Part A
74VHC244FT
Toshiba Semiconductor et stockage
- Lifecycle
- Active
- Stock
- 2156 PCS
- Package
- TSSOP-20
- Series
- Logique - Buffers, lecteurs, récepteurs, émetteurs - récepteurs
Replacement verdict
Not a drop-in replacement
The 74VHC244FT and 74VHC238TTR are not functionally interchangeable. The 74VHC244FT is a quad non-inverting buffer/line driver with 3-state outputs, while the 74VHC238TTR is a 3-to-8 line decoder/demultiplexer. Their logic functions, pin configurations, and output characteristics are fundamentally different, making direct substitution impossible without circuit redesign.
Different logic function
Different output type
Different pinout
Different channel count
Parts at a glance
Part B
74VHC238TTR
Semi - conducteurs optiques
- Lifecycle
- Active
- Stock
- 8997 PCS
- Package
- TSSOP-16
- Series
- Logique - commutateurs de signaux, multiplexeurs, décodeurs
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 | 74VHC238TTR | Why it matters |
|---|---|---|---|
| Logic Function | Octal Buffer/Line Driver with 3-State Outputs | 3-to-8 Line Decoder/Demultiplexer | The core logic function determines whether the devices are functionally interchangeable; these two parts perform entirely different operations. |
| Number of Outputs | 8 | 8 | Both provide eight outputs, but the output behavior differs (buffered data vs. decoded one-of-eight selection). |
| Output Type | 3-State | Active-Low (non-3-state) | 3-state outputs allow bus sharing and high-impedance isolation, which the decoder does not provide. |
| Number of Inputs | 8 (data inputs) plus 2 output-enable inputs | 3 (address/select inputs) plus 3 enable inputs | Input count and configuration dictate how the device interfaces with surrounding logic. |
| Supply Voltage Range | 2.0 V to 5.5 V | 2.0 V to 5.5 V | Both operate over the same VHC supply range, so power-supply compatibility is not a differentiator. |
| Propagation Delay (typical) | ~3.8 ns at 5 V | ~5.0 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 footprint and layout compatibility. |
| Pin Count | 20 | 16 | Pin count must match the board footprint for a drop-in replacement. |
| Operating Temperature Range | -40 °C to +85 °C | -40 °C to +85 °C | Both support the same industrial temperature range, so environmental compatibility is equivalent. |
| Logic Family | VHC (Very High-Speed CMOS) | VHC (Very High-Speed CMOS) | Same logic family ensures comparable input/output thresholds and noise immunity. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74VHC244FT | 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 | Buffer, Non-Inverting | - |
| Number of Elements | 2 | - |
| Number of Bits per Element | 4 | - |
| Output Type | 3-State | - |
Frequently asked questions
What are the primary functions of the 74VHC244FT and 74VHC238TTR?
The 74VHC244FT is an octal non-inverting buffer/line driver with 3-state outputs, designed to drive high-capacitance loads or bus lines. The 74VHC238TTR is a 3-to-8 line decoder/demultiplexer that accepts a 3-bit binary address and activates one of eight mutually exclusive outputs.
Can the 74VHC244FT and 74VHC238TTR be used interchangeably in a design?
No. They perform fundamentally different logic functions. The 74VHC244FT provides buffering and 3-state bus driving, while the 74VHC238TTR performs address decoding and demultiplexing. Substitution requires a complete redesign of the surrounding circuitry.
What are the package and pin count differences between the 74VHC244FT and 74VHC238TTR?
The 74VHC244FT is typically offered in a 20-pin TSSOP package (e.g., TSSOP-20B). The 74VHC238TTR is typically offered in a 16-pin TSSOP package (e.g., TSSOP-16). Pin counts and pinouts are not compatible.
Do both devices operate from the same supply voltage range?
Yes. Both the 74VHC244FT and 74VHC238TTR are members of the VHC logic family and operate from a supply voltage range of 2.0 V to 5.5 V, with typical operation at 3.3 V or 5.0 V.
What are the output drive characteristics of the 74VHC244FT compared to the 74VHC238TTR?
The 74VHC244FT provides 3-state outputs with a specified output drive of ±8 mA at 5.0 V, suitable for bus driving. The 74VHC238TTR provides standard CMOS outputs with a specified output drive of ±8 mA at 5.0 V, but its outputs are not 3-state; they are either active low or high depending on the enable inputs.
How do the control inputs differ between the 74VHC244FT and 74VHC238TTR?
The 74VHC244FT has two active-low output enable inputs (1OE and 2OE) that control the 3-state condition of the outputs. The 74VHC238TTR has three enable inputs (two active-low and one active-high) that must be set appropriately to enable the decoder outputs.
Are the 74VHC244FT and 74VHC238TTR available in the same temperature grade?
Both devices are typically specified for the industrial temperature range of -40 °C to +85 °C, as indicated in their respective manufacturer datasheets.
What is the propagation delay difference between the 74VHC244FT and 74VHC238TTR?
At 5.0 V supply, the 74VHC244FT typically has a propagation delay of approximately 3.8 ns to 5.5 ns. The 74VHC238TTR typically has a propagation delay of approximately 5.0 ns to 7.5 ns. Exact values depend on load conditions and are specified in the respective datasheets.