for both logic high and low. Its 5.5 V absolute maximum rating also permits safe operation in mixed 3.3 V/5 V backplanes. All electrical characteristics, including t_PLH/t_PHL and output drive, are guaranteed across this range per Section 4.6–4.9 of the datasheet.