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 74VHC238TTR are not functionally interchangeable. The 74VHC245FT is an octal bidirectional bus transceiver with three-state outputs, while the 74VHC238TTR is a 3-to-8 line decoder/demultiplexer. Their logic functions, pin configurations, and I/O structures are fundamentally different, making direct substitution impossible without redesigning the surrounding circuit.
Different logic function
Different pinout
Different I/O structure
Different package type
Parts at a glance
Part B
74VHC238TTR
意法半導體
- Lifecycle
- Active
- Stock
- 8997 件
- Package
- TSSOP-16
- Series
- 邏輯-訊號開關、多工器、解碼器
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 | 74VHC238TTR | Why it matters |
|---|---|---|---|
| Function | Octal Bus Transceiver, 3-state | 3-to-8 Line Decoder/Demultiplexer | These devices perform fundamentally different logic functions, so they are not functionally interchangeable in a circuit. |
| Logic Type | Bidirectional transceiver | Decoder/demultiplexer | The logic type determines the signal flow and control scheme, which must match the intended application. |
| Number of Channels / Outputs | 8 bidirectional channels | 8 outputs (from 3 inputs) | Channel count and output configuration affect how many signals can be routed or selected. |
| Output Type | 3-state | Active-low outputs | Output type determines whether outputs can be tri-stated for bus sharing or are always driven. |
| Control Inputs | Direction (DIR) and Output Enable (OE) | Three address inputs (A, B, C) and two enable inputs (G1, G2) | Control pin configuration dictates how the device is interfaced and controlled in a system. |
| Supply Voltage Range | 2.0 V to 5.5 V | 2.0 V to 5.5 V | Both devices operate over the same VHC supply range, allowing use in similar voltage environments. |
| Logic Family | VHC (Very High Speed CMOS) | VHC (Very High Speed CMOS) | Same logic family ensures compatible voltage thresholds and switching characteristics. |
| Propagation Delay (typical) | ~4.5 ns at 5 V | ~6.5 ns at 5 V | Propagation delay affects timing margins in high-speed digital systems. |
| Package | TSSOP-20 | TSSOP-16 | Different pin counts and package sizes affect PCB layout and footprint compatibility. |
| Pin Count | 20 | 16 | Pin count must match the PCB footprint; a mismatch prevents direct drop-in replacement. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74VHC245FT | 74VHC238TTR |
|---|---|---|
| Supplier | - | STMicroelectronics |
| Series | 74VHC | 74VHC |
| Part Status | Active | Obsolete |
| Type | - | Decoder/Demultiplexer |
| Circuit | - | 1 x 3:8 |
| Independent Circuits | - | 1 |
| Current - Output High Low | 8mA, 8mA | 8mA, 8mA |
| Voltage Supply Source | - | Single Supply |
| Voltage - Supply | 2V ~ 5.5V | 2V ~ 5.5V |
| Operating Temperature | -40°C ~ 125°C (TA) | -55°C ~ 125°C |
| Mounting Type | Surface Mount | Surface Mount |
| Logic Type | Transceiver, Non-Inverting | - |
| Number of Elements | 1 | - |
| Number of Bits per Element | 8 | - |
| Output Type | 3-State | - |
Frequently asked questions
What are the primary functions of the 74VHC245FT and 74VHC238TTR?
The 74VHC245FT is an octal bidirectional transceiver with 3-state outputs, designed for asynchronous two-way data transmission between buses. The 74VHC238TTR is a 3-to-8 line decoder/demultiplexer that accepts a 3-bit binary address and provides eight mutually exclusive active-LOW outputs.
Can the 74VHC245FT and 74VHC238TTR be used interchangeably in a design?
No. They perform fundamentally different logic functions. The 74VHC245FT is a bidirectional bus transceiver, while the 74VHC238TTR is a decoder/demultiplexer. They are not pin-compatible or functionally equivalent and cannot be substituted for one another.
What are the operating voltage ranges for these devices?
Both the 74VHC245FT and 74VHC238TTR operate over a supply voltage range of 2.0 V to 5.5 V, consistent with the VHC family specifications. This allows operation in 3.3 V and 5 V systems.
What package types are available for the 74VHC245FT and 74VHC238TTR?
The 74VHC245FT is offered in a TSSOP-20 package. The 74VHC238TTR is offered in a TSSOP-16 package. Package dimensions and pin counts differ, so PCB land patterns are not compatible between the two devices.
Do both devices have 3-state outputs?
No. The 74VHC245FT has 3-state outputs controlled by an output enable (OE) pin, allowing the outputs to be placed in a high-impedance state for bus sharing. The 74VHC238TTR has standard push-pull active-LOW outputs and does not provide a high-impedance state.
What is the difference in logic type between the 74VHC245FT and 74VHC238TTR?
The 74VHC245FT is a bidirectional transceiver with non-inverting outputs. The 74VHC238TTR is a decoder/demultiplexer with active-LOW outputs, where only one of eight outputs is asserted based on the 3-bit address input.
Are these devices compatible with standard CMOS logic levels?
Yes. Both the 74VHC245FT and 74VHC238TTR are VHC-family CMOS devices with standard CMOS input thresholds and are compatible with other 5 V and 3.3 V CMOS logic families when operated at the appropriate supply voltage.
What are typical applications for each device?
The 74VHC245FT is typically used for bus interfacing, data transmission between bidirectional buses, and signal buffering in microprocessor or memory systems. The 74VHC238TTR is typically used for address decoding, memory chip selection, and demultiplexing in digital systems.