Part A
74VHC245FT
東芝電晶體與存儲
- Lifecycle
- Active
- Stock
- 4188 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 74VHC245FT and 74VHCT74ATTR are functionally unrelated devices and cannot serve as substitutes for one another. The 74VHC245FT is an octal bidirectional bus transceiver with three-state outputs, while the 74VHCT74ATTR is a dual D-type flip-flop with complementary outputs. They differ in logic function, channel count, pin configuration, and package type, making direct replacement impossible without complete circuit redesign.
Different logic function
Different channel count
Different pin configuration
Different package type
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 | 74VHC245FT | 74VHCT74ATTR | Why it matters |
|---|---|---|---|
| Logic Function | Octal Bus Transceiver, 3-state | Dual D-Type Flip-Flop with Preset and Clear | These are fundamentally different logic functions, so they are not functionally substitutable in a circuit. |
| Logic Family | VHC (Very High Speed CMOS) | VHCT (VHC with TTL-compatible inputs) | VHCT inputs are TTL-voltage compatible, while VHC inputs are CMOS-level; this affects interfacing with other logic levels. |
| 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 operation to 5 V systems, while the VHC device supports lower-voltage operation. |
| Number of Channels / Bits | 8 (octal) | 2 (dual flip-flop) | Channel count determines how many signals can be handled, directly affecting circuit capacity and board layout. |
| Output Type | 3-state (tri-state) outputs | Standard push-pull outputs | Tri-state outputs allow bus sharing and high-impedance isolation, which the flip-flop outputs do not provide. |
| Direction Control | Direction pin (A-to-B or B-to-A) | Not applicable (no direction control) | Bidirectional data flow is a key feature of the transceiver and is absent in the flip-flop. |
| Clock Input | None | Yes (edge-triggered) | The flip-flop requires a clock for state changes, while the transceiver is purely combinational. |
| Propagation Delay (typical) | ~4.5 ns at 5 V | ~6.5 ns at 5 V | Different delays affect timing margins and maximum operating frequency in synchronous designs. |
| 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, so thermal suitability is equivalent. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74VHC245FT | 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 | 1 | 2 |
| Number of Bits per Element | 8 | 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 | Transceiver, Non-Inverting | - |
Frequently asked questions
What are the primary functional differences between the 74VHC245FT and the 74VHCT74ATTR?
The 74VHC245FT is an octal bidirectional transceiver with 3-state outputs, designed for bus-oriented applications. 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.
Do the 74VHC245FT and 74VHCT74ATTR use the same logic family technology?
Both devices belong to the VHC/VHCT CMOS logic families. The 74VHC245FT is VHC (advanced high-speed CMOS), while the 74VHCT74ATTR is VHCT (advanced high-speed CMOS with TTL-compatible inputs). The VHCT variant is specifically designed for interfacing with TTL logic levels.
Are the input voltage thresholds different between the 74VHC245FT and 74VHCT74ATTR?
Yes. The 74VHC245FT (VHC family) has CMOS-level inputs typically referenced to VCC, while the 74VHCT74ATTR (VHCT family) has TTL-compatible input thresholds, allowing direct interface with 5 V TTL logic when operated at 5 V VCC. Exact threshold values should be verified from the respective manufacturer datasheets.
Can the 74VHC245FT and 74VHCT74ATTR operate from the same supply voltage range?
Both devices are typically specified for a 2.0 V to 5.5 V VCC operating range, with the VHCT device optimized for 5 V TTL-compatible operation. Actual guaranteed operating ranges and electrical characteristics must be confirmed from the official manufacturer datasheets for each part.
Are the 74VHC245FT and 74VHCT74ATTR available in the same package type?
No. The 74VHC245FT is typically offered in a TSSOP-20 package, while the 74VHCT74ATTR is typically offered in a TSSOP-14 package. Package differences reflect their different pin counts and functions, and they are not pin-to-pin compatible.
Can the 74VHC245FT be used to replace the 74VHCT74ATTR in an existing design?
No. The two devices have different logic functions, pin counts, and package types. The 74VHC245FT is an octal transceiver, while the 74VHCT74ATTR is a dual flip-flop. Direct substitution is not possible without redesigning the circuit.
What are the typical applications for each device?
The 74VHC245FT is commonly used for bidirectional bus buffering, signal isolation, and data transmission between buses. The 74VHCT74ATTR is used for data storage, edge-triggered latching, and synchronization functions in digital systems. Application suitability depends on the specific design requirements.
Do both devices support 3-state outputs?
The 74VHC245FT features 3-state outputs for bus connection and disconnection. The 74VHCT74ATTR has standard push-pull outputs and does not provide a 3-state (high-impedance) output mode. This is a critical difference for bus-oriented designs.