Part A
74HCT245D
Toshiba Semiconductor và lưu trữ
- Lifecycle
- Active
- Stock
- 6073 PCS
- Package
- SOIC-14
- Series
- Logic - Buffers, Drivers, Receivers, Transceivers
Replacement verdict
Not a drop-in replacement
The 74HCT245D and 74HCT7403D,518 are not functionally interchangeable. The 74HCT245D is an octal bus transceiver with 3-state outputs, while the 74HCT7403D,518 is a quad 2-input NAND buffer with open-drain outputs. They differ in logic function, channel count, output type, and pinout, so direct substitution is not possible without circuit redesign.
Different logic function
Different channel count
Different output type
Different pinout
Parts at a glance
Part B
74HCT7403D,518
NXP Hoa Kỳ Inc.
- Lifecycle
- Active
- Stock
- 3207 PCS
- Package
- SOIC-16
- Series
- Logic - FIFOs Memory
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HCT245D | 74HCT7403D,518 | Why it matters |
|---|---|---|---|
| Logic Function | Octal Bus Transceiver, 3-State | Quad 2-Input NAND Gate, Open-Collector | The core logic function determines whether the parts are functionally interchangeable; a transceiver and a NAND gate perform entirely different operations. |
| Number of Channels | 8 | 4 | Channel count defines how many independent signal paths the device can handle, directly affecting circuit capacity and board layout. |
| Output Type | 3-State | Open-Collector | Output configuration affects bus sharing, drive capability, and whether external pull-up resistors are required. |
| Direction Control | Bidirectional (DIR pin) | Unidirectional | Bidirectional capability allows data flow in both directions, which is essential for bus interfacing but not provided by fixed-direction logic gates. |
| Propagation Delay (tpd) | ~14 ns (typ, 5 V) | ~20 ns (typ, 5 V) | Propagation delay influences maximum operating frequency and timing margins in synchronous systems. |
| Output Drive Current (IOH/IOL) | ±6 mA | -0.1 mA / 8 mA (open-collector sink) | Drive current determines the ability to drive loads and interface with other logic families or LEDs. |
| Supply Voltage Range | 4.5 V to 5.5 V | 4.5 V to 5.5 V | Matching supply voltage ranges ensures both devices can operate in the same power environment without level shifting. |
| Logic Family | HCT (TTL-compatible CMOS) | HCT (TTL-compatible CMOS) | Same logic family ensures compatible input thresholds and output levels for direct interfacing. |
| Package Type | SOIC-20 (D suffix) | SOIC-14 (D suffix) | Package footprint and pin count must match the PCB layout for physical compatibility. |
| Operating Temperature Range | -40 °C to +125 °C | -40 °C to +85 °C | Temperature range affects reliability and suitability for industrial or automotive environments. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HCT245D | 74HCT7403D,518 |
|---|---|---|
| Supplier | - | NXP USA Inc. |
| Series | 74HCT | 74HCT |
| Part Status | Active | Obsolete |
| Memory Size | - | 256 (64 x 4) |
| Function | - | Asynchronous, Synchronous |
| Data Rate | - | 30MHz |
| Access Time | - | 61ns |
| Voltage - Supply | 4.5V ~ 5.5V | 4.5 V ~ 5.5 V |
| Current - Supply (Max) | - | 1mA |
| Bus Directional | - | Uni-Directional |
| Expansion Type | - | Depth, Width |
| Programmable Flags Support | - | No |
| Retransmit Capability | - | No |
| FWFT Support | - | No |
| Operating Temperature | -40°C ~ 125°C (TA) | -40°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 | - |
| Current - Output High Low | 6mA, 6mA | - |
Frequently asked questions
What are the primary functional differences between the 74HCT245D and the 74HCT7403D,518?
The 74HCT245D is an octal bus transceiver with 3-state outputs, designed for bidirectional asynchronous communication between data buses. The 74HCT7403D,518 is a quad 2-input NAND buffer with open-drain outputs, intended for logic gating and wired-OR applications. They serve fundamentally different logic functions and are not pin-to-pin or function-to-function equivalents.
Are the 74HCT245D and 74HCT7403D,518 pin-compatible?
No. The 74HCT245D is typically supplied in a 20-pin SOIC package, while the 74HCT7403D,518 is supplied in a 14-pin SOIC package. Pin counts, pin assignments, and package dimensions differ, so they cannot be interchanged on the same PCB footprint without redesign.
Can the 74HCT245D and 74HCT7403D,518 operate from the same supply voltage?
Yes. Both devices are members of the 74HCT logic family and are specified for a nominal supply voltage of 5 V, with a typical operating range of 4.5 V to 5.5 V. This allows them to be used in the same 5 V logic system, provided the functional and pinout differences are respected.
What is the difference in output drive capability between the 74HCT245D and the 74HCT7403D,518?
The 74HCT245D provides standard 3-state push-pull outputs with symmetrical source and sink current capability, typically ±6 mA per output. The 74HCT7403D,518 has open-drain outputs, which can sink current but cannot source current, and typically sink 4 mA. The open-drain configuration requires external pull-up resistors for logic-high output levels.
Which device is suitable for bidirectional bus interfacing?
The 74HCT245D is the correct choice for bidirectional bus interfacing. It features an octal transceiver with direction control and output enable inputs, allowing data to flow in either direction between two buses. The 74HCT7403D,518 is a unidirectional logic gate and cannot perform bus transceiver functions.
Do both devices support 3-state output operation?
No. The 74HCT245D supports 3-state outputs, enabling high-impedance isolation from the bus when disabled. The 74HCT7403D,518 has open-drain outputs, which are not 3-state; when the output transistor is off, the output is pulled high by an external resistor rather than entering a high-impedance state.
What are the typical propagation delay characteristics of these two devices?
For the 74HCT245D, the typical propagation delay from A to B or B to A is approximately 12 ns at 5 V. For the 74HCT7403D,518, the typical propagation delay from input to output is approximately 15 ns at 5 V. Exact values depend on load conditions and should be verified from the respective manufacturer datasheets.
Can the 74HCT7403D,518 be used to replace the 74HCT245D in an existing design?
No. The two devices differ in logic function, pin count, package, output type, and control signals. The 74HCT7403D,518 cannot perform bidirectional bus transceiver operations, lacks 3-state outputs, and has a different pinout. Direct replacement is not possible without significant circuit redesign.