MM74HC123AMX Monostable Multivibrator Equivalent & Substitute Parts

Part Overview

The MM74HC123AMX is a monostable multivibrator logic IC manufactured by onsemi, housed in a 16-SOIC package with a 22 ns propagation delay. This part is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and procurement continuity. The 74HC123 series provides dual independent monostable circuits with Schmitt trigger inputs, suitable for timing and pulse generation applications across industrial and commercial electronics.

Key Parameters

Parameter	Value
Manufacturer Part Number	MM74HC123AMX
Manufacturer	onsemi
Base Product Number	74HC123
Logic Type	Monostable Multivibrator
Independent Circuits	2
Propagation Delay	22 ns
Schmitt Trigger Input	Yes
Current - Output High/Low	5.2 mA / 5.2 mA
Voltage - Supply	2 V ~ 6 V
Operating Temperature	-40°C ~ 85°C
Package / Case	16-SOIC (0.154", 3.90mm Width)
Mounting Type	Surface Mount
Product Status	Obsolete
Moisture Sensitivity Level (MSL)	1 (Unlimited)

Substitute Part Grouping Explanation

Substitution for the MM74HC123AMX is determined by the following critical parameters:

Primary Compatibility Criteria:

Logic type: Monostable multivibrator
Independent circuits: 2
Package / Case: 16-SOIC form factor (0.154", 3.90mm Width)
Voltage supply range: 2 V ~ 6 V (minimum overlap required)
Mounting type: Surface mount
Base product number: 74HC123 series

Secondary Compatibility Criteria:

Propagation delay: 22 ns (reference; faster alternatives acceptable for timing-critical applications)
Output current: 5.2 mA (reference; higher current ratings acceptable)
Operating temperature range: -40°C ~ 85°C (minimum; extended ranges acceptable)
Schmitt trigger input: Yes (preferred for noise immunity; alternatives without this feature remain functionally compatible)

Substitute parts must maintain electrical compatibility within the 2 V ~ 6 V supply range and preserve the dual-circuit monostable architecture. Package form factor compatibility is essential for PCB layout continuity.

Parameter Comparison

Part Number	Manufacturer	Series	Propagation Delay	Schmitt Trigger	Output Current (High/Low)	Voltage Supply	Temp Range	Package	Status
MM74HC123AMX	onsemi	74HC	22 ns	Yes	5.2 / 5.2 mA	2 V ~ 6 V	-40°C ~ 85°C	16-SOIC	Obsolete
74VHC123AMX	onsemi	74VHC	8.1 ns	Yes	8 / 8 mA	2 V ~ 5.5 V	-40°C ~ 85°C	16-SOIC	Active
74HC123D,653	Nexperia USA Inc.	74HC	65 ns	No	5.2 / 5.2 mA	2 V ~ 6 V	-40°C ~ 125°C	16-SOIC	Active
CD74HC123M96	Texas Instruments	74HC	25 ns	No	5.2 / 5.2 mA	2 V ~ 6 V	-55°C ~ 125°C	16-SOIC	Active
CD74HC123ME4	Texas Instruments	74HC	25 ns	No	5.2 / 5.2 mA	2 V ~ 6 V	-55°C ~ 125°C	16-SOIC	Discontinued at DiGi Electronics
CD74HC123MG4	Texas Instruments	74HC	25 ns	No	5.2 / 5.2 mA	2 V ~ 6 V	-55°C ~ 125°C	16-SOIC	Obsolete
CD74HC123MT	Texas Instruments	74HC	25 ns	No	5.2 / 5.2 mA	2 V ~ 6 V	-55°C ~ 125°C	16-SOIC	Discontinued at DiGi Electronics
CD74HC123NSR	Texas Instruments	74HC	25 ns	No	5.2 / 5.2 mA	2 V ~ 6 V	-55°C ~ 125°C	16-SO (0.209", 5.30mm)	Active

Engineering Selection Recommendations

Preferred Active Substitutes:

74VHC123AMX (onsemi) — Recommended for new designs and active procurement. This part maintains the 74HC123 base architecture with improved performance characteristics: 8.1 ns propagation delay (faster than the original 22 ns), Schmitt trigger inputs preserved, and higher output current (8 mA). Supply voltage range is 2 V ~ 5.5 V, which overlaps the original 2 V ~ 6 V specification. Product status is active with full manufacturer support.

