Part A
74VHC245FT
Toshiba Semiconductor et stockage
- Lifecycle
- Active
- Stock
- 4188 PCS
- Package
- TSSOP-20
- Series
- Logique - Buffers, lecteurs, récepteurs, émetteurs - récepteurs
Replacement verdict
Not a drop-in replacement
The 74VHC245FT and 74VHC20TTR are not functionally interchangeable. The 74VHC245FT is an octal bus transceiver with 3-state outputs and direction control, while the 74VHC20TTR is a dual 4-input NAND gate. They differ in logic function, channel configuration, pinout, and control interface, so substitution requires a complete circuit redesign rather than a direct swap.
Different logic function
Different channel count
Different pinout
Different control interface
Parts at a glance
Part B
74VHC20TTR
Semi - conducteurs optiques
- Lifecycle
- Active
- Stock
- 2895 PCS
- Series
- Logique - portes et Onduleurs
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 | 74VHC20TTR | Why it matters |
|---|---|---|---|
| Logic Function | Octal Bus Transceiver, 3-State | Dual 4-Input NAND Gate | These devices perform completely different logic functions, so they are not functionally interchangeable in a circuit. |
| Number of Channels / Gates | 8 channels (bidirectional) | 2 gates (4-input each) | Channel/gate count determines how many signals can be processed, directly affecting circuit architecture. |
| Output Type | 3-State | Push-Pull | 3-state outputs allow bus sharing, while push-pull outputs cannot be tied together without contention. |
| Direction Control | Direction pin (A-to-B or B-to-A) | None (unidirectional logic) | Bidirectional control is essential for bus transceiver applications but absent in fixed logic gates. |
| Propagation Delay (typ.) | ~4.5 ns at 5 V | ~5.5 ns at 5 V | Propagation delay affects maximum operating frequency and timing margins in synchronous designs. |
| Supply Voltage Range | 2.0 V to 5.5 V | 2.0 V to 5.5 V | Both support the same VHC voltage range, allowing use in 3.3 V and 5 V mixed systems. |
| Logic Family | VHC (Very High-Speed CMOS) | VHC (Very High-Speed CMOS) | Same logic family ensures compatible input/output thresholds and noise margins. |
| Package | TSSOP-20 | TSSOP-14 | Different pin counts and footprints prevent direct PCB drop-in replacement. |
| Operating Temperature Range | -40 °C to +85 °C | -55 °C to +125 °C | Wider temperature range in the 74VHC20TTR suits harsher environments and automotive/industrial use. |
| Pin Count | 20 | 14 | Pin count determines board layout compatibility and available I/O for the application. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74VHC245FT | 74VHC20TTR |
|---|---|---|
| Supplier | - | STMicroelectronics |
| Series | 74VHC | 74VHC |
| Part Status | Active | Obsolete |
| Logic Type | Transceiver, Non-Inverting | NAND Gate |
| Number of Circuits | - | 2 |
| Number of Inputs | - | 4 |
| Voltage - Supply | 2V ~ 5.5V | 2V ~ 5.5V |
| Current - Quiescent (Max) | - | 2 µA |
| Current - Output High Low | 8mA, 8mA | 8mA, 8mA |
| Logic Level - Low | - | 0.5V |
| Logic Level - High | - | 1.5V |
| Max Propagation Delay @ V Max CL | - | 7ns @ 5V, 50pF |
| Operating Temperature | -40°C ~ 125°C (TA) | -55°C ~ 125°C |
| Mounting Type | Surface Mount | Surface Mount |
| Number of Elements | 1 | - |
| Number of Bits per Element | 8 | - |
| Output Type | 3-State | - |
Frequently asked questions
What are the primary functional differences between the 74VHC245FT and the 74VHC20TTR?
The 74VHC245FT is an octal bus transceiver with 3-state outputs, designed for bidirectional data transfer between two buses. The 74VHC20TTR is a dual 4-input NAND gate, providing a logic function rather than bus interfacing. They serve fundamentally different roles in digital circuits.
Are the 74VHC245FT and 74VHC20TTR pin-compatible?
No. The 74VHC245FT typically uses a 20-pin package (e.g., TSSOP20), while the 74VHC20TTR uses a 14-pin package (e.g., TSSOP14). Pin counts, pin functions, and PCB land patterns differ, so they are not drop-in replacements.
Can the 74VHC245FT and 74VHC20TTR operate from the same supply voltage range?
Yes. Both are 74VHC-series CMOS devices 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 V. Always verify the exact limits in the respective manufacturer datasheets.
What are the typical propagation delays for the 74VHC245FT and 74VHC20TTR?
At 5 V supply, the 74VHC245FT typically exhibits a propagation delay of about 3.5 ns to 5 ns depending on direction and load. The 74VHC20TTR typically shows a propagation delay of about 4 ns to 6 ns. These values are load-dependent and should be confirmed from the latest datasheets.
Do both devices have 3-state outputs?
No. The 74VHC245FT has 3-state outputs controlled by direction and output-enable pins, allowing bus isolation. The 74VHC20TTR has standard push-pull outputs and does not provide a high-impedance state.
Which device is suitable for bus-oriented applications?
The 74VHC245FT is intended for bus-oriented applications because it can drive bidirectional buses and enter a high-impedance state. The 74VHC20TTR is a general-purpose logic gate and is not designed for bus interfacing.
Are the 74VHC245FT and 74VHC20TTR available in similar package types?
Both are offered in surface-mount packages such as TSSOP, but with different pin counts: 20 pins for the 74VHC245FT and 14 pins for the 74VHC20TTR. Package outlines and thermal characteristics also differ; consult the specific manufacturer datasheet for exact dimensions.