NXP N74F373D Octal D-Type Transparent Latch with 3-State Outputs: Datasheet Overview and Application Notes
The NXP N74F373D is a high-performance, octal D-type transparent latch designed with 3-state outputs, making it a fundamental component in modern digital systems for temporary data storage and bus interfacing. Fabricated using advanced bipolar technology, this IC is part of the N74F high-speed logic family, offering a compelling blend of speed, drive capability, and functional density.
A primary feature of the N74F373D is its eight latches with a common output enable (OE) and latch enable (LE) input. When the LE input is held high, the Q outputs follow the data (D) inputs transparently. A high-to-low transition on the LE signal latches the data at the D inputs at that moment, storing it until LE is taken high again. The 3-state outputs are controlled by the OE pin; a low level on OE activates the outputs, while a high level places them in a high-impedance (Hi-Z) state. This is critical for connecting multiple devices to a shared data bus without causing contention, as only one device can drive the bus at any given time.
Key electrical characteristics from the datasheet highlight its robust performance. The device operates with a standard 5V power supply and features TTL-compatible inputs and outputs. It boasts a typical propagation delay (tPLH/tPHL) of just 5.5 ns, enabling its use in high-speed applications. Furthermore, the outputs can sink up to 12 mA and source 3 mA, providing sufficient current to drive multiple inputs or indicators directly.
Application Notes and Circuit Design Considerations
The N74F373D is ubiquitously employed as an I/O port latch in microprocessorbased systems. It acts as a buffer between the microprocessor's data bus and external peripherals, temporarily holding output data or input status. For example, in an 8-bit system, a single N74F373D can latch the lower address byte from a multiplexed address/data bus during a bus cycle.
When designing with this IC, several factors are crucial:
1. Bus Contention Prevention: The system controller must ensure the OE signal is deactivated (high) before another device is allowed to drive the shared bus, preventing damaging short-circuit currents.
2. Power Supply Decoupling: A 0.1 μF ceramic decoupling capacitor should be placed as close as possible to the VCC and GND pins to suppress high-frequency noise generated by fast switching transitions.
3. Unused Input Handling: To ensure predictable operation and minimize power consumption, unused inputs must never be left floating. They should be tied to VCC or GND through a resistor, typically 1 kΩ to 10 kΩ.
4. Thermal Management: While the device can drive significant current, the total power dissipation (calculated as PD = VCC ICC + (VOL IOL) for each output) should be monitored to ensure the junction temperature remains within safe limits, especially in high-temperature environments.
The NXP N74F373D remains a highly reliable and efficient solution for data latching and bus driving tasks. Its high-speed operation, significant output drive capability, and 3-state output control make it an indispensable building block for system designers working on data acquisition, port expansion, and any architecture employing a shared bus. For modern designs, it offers a proven, robust interface between processors and the outside world.
Keywords:
Octal D-Type Latch
3-State Outputs
Bus Interface
Data Storage
N74F Logic Family
