74AC646SC

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The 74AC646SC is a high-performance, logic buffer device with bus-hold data inputs that feature reduced threshold levels for increased noise margin and improved AC performance. It is designed for applications such as system logic and data distribution, address and data latching, and redrive of AC signals from sources such as a microprocessor. The device performs efficient buffering and translation of control signals in multiplexing and bus management systems, system data rescaling, as well as logic bus-expansion and bus-termination applications.

Application Field

The 74AC646SC is a bidirectional hex buffer. It can be used in multiple types of applications such as peripheral devices, microprocessor-based systems, memory buffering, FIFO control in communication systems, and control or clock signals in others. The 74AC646SC could also be used as a line receiver in logic systems. Furthermore, the device is typically used as an interface between one bus to another.

Working Principle

The 74AC646SC is a bus transceiver device which contains six independent buffers. Each of the buffers includes three-state outputs, active low output-enable (OE) inputs, and active-low input-enable (IE) inputs. When the output-enable (OE) inputs are high, the outputs are in the high-impedance state and do not drive the bus line. When the IE inputs are low, the input data is held by the bus-hold feature and does not affect the logic levels at the outputs. When both the OE and IE inputs are low, the data at the inputs will appear at the outputs.

The logic levels of both the input and output can be configured for TTL and CMOS-compatible logic thresholds. For TTL-compatible logic levels, the device will enable a data transmission when the input is driven 4.5 volts or higher, and the output will remain HIGH until the voltage falls below 3 volts. For CMOS-compatible logic levels, the data transmission will be enabled with a 1.8-volt input level, and the output won’t change until its voltage falls below 0.8 volts.

Finally, the 74AC646SC also includes a resonance circuit. This circuit is designed to reduce ringing and improve the rise and fall times of the output signals. This also reduces the propagation delay, increases noise margins and results in improved AC performance.

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