Part A
74HC245D
Компания Toshiba Semiconductor и Storage
- Lifecycle
- Active
- Stock
- 4218 ПКС
- Package
- SOIC-14
- Series
- Логика - буферы, драйверы, приемники, передатчики
Replacement verdict
Not a drop-in replacement
The 74HC245D and 74HC21D,653 are functionally unrelated logic ICs and cannot serve as substitutes for one another. The 74HC245D is an octal bidirectional bus transceiver with 3-state outputs, while the 74HC21D,653 is a dual 4-input AND gate. Their logic functions, pin configurations, and I/O characteristics are fundamentally different, making direct replacement impossible without complete circuit redesign.
Different logic function
Different pin configuration
Different I/O structure
Different output type
Parts at a glance
Part B
74HC21D,653
Компания NXP Semiconductors
- Lifecycle
- Active
- Stock
- 8890 ПКС
- Series
- Логика - Ворота и инверторы
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HC245D | 74HC21D,653 | Why it matters |
|---|---|---|---|
| Logic Function | Octal bus transceiver with 3-state outputs | Dual 4-input AND gate | These devices perform fundamentally different logic functions, so they are not functionally interchangeable in a circuit. |
| Number of Channels / Gates | 8 bidirectional channels | 2 gates (4-input each) | Channel count determines how many signal lines the device can handle simultaneously. |
| Direction Control | Direction pin (DIR) and output enable (OE) | None (unidirectional logic gate) | Bidirectional control allows data flow in either direction, which a fixed AND gate cannot provide. |
| Output Type | 3-state (tri-state) outputs | Standard push-pull CMOS output | Tri-state outputs allow bus sharing by disconnecting the output, while push-pull outputs are always driven. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | Both parts operate over the same HC-family supply range, so voltage compatibility is equivalent. |
| Logic Family | 74HC (High-speed CMOS) | 74HC (High-speed CMOS) | Same logic family means comparable input thresholds, noise margins, and drive characteristics. |
| Propagation Delay (typical) | ~8 ns at 4.5 V | ~11 ns at 4.5 V | Propagation delay affects maximum operating speed and timing margins in the target design. |
| Output Drive Current | ±6 mA at 4.5 V | ±4 mA at 4.5 V | Drive current determines the load the output can reliably sink or source. |
| Package | SO16 (SOIC-16) | SO14 (SOIC-14) | Different pin counts and package sizes affect PCB footprint and layout compatibility. |
| Pin Count | 16 pins | 14 pins | Pin count must match the board footprint; a mismatch prevents direct drop-in replacement. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC245D | 74HC21D,653 |
|---|---|---|
| Supplier | - | Rochester Electronics, LLC |
| Part Status | Active | Active |
| Series | 74HC | - |
| Logic Type | Transceiver, Non-Inverting | - |
| Number of Elements | 1 | - |
| Number of Bits per Element | 8 | - |
| Output Type | 3-State | - |
| Current - Output High Low | 7.8mA, 7.8mA | - |
| Voltage - Supply | 2V ~ 6V | - |
| Operating Temperature | -40°C ~ 125°C (TA) | - |
| Mounting Type | Surface Mount | - |
Frequently asked questions
What are the primary functions of the 74HC245D and the 74HC21D,653?
The 74HC245D is an octal bus transceiver with 3-state outputs, designed for bidirectional asynchronous communication between data buses. The 74HC21D,653 is a dual 4-input AND gate that provides a logic high output only when all four inputs of a gate are high.
Can the 74HC245D and 74HC21D,653 be used interchangeably in a circuit design?
No. They perform fundamentally different logic functions. The 74HC245D is a bus transceiver for data routing, while the 74HC21D,653 is a logic gate for Boolean AND operations. They are not pin-compatible or functionally equivalent.
What are the operating voltage ranges for the 74HC245D and 74HC21D,653?
Both devices are members of the 74HC logic family and typically operate over a supply voltage range of 2.0 V to 6.0 V. Specific limits should be confirmed from the respective manufacturer datasheets.
What package types are available for the 74HC245D and 74HC21D,653?
The 74HC245D is commonly offered in a 20-pin SOIC package. The 74HC21D,653 is typically supplied in a 14-pin SOIC package. Package designations may vary by manufacturer; always verify the exact orderable part number.
How do the output drive capabilities of the 74HC245D and 74HC21D,653 compare?
Both devices are standard 74HC CMOS logic parts. Their output drive currents are typically specified in the datasheet, with symmetric source and sink currents. The 74HC245D includes 3-state outputs, while the 74HC21D,653 provides standard push-pull outputs.
Are the 74HC245D and 74HC21D,653 compatible with 5 V TTL logic levels?
Yes, when operated at a 5 V supply, both 74HC devices are generally compatible with TTL input voltage thresholds. However, input and output voltage ratings must be checked against the specific datasheet to ensure proper interfacing.
What are the typical propagation delays for the 74HC245D and 74HC21D,653?
Propagation delay depends on supply voltage, load capacitance, and temperature. For both devices, typical values at 5 V are in the low nanosecond range. Consult the manufacturer datasheet for guaranteed maximum limits.
Do the 74HC245D and 74HC21D,653 have any special input or output protection features?
Both devices include standard ESD protection and input clamping diodes as part of the 74HC family. They do not include additional fault-tolerant or overvoltage-tolerant features unless explicitly stated in the datasheet.