Part A
74HC123D
NXP USA Inc.
- Lifecycle
- Active
- Stock
- 3320 PCS
- Package
- SOIC-16
- Series
- Lógica - Multivibradores
Replacement verdict
Not a drop-in replacement
The 74HC126D and 74HC123D are not functionally interchangeable despite sharing the same 74HC logic family and SOIC-14 package. The 74HC126D is a quad non-inverting 3-state buffer, while the 74HC123D is a dual retriggerable monostable multivibrator. Their internal architectures, pin functions, and logic behaviors are fundamentally different, so the 74HC123D cannot serve as a substitute for the 74HC126D in any existing design.
Different logic function
Different output type
Different pin function
Different timing behavior
Parts at a glance
Part B
74HC126D
Toshiba Semiconductor and Storage
- Lifecycle
- Active
- Stock
- 7257 PCS
- Package
- SOIC-14
- Series
- Lógica - Buffers, Drivers, Receivers, Transceivers
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HC126D | 74HC123D | Why it matters |
|---|---|---|---|
| Logic Function | Quad Buffer with 3-State Outputs | Dual Retriggerable Monostable Multivibrator | The core function determines whether the device buffers/isolates signals or generates timed pulses, making them non-interchangeable in most designs. |
| Number of Channels | 4 | 2 | Channel count affects how many independent signals can be handled per package. |
| Output Type | 3-State | Push-Pull (with complementary Q and Qbar) | 3-state outputs allow bus sharing, while push-pull outputs drive fixed logic levels; this impacts system architecture. |
| Control Input | Output Enable (active HIGH) | Trigger inputs (A active LOW, B active HIGH) and Reset | Different control schemes mean the devices respond to different signal conditions, affecting circuit design. |
| Propagation Delay (typical at 5V) | ~11 ns | ~25 ns (trigger to output) | Timing performance influences maximum operating frequency and signal integrity in high-speed applications. |
| Supply Voltage Range | 2 V to 6 V | 2 V to 6 V | Both support standard HC-family voltage ranges, allowing similar power supply compatibility. |
| Output Current (per channel) | ±6 mA (at 5V) | ±5.2 mA (at 5V) | Drive capability affects fan-out and ability to drive loads directly. |
| Package | SOIC-14 | SOIC-16 | Different pin counts and footprints prevent direct PCB drop-in replacement. |
| Operating Temperature Range | -40°C to +125°C | -40°C to +125°C | Both meet industrial temperature requirements, suitable for similar environments. |
| Typical Application | Bus buffering, signal isolation, line driving | Pulse generation, timing circuits, one-shot delays | Intended use cases differ fundamentally, so substitution requires redesign. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC123D | 74HC126D |
|---|---|---|
| Series | 74HC | 74HC |
| Part Status | Active | Active |
| Logic Type | Monostable | Buffer, Non-Inverting |
| Independent Circuits | 2 | - |
| Schmitt Trigger Input | Yes | - |
| Propagation Delay | 40 ns | - |
| Current - Output High Low | 5.2mA, 5.2mA | 7.8mA, 7.8mA |
| Voltage - Supply | 2 V ~ 6 V | 2V ~ 6V |
| Operating Temperature | -40°C ~ 85°C | -40°C ~ 125°C (TA) |
| Mounting Type | Surface Mount | Surface Mount |
| Number of Elements | - | 4 |
| Number of Bits per Element | - | 1 |
| Output Type | - | 3-State |
Frequently asked questions
What are the primary functional differences between the 74HC126D and the 74HC123D?
The 74HC126D is a quad non-inverting 3-state buffer with active-HIGH output enable pins, while the 74HC123D is a dual retriggerable monostable multivibrator with active-LOW and active-HIGH trigger inputs and complementary outputs.
Can the 74HC126D and 74HC123D be used interchangeably in a circuit design?
No. The 74HC126D provides buffered 3-state logic outputs controlled by enable pins, whereas the 74HC123D generates output pulses of a defined width determined by external RC components. Their pin functions, logic behavior, and application roles are fundamentally different.
Do the 74HC126D and 74HC123D share the same package and pinout?
Both devices are commonly offered in a 16-pin SOIC package (the D suffix), but their pinouts are not identical. The 74HC126D uses the 16 pins for four independent buffer channels with enable controls, while the 74HC123D uses the pins for two monostable multivibrator channels including timing, trigger, and reset inputs.
What are the typical supply voltage and logic family characteristics of both devices?
Both are members of the 74HC high-speed CMOS logic family and typically operate over a supply voltage range of 2.0 V to 6.0 V, with CMOS-compatible input thresholds and standard HC-family propagation delays and drive characteristics.
How does the output behavior of the 74HC126D differ from that of the 74HC123D?
The 74HC126D outputs follow the logic level present at each data input when the corresponding enable pin is HIGH, and enter a high-impedance state when the enable pin is LOW. The 74HC123D outputs produce a single pulse of determined width on each valid trigger event, with complementary Q and Q-bar outputs, and can be retriggered during the timing period.
Which device is suitable for bus buffering or tri-state data transmission?
The 74HC126D is intended for bus buffering and tri-state data transmission because its 3-state outputs allow multiple devices to share a common bus. The 74HC123D is not designed for bus buffering; it is used for pulse generation and timing functions.
Which device is suitable for pulse generation or timing applications?
The 74HC123D is designed for pulse generation and timing applications, with output pulse width set by external resistance and capacitance. The 74HC126D does not provide timing or pulse-width generation functions.
Are the 74HC126D and 74HC123D drop-in replacements for one another in existing PCB layouts?
No. Even if both are supplied in the same 16-pin SOIC package, their internal functions and pin assignments differ, so a direct drop-in replacement without schematic and layout changes is not valid. Each device must be used according to its own datasheet pinout and functional specification.