Part A
74HC157D
東芝電晶體與存儲
- Lifecycle
- Active
- Stock
- 7197 件
- Package
- SOIC-16
- Series
- 邏輯-訊號開關、多工器、解碼器
Replacement verdict
Not a drop-in replacement
The 74HC123D and 74HC157D serve fundamentally different logic functions and cannot be used interchangeably in existing designs. The 74HC123D is a dual retriggerable monostable multivibrator for pulse generation, while the 74HC157D is a quad 2-input multiplexer for data selection. Substitution would require complete circuit redesign, including different pin assignments, signal routing, and timing considerations.
Different logic function
Different pinout
Different input configuration
Different output behavior
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HC123D | 74HC157D | Why it matters |
|---|---|---|---|
| Logic Function | Dual retriggerable monostable multivibrator with reset | Quad 2-input multiplexer | The core function differs completely; one generates timed pulses while the other selects between data inputs, so they are not functionally interchangeable. |
| Number of Channels | 2 | 4 | Channel count determines how many independent signals can be processed per package. |
| Output Type | Complementary (Q and Q-bar) pulse outputs | Non-inverting 3-state multiplexer outputs | Output configuration affects how the device interfaces with downstream logic and whether bus sharing is possible. |
| Propagation Delay (typical at 5 V) | Approximately 25 ns | Approximately 14 ns | Timing delay influences maximum operating frequency and signal integrity in synchronous designs. |
| Supply Voltage Range | 2 V to 6 V | 2 V to 6 V | Both support standard HC-family supply rails, allowing use in 3.3 V and 5 V systems. |
| Package | SO14 (SOIC-14) | SO16 (SOIC-16) | Different pin counts and footprints prevent direct drop-in replacement on the same PCB pad layout. |
| Pin Count | 14 | 16 | Pin count mismatch means the devices cannot share the same socket or footprint. |
| Operating Temperature Range | -40 °C to +125 °C | -40 °C to +125 °C | Both meet industrial temperature requirements, suitable for harsh environments. |
| Typical Application | Pulse generation, timing circuits, debouncing | Data selection, signal routing, bus multiplexing | Intended use cases differ, so substitution would require redesigning the surrounding circuit. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC157D | 74HC123D |
|---|---|---|
| Series | 74HC | 74HC |
| Part Status | Active | Active |
| Type | Multiplexer | - |
| Circuit | 4 x 2:1 | - |
| Independent Circuits | 1 | 2 |
| Current - Output High Low | 5.2mA, 5.2mA | 5.2mA, 5.2mA |
| Voltage Supply Source | Single Supply | - |
| Voltage - Supply | 2V ~ 6V | 2 V ~ 6 V |
| Operating Temperature | -40°C ~ 85°C | -40°C ~ 85°C |
| Mounting Type | Surface Mount | Surface Mount |
| Logic Type | - | Monostable |
| Schmitt Trigger Input | - | Yes |
| Propagation Delay | - | 40 ns |
Frequently asked questions
What are the primary functions of the 74HC123D and 74HC157D?
The 74HC123D is a dual retriggerable monostable multivibrator that generates a precise output pulse width determined by an external resistor and capacitor. The 74HC157D is a quad 2-input multiplexer that selects one of two 4-bit data sources based on a common select input.
Can the 74HC123D and 74HC157D be used interchangeably in a circuit design?
No. They perform fundamentally different logic functions. The 74HC123D is a timing device for pulse generation, while the 74HC157D is a data selection device. Substitution requires a complete redesign of the surrounding circuitry.
What are the key differences in pin count and package type between the 74HC123D and 74HC157D?
Both devices are typically offered in a 16-pin SOIC package (the "D" suffix in the part number). However, their pinouts are not compatible. The 74HC123D uses pins for external timing components (Rext/Cext), while the 74HC157D uses pins for data inputs, select, and enable functions.
Do the 74HC123D and 74HC157D operate at the same supply voltage and logic levels?
Yes. Both are 74HC series CMOS devices, typically specified for a supply voltage range of 2.0 V to 6.0 V, with standard CMOS logic thresholds. They are compatible with other 74HC-series logic in the same supply range.
Which device is suitable for debouncing a mechanical switch, the 74HC123D or the 74HC157D?
The 74HC123D is suitable for switch debouncing because its monostable output produces a single clean pulse of defined width for each input transition. The 74HC157D is a multiplexer and does not provide timing or pulse-shaping functions.
Can the 74HC157D be used to select between two clock signals, and does the 74HC123D offer a similar function?
The 74HC157D can select between two digital signal sources, including clock signals, based on its select input. The 74HC123D does not perform signal selection; it generates a pulse when triggered and is not intended for multiplexing clock or data lines.
Are the 74HC123D and 74HC157D available in the same temperature grade and RoHS status?
Both devices are commonly available in industrial temperature grade (-40 °C to +85 °C or +125 °C depending on manufacturer) and in RoHS-compliant packages. Specific ratings must be verified from the manufacturer datasheet for the exact orderable part number.