Part A
74VHC244FT
東芝電晶體與存儲
- Lifecycle
- Active
- Stock
- 2156 件
- Package
- TSSOP-20
- Series
- 邏輯-緩衝器、驅動器、接收器、收發器
Replacement verdict
Not a drop-in replacement
The 74VHC244FT and 74VHCT74ATTR are functionally incompatible devices that cannot serve as substitutes for one another. The 74VHC244FT is an octal non-inverting buffer/line driver with 3-state outputs, while the 74VHCT74ATTR is a dual D-type flip-flop with preset and clear. Their differing logic functions, channel configurations, pin assignments, and package footprints make direct replacement impossible without substantial circuit redesign.
Different logic function
Different channel count
Different pin configuration
Different package footprint
Parts at a glance
Part B
74VHCT74ATTR
意法半導體
- Lifecycle
- Active
- Stock
- 2414 件
- Series
- 邏輯-觸發器
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74VHC244FT | 74VHCT74ATTR | Why it matters |
|---|---|---|---|
| Logic Function | Octal Buffer/Line Driver (3-state) | Dual D-Type Flip-Flop | These devices perform completely different logic functions, so they are not functionally interchangeable in a circuit. |
| Logic Family | VHC (Very High Speed CMOS) | VHCT (Very High Speed CMOS with TTL-compatible inputs) | VHCT inputs are TTL-voltage compatible, while VHC inputs are CMOS-level; this affects interfacing with other logic families. |
| Number of Channels | 8 (octal) | 2 (dual) | Channel count determines how many signals the device can process simultaneously. |
| Output Type | 3-state (tri-state) buffer | Standard push-pull (flip-flop outputs) | Tri-state outputs allow bus sharing, whereas standard outputs cannot be tied together without contention. |
| Supply Voltage Range | 2.0 V to 5.5 V | 4.5 V to 5.5 V | The narrower supply range of the VHCT device limits its use in low-voltage systems. |
| Propagation Delay (typical) | ~3.5 ns at 5 V | ~5.0 ns at 5 V | Propagation delay affects maximum operating frequency and timing margins in synchronous designs. |
| Input Type | CMOS-level inputs | TTL-compatible inputs | TTL-compatible inputs allow direct interfacing with TTL logic without level shifting. |
| Package | TSSOP-20 | TSSOP-14 | Different pin counts and footprints prevent direct drop-in replacement on the same PCB pad layout. |
| Operating Temperature Range | -40 °C to +85 °C | -40 °C to +85 °C | Both devices share the same industrial temperature range, suitable for similar environments. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74VHC244FT | 74VHCT74ATTR |
|---|---|---|
| Supplier | - | STMicroelectronics |
| Series | 74VHC | 74VHCT |
| Part Status | Active | Obsolete |
| Function | - | Set(Preset) and Reset |
| Type | - | D-Type |
| Output Type | 3-State | Complementary |
| Number of Elements | 2 | 2 |
| Number of Bits per Element | 4 | 1 |
| Clock Frequency | - | 140 MHz |
| Max Propagation Delay @ V Max CL | - | 8.8ns @ 5V, 50pF |
| Trigger Type | - | Positive Edge |
| Current - Output High Low | 8mA, 8mA | 8mA, 8mA |
| Voltage - Supply | 2V ~ 5.5V | 4.5V ~ 5.5V |
| Current - Quiescent (Iq) | - | 2 µA |
| Input Capacitance | - | 6 pF |
| Operating Temperature | -40°C ~ 125°C (TA) | -55°C ~ 125°C (TA) |
| Mounting Type | Surface Mount | Surface Mount |
| Logic Type | Buffer, Non-Inverting | - |
Frequently asked questions
What are the primary functional differences between the 74VHC244FT and the 74VHCT74ATTR?
The 74VHC244FT is an octal non-inverting buffer/line driver with 3-state outputs, while the 74VHCT74ATTR is a dual D-type positive-edge-triggered flip-flop with preset and clear. They serve entirely different logic functions and are not functionally equivalent.
Are the 74VHC244FT and 74VHCT74ATTR pin-to-pin compatible?
No. The 74VHC244FT is typically supplied in a TSSOP-20 package with 20 pins, while the 74VHCT74ATTR is supplied in a TSSOP-14 package with 14 pins. The pin counts, pin assignments, and package footprints differ, so they cannot be interchanged on the same PCB land pattern.
What logic families do the 74VHC244FT and 74VHCT74ATTR belong to?
The 74VHC244FT belongs to the VHC (Very High Speed CMOS) family, while the 74VHCT74ATTR belongs to the VHCT (Very High Speed CMOS with TTL-compatible inputs) family. VHCT devices feature input thresholds compatible with TTL logic levels, whereas VHC devices have CMOS-level input thresholds.
Can the 74VHC244FT and 74VHCT74ATTR operate from the same supply voltage?
Both devices are specified for a nominal supply voltage of 5 V, typically operating over a range of 4.5 V to 5.5 V. However, the VHCT74ATTR's TTL-compatible inputs allow it to interface with 5 V TTL logic directly, while the VHC244FT requires CMOS-level input swings for optimal performance.
What are the output drive capabilities of the 74VHC244FT compared to the 74VHCT74ATTR?
The 74VHC244FT is specified with a symmetric output drive of ±8 mA at 5 V, making it suitable for bus driving and line driving applications. The 74VHCT74ATTR provides a standard output drive of ±8 mA at 5 V as well, but its primary function is logic storage rather than bus driving.
Do both devices support 3-state outputs?
No. The 74VHC244FT features 3-state outputs controlled by two active-low output enable pins, allowing the outputs to be placed in a high-impedance state for bus sharing. The 74VHCT74ATTR has standard push-pull outputs and does not provide a high-impedance state.
What are the typical propagation delays for the 74VHC244FT and 74VHCT74ATTR?
At 5 V supply, the 74VHC244FT typically exhibits a propagation delay of approximately 3.8 ns. The 74VHCT74ATTR typically exhibits a propagation delay of approximately 5.0 ns from clock to output. These values are typical and subject to variation per manufacturer datasheet conditions.
Are the 74VHC244FT and 74VHCT74ATTR interchangeable in a design?
No. Because they perform different logic functions, have different pin counts, and belong to different logic families with different input threshold characteristics, they cannot be used as substitutes for one another without a complete redesign of the circuit and PCB layout.