Part A
74HCT08D
Toshiba Semiconductor and Storage
- Lifecycle
- Active
- Stock
- 6154 PCS
- Package
- SOIC-14
- Series
- Logic - Gates and Inverters
Replacement verdict
Not a drop-in replacement
The 74HCT08D and 74HCT221D,118 are not functionally interchangeable despite sharing the 74HCT logic family and SO14 package. The 74HCT08D is a quad 2-input AND gate, while the 74HCT221D,118 is a dual monostable multivibrator with Schmitt-trigger inputs. Their logic functions, input/output characteristics, and timing behavior differ fundamentally, so the 74HCT221D,118 cannot directly replace the 74HCT08D in existing designs without significant circuit redesign.
Different logic function
Different output behavior
Different input type
Different timing characteristics
Parts at a glance
Part B
74HCT221D,118
Nexperia USA Inc.
- Lifecycle
- Active
- Stock
- 9432 PCS
- Package
- SOIC-16
- Series
- Logic - Multivibrators
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HCT08D | 74HCT221D,118 | Why it matters |
|---|---|---|---|
| Logic Function | Quad 2-input AND gate | Dual monostable multivibrator (one-shot) with reset | The logic function defines the fundamental behavior of the device; these two parts perform completely different operations and are not functionally interchangeable. |
| Number of Circuits | 4 | 2 | The number of independent channels determines how many signals can be processed simultaneously in a design. |
| Number of Inputs per Circuit | 2 | 2 (trigger inputs) plus reset | Input count affects how the device interfaces with surrounding logic and whether it can directly replace another part in a circuit. |
| Output Type | Push-pull (totem-pole) | Push-pull (totem-pole) | Output type determines drive capability and compatibility with other logic families and loads. |
| Supply Voltage Range | 4.5 V to 5.5 V | 4.5 V to 5.5 V | The supply voltage range must match the system rail to ensure correct logic levels and reliable operation. |
| Propagation Delay | Typically 9 ns at 5 V | Typically 25 ns at 5 V (trigger to output) | Propagation delay affects timing margins and maximum operating frequency in synchronous or timing-critical designs. |
| Output Current (High/Low) | ±4 mA | ±4 mA | Output current capability determines how many loads or what type of loads the device can drive directly. |
| Operating Temperature Range | -40 °C to +125 °C | -40 °C to +125 °C | The temperature range must cover the application environment to guarantee specified performance and reliability. |
| Package Type | SO14 (14-pin SOIC) | SO16 (16-pin SOIC) | Package type and pin count affect PCB footprint, layout, and whether a direct drop-in replacement is possible. |
| Pin Count | 14 | 16 | Different pin counts mean the devices are not pin-compatible and cannot be substituted without board redesign. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HCT08D | 74HCT221D,118 |
|---|---|---|
| Supplier | - | Nexperia USA Inc. |
| Series | 74HCT | 74HCT |
| Part Status | Obsolete | Active |
| Logic Type | AND Gate | Monostable |
| Independent Circuits | - | 2 |
| Schmitt Trigger Input | - | Yes |
| Propagation Delay | - | 31 ns |
| Current - Output High Low | 4mA, 4mA | 4mA, 4mA |
| Voltage - Supply | 4.5V ~ 5.5V | 4.5 V ~ 5.5 V |
| Operating Temperature | -40°C ~ 85°C | -40°C ~ 125°C |
| Mounting Type | Surface Mount | Surface Mount |
| Number of Circuits | 4 | - |
| Number of Inputs | 2 | - |
| Current - Quiescent (Max) | 1 µA | - |
| Logic Level - Low | 0.8V | - |
| Logic Level - High | 2V | - |
| Max Propagation Delay @ V Max CL | 18ns @ 5.5V, 50pF | - |
Frequently asked questions
What are the primary functional differences between the 74HCT08D and the 74HCT221D,118?
The 74HCT08D is a quad 2-input AND gate, providing four independent logic gates in a single package. The 74HCT221D,118 is a dual non-retriggerable monostable multivibrator (one-shot) with Schmitt-trigger inputs, used for pulse generation and timing applications. They serve fundamentally different logic and timing functions and are not functionally interchangeable.
Are the 74HCT08D and 74HCT221D,118 pin-compatible?
No. The 74HCT08D is typically supplied in a 14-pin SOIC package with a standard quad-gate pinout, while the 74HCT221D,118 is supplied in a 16-pin SOIC package with a different pin assignment for its dual monostable functions. The differing pin counts and functions prevent direct pin-to-pin substitution.
Do both devices operate from the same supply voltage range?
Yes. Both the 74HCT08D and the 74HCT221D,118 are HCT-family devices specified for a nominal 5 V supply, with a recommended operating supply voltage range of 4.5 V to 5.5 V per the respective manufacturer datasheets.
Can the 74HCT08D be used to replace the 74HCT221D,118 in a timing circuit?
No. The 74HCT08D is a combinational AND gate with no internal timing or pulse-stretching capability. The 74HCT221D,118 provides monostable pulse generation with externally programmable pulse width via resistor and capacitor components. Replacing the monostable with an AND gate would eliminate the timing function entirely.
What logic family and input threshold characteristics do these devices share?
Both are HCT (High-speed CMOS, TTL-compatible) devices. They feature TTL-compatible input thresholds when operated at 5 V, allowing direct interfacing with TTL logic levels while retaining CMOS output drive characteristics.
Which device is suitable for debouncing a mechanical switch signal?
The 74HCT221D,118 is suitable for switch debouncing because its monostable function can generate a clean, fixed-width output pulse from a noisy or bouncing input edge. The 74HCT08D, being a simple AND gate, does not provide debouncing or pulse conditioning on its own.
Are the output drive capabilities of the 74HCT08D and 74HCT221D,118 comparable?
Both devices are standard HCT-family parts and, per their manufacturer datasheets, provide symmetrical CMOS output drive suitable for driving standard logic loads. Detailed IOH and IOL limits should be verified against the specific manufacturer datasheet for each part, as drive strength can vary slightly between logic functions and suppliers.
Can both devices operate over the same industrial temperature range?
Both the 74HCT08D and the 74HCT221D,118 are typically specified for the standard industrial temperature range of -40 °C to +125 °C or -40 °C to +85 °C depending on the manufacturer and specific ordering variant. The exact temperature grade should be confirmed from the manufacturer datasheet for the specific part number ordered.