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 74VHC126TTR are not functionally interchangeable. The 74VHC245FT is an octal bus transceiver with dual enable control and bidirectional data flow, while the 74VHC126TTR is a quad bus buffer with 3-state outputs and unidirectional signal paths. Their differences in logic function, channel count, control architecture, and pinout prevent direct substitution without circuit redesign.
Different logic function
Different channel count
Different control architecture
Different pinout
Parts at a glance
Part B
74VHC126TTR
意法半導體
- Lifecycle
- Active
- Stock
- 4191 件
- Package
- TSSOP-14
- Series
- 邏輯-緩衝器、驅動器、接收器、收發器
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 | 74VHC126TTR | Why it matters |
|---|---|---|---|
| Logic Function | Octal Bus Transceiver, 3-state | Quad Bus Buffer, 3-state | Defines the core function; a transceiver supports bidirectional data flow while a buffer is unidirectional, so they are not directly substitutable. |
| Number of Channels | 8 | 4 | Channel count determines how many signal lines can be handled; fewer channels may require additional components. |
| Direction Control | Direction pin (A-to-B or B-to-A) | Fixed (A-to-Y only) | Bidirectional capability is essential for bus applications; a fixed-direction buffer cannot replace a transceiver in bidirectional designs. |
| Output Enable | Common OE (active low) | Individual OE per channel (active low) | Independent enables allow selective channel control, while a common enable controls all channels together, affecting system flexibility. |
| Supply Voltage Range | 2.0 V to 5.5 V | 2.0 V to 5.5 V | Compatible supply range ensures both parts can operate in the same logic-level environment. |
| Output Type | 3-state | 3-state | 3-state outputs allow high-impedance isolation, which is critical for shared bus architectures. |
| Logic Family | VHC (Very High Speed CMOS) | VHC (Very High Speed CMOS) | Same logic family ensures compatible switching thresholds, speed, and noise margins. |
| Package | TSSOP-20 | TSSOP-14 | Different pin counts and footprints prevent direct PCB drop-in replacement without layout changes. |
| Propagation Delay (typ) | ~4.5 ns at 5 V | ~4.5 ns at 5 V | Similar delay supports comparable timing performance, but must be verified against exact datasheet conditions. |
| Pin Count | 20 | 14 | Pin count affects board layout and available I/O; mismatched pin counts mean the parts are not pin-compatible. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74VHC245FT | 74VHC126TTR |
|---|---|---|
| Supplier | - | STMicroelectronics |
| Series | 74VHC | 74VHC |
| Part Status | Active | Obsolete |
| Logic Type | Transceiver, Non-Inverting | Buffer, Non-Inverting |
| Number of Elements | 1 | 4 |
| Number of Bits per Element | 8 | 1 |
| Output Type | 3-State | 3-State |
| Current - Output High Low | 8mA, 8mA | 8mA, 8mA |
| Voltage - Supply | 2V ~ 5.5V | 2V ~ 5.5V |
| Operating Temperature | -40°C ~ 125°C (TA) | -55°C ~ 125°C (TA) |
| Mounting Type | Surface Mount | Surface Mount |
Frequently asked questions
What are the primary functional differences between the 74VHC245FT and the 74VHC126TTR?
The 74VHC245FT is an octal bus transceiver with 3-state outputs, designed for bidirectional asynchronous communication between data buses. The 74VHC126TTR is a quad bus buffer with 3-state outputs, featuring four independent non-inverting buffers with active-high enable inputs. The 74VHC245FT provides eight transceiver channels with direction control, while the 74VHC126TTR provides four unidirectional buffer channels.
Are the 74VHC245FT and 74VHC126TTR pin-to-pin compatible?
No. The 74VHC245FT is typically supplied in a 20-pin package (such as TSSOP-20), while the 74VHC126TTR is supplied in a 14-pin package (such as TSSOP-14). The pin counts, pin functions, and PCB land patterns differ, so they are not drop-in replacements for each other.
Can the 74VHC245FT and 74VHC126TTR operate from the same supply voltage range?
Yes. Both devices are members of the VHC logic family and are specified for a supply voltage range of 2.0 V to 5.5 V, with typical operation at 3.3 V or 5.0 V. This allows both to be used in mixed-voltage systems within that range.
What is the difference in channel count and data flow direction between these two devices?
The 74VHC245FT has eight channels that can be configured for either A-to-B or B-to-A data flow via a direction control pin, making it suitable for bidirectional bus interfacing. The 74VHC126TTR has four channels that are strictly unidirectional (input to output), with each channel independently controlled by its own active-high output enable pin.
Do both the 74VHC245FT and 74VHC126TTR have 3-state outputs?
Yes. Both devices feature 3-state outputs that can be placed in a high-impedance state. On the 74VHC245FT, the outputs are disabled via the output enable pin. On the 74VHC126TTR, each of the four buffers has its own output enable pin, allowing independent high-impedance control per channel.
Which device is more suitable for driving a shared bidirectional data bus?
The 74VHC245FT is more suitable for shared bidirectional data bus applications because it integrates eight transceiver channels with a direction control pin, allowing a single device to manage both transmit and receive paths. The 74VHC126TTR is intended for unidirectional buffering and would require external routing or additional devices to implement bidirectional bus control.
Are the 74VHC245FT and 74VHC126TTR interchangeable in existing designs?
No. Due to differences in package pin count, channel count, direction control, and enable logic, the two devices are not interchangeable without redesigning the PCB layout and verifying signal integrity, timing, and control logic against the manufacturer datasheets.