CD74HC123M96 (Texas Instruments) — Suitable for direct substitution in existing designs. Propagation delay of 25 ns closely matches the original 22 ns specification. Output current and supply voltage are identical to the MM74HC123AMX. Operating temperature range extends to -55°C ~ 125°C, providing broader environmental coverage. Product status is active with established supply chain availability.

CD74HC123MT (Texas Instruments) — Alternative for tape & reel packaging requirements. Electrical specifications match CD74HC123M96. Product status is discontinued at DiGi Electronics; verify availability through alternative distributors before design commitment.

74HC123D,653 (Nexperia USA Inc.) — Acceptable for applications where propagation delay tolerance permits. The 65 ns delay is slower than the original 22 ns; this part is suitable only for non-timing-critical circuits. Schmitt trigger input is absent; applications requiring noise immunity should use alternatives with this feature. Product status is active. Operating temperature range extends to -40°C ~ 125°C.

CD74HC123NSR (Texas Instruments) — Functionally equivalent but with different package dimensions (16-SO, 0.209" width vs. 16-SOIC, 0.154" width). PCB layout modification is required. Product status is active. Use only when package footprint change is acceptable.

Parts to Avoid for New Designs:

CD74HC123ME4 and CD74HC123MG4 are discontinued or obsolete; procurement risk is high. Use only for legacy system maintenance where no alternatives are available.

Frequently Asked Questions (FAQ)

Q: Can I use 74VHC123AMX as a direct replacement for MM74HC123AMX?

A: Yes, with one supply voltage consideration. The 74VHC123AMX operates at 2 V ~ 5.5 V, while the original part supports 2 V ~ 6 V. If your circuit operates at 6 V, the 74VHC123AMX is not suitable. For 5.5 V and below, this is the preferred substitute due to active product status and improved propagation delay (8.1 ns vs. 22 ns).

Q: What is the difference between 16-SOIC and 16-SO packages?

A: Both are 16-pin surface-mount packages with similar pinouts. The primary difference is body width: 16-SOIC is 0.154" (3.90mm), while 16-SO is 0.209" (5.30mm). CD74HC123NSR uses the wider 16-SO package and requires PCB footprint modification. Verify your PCB layout before selecting this part.

Q: Why does 74HC123D,653 have a 65 ns propagation delay compared to 22 ns in the original?

A: Propagation delay varies by manufacturer process and design. The 65 ns specification from Nexperia is within the 74HC123 series tolerance but represents a slower device. This part is suitable only for applications where timing margins are not critical. For timing-sensitive circuits, use CD74HC123M96 (25 ns) or 74VHC123AMX (8.1 ns).

Q: Are all substitute parts RoHS compliant?

A: Yes. All active and recently discontinued parts listed carry RoHS3 compliance certification. The original MM74HC123AMX does not specify RoHS status; all substitutes meet modern environmental compliance requirements.

Q: Can I use CD74HC123MT if it is discontinued at DiGi Electronics?

A: Availability depends on alternative distributors and inventory levels. Verify current stock and lead times through secondary sources before committing to this part for production designs. For new designs, prioritize active parts: 74VHC123AMX or CD74HC123M96.

Q: Does the absence of Schmitt trigger input in some substitutes affect functionality?

A: Schmitt trigger input provides hysteresis for noise immunity on the input signal. Parts without this feature (74HC123D,653, CD74HC123M96, CD74HC123MT, CD74HC123NSR) remain functionally compatible but may require additional input filtering in noisy environments. For applications with clean input signals, this difference is not significant.

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