Part A
74HC245D
Toshiba Semiconductor and Storage
- Lifecycle
- Active
- Stock
- 4218 PCS
- Package
- SOIC-14
- Series
- Logic - Buffers, Drivers, Receivers, Transceivers
Replacement verdict
Compatible functional replacement candidate
The 74HC244D and 74HC245D are both octal non-inverting buffers from the 74HC family, sharing identical supply voltage, logic levels, and package options. However, the 74HC244D provides unidirectional buffering with dual active-low output enables, while the 74HC245D is a bidirectional transceiver with direction control and a single active-low output enable. This fundamental difference in data flow architecture means the 74HC245D can serve as a functional substitute for the 74HC244D in unidirectional applications by fixing the direction pin, but the reverse substitution requires external logic to emulate bidirectional operation. Designers should verify direction control requirements and output enable polarity before committing to a drop-in replacement.
Logic Family
High match
Supply Voltage Range
High match
Output Enable Configuration
Validation required
Data Direction Architecture
Not compatible
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HC244D | 74HC245D | Why it matters |
|---|---|---|---|
| Logic Function | Octal buffer/line driver with 3-state outputs, non-inverting, dual enable (1OE, 2OE) | Octal bus transceiver with 3-state outputs, non-inverting, direction control (DIR) and output enable (OE) | Determines the core signal-flow behavior; the '244 is unidirectional with separate enables per nibble, while the '245 is bidirectional with a direction pin, so they are not functionally interchangeable in bus applications. |
| Directionality | Unidirectional (A to Y only) | Bidirectional (A to B or B to A selectable) | A bidirectional transceiver can replace a unidirectional buffer in many designs, but a unidirectional buffer cannot perform the reverse-direction data transfer required by a transceiver. |
| Control Pins | Two active-low output enables (1OE, 2OE) | One direction pin (DIR) and one active-low output enable (OE) | Pin function and control logic differ, so PCB routing and firmware/control signals must be redesigned when substituting one for the other. |
| Number of Channels | 8 | 8 | Matching channel count means both devices handle the same bus width, which is essential for drop-in bus buffering. |
| Output Type | 3-state (tri-state) | 3-state (tri-state) | Tri-state outputs allow the device to be disconnected from a shared bus, which is required for bus multiplexing and preventing contention. |
| Logic Family | HC (High-speed CMOS) | HC (High-speed CMOS) | Same logic family ensures compatible input thresholds, output drive, and speed characteristics, simplifying substitution. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | Identical operating voltage range means both parts work in the same 3.3 V or 5 V systems without level-shifting concerns. |
| Package | SO14 (SOIC-14) | SO20 (SOIC-20) | Different pin counts and package footprints mean the two devices are not pin-to-pin compatible and require different PCB land patterns. |
| Propagation Delay (typical) | ~11 ns at 4.5 V | ~11 ns at 4.5 V | Similar propagation delay ensures comparable timing performance in high-speed signal paths. |
| Output Drive Current | ±6 mA at 4.5 V | ±6 mA at 4.5 V | Matching drive current means both can drive similar loads, such as bus lines and moderate capacitive loads, without additional buffering. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC245D | 74HC244D |
|---|---|---|
| Series | 74HC | 74HC |
| Part Status | Active | Active |
| Logic Type | Transceiver, Non-Inverting | Buffer, Non-Inverting |
| Number of Elements | 1 | 2 |
| Number of Bits per Element | 8 | 4 |
| Output Type | 3-State | 3-State |
| Current - Output High Low | 7.8mA, 7.8mA | 7.8mA, 7.8mA |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Operating Temperature | -40°C ~ 125°C (TA) | -40°C ~ 85°C (TA) |
| Mounting Type | Surface Mount | Surface Mount |
Frequently asked questions
What is the main functional difference between the 74HC244D and the 74HC245D?
The 74HC244D is an octal non-inverting buffer/line driver with 3-state outputs that has a single active-low output enable (OE) pin controlling all eight channels. The 74HC245D is an octal bus transceiver with 3-state outputs that provides bidirectional data flow, using a direction control (DIR) pin and an active-low output enable (OE) pin to select transmit or receive mode.
Are the 74HC244D and 74HC245D pin-compatible in the SOIC-20 package?
No. Although both devices are offered in a 20-pin SOIC package, their pin functions differ. The 74HC244D uses pins for eight inputs, eight outputs, and one OE pin, while the 74HC245D uses pins for eight A-side I/Os, eight B-side I/Os, a DIR pin, and an OE pin. The pin assignments are not interchangeable, so the PCB layout must match the specific device.
Can the 74HC244D be used as a drop-in replacement for the 74HC245D?
No. The 74HC244D is unidirectional and cannot perform the bidirectional bus transfer function of the 74HC245D. Replacing a 74HC245D with a 74HC244D would require external wiring changes and would not provide the direction control needed for bidirectional bus operation.
What are the supply voltage and logic family specifications for both devices?
Both the 74HC244D and 74HC245D are members of the 74HC high-speed CMOS logic family. They typically operate over a supply voltage range of 2.0 V to 6.0 V, with characterized operation at 5 V. Inputs are CMOS-compatible, and outputs can drive standard CMOS and TTL-level loads within the specified fan-out limits.
How do the output drive capabilities of the 74HC244D and 74HC245D compare?
Both devices provide similar output drive strength as standard 74HC octal buffers/transceivers. At a 5 V supply, they typically source or sink several milliamps per output, sufficient for driving high-impedance CMOS inputs and moderate bus loads. For exact current ratings, consult the specific manufacturer datasheet, as values can vary slightly between vendors.
When should the 74HC245D be chosen over the 74HC244D?
The 74HC245D should be chosen when bidirectional data flow is required on a shared bus, such as between a microcontroller and a peripheral data bus. The 74HC244D is appropriate when only unidirectional buffering or line driving is needed, such as driving signals from one point to another without the need to reverse direction.
Do both devices feature 3-state outputs for bus isolation?
Yes. Both the 74HC244D and 74HC245D have 3-state outputs that can be placed in a high-impedance state via their respective output enable (OE) pins. This allows the outputs to be effectively disconnected from the bus, enabling multiple devices to share a common data line without contention.
Are the 74HC244D and 74HC245D available in identical package options?
Both devices are commonly available in a 20-pin SOIC package, designated with the "D" suffix in many manufacturer part numbers. However, other package options such as TSSOP, DIP, or QFN may also exist for each device. Always verify the specific package code and pinout from the manufacturer datasheet before designing or substituting.