The SN74CBTD3305C is a high-speed TTL-compatible FET bus switch with low ON-state resistance (ron), allowing for minimal propagation delay. This device features an integrated diode in series with VCC to provide level shifting for 5-V input down to 3.3-V output levels. Active Undershoot-Protection Circuitry on the A and B ports of the SN74CBTD3305C provides protection for undershoot up to 2 V by sensing an undershoot event and ensuring that the switch remains in the proper OFF state.
The SN74CBTD3305C is organized as two 1-bit bus switches with separate output-enable (1OE, 2OE) inputs. It can be used as two 1-bit bus switches or as one 2-bit bus switch. When OE is high, the associated 1-bit bus switch is ON, and the A port is connected to the B port, allowing bidirectional data flow between ports. When OE is low, the associated 1-bit bus switch is OFF, and a high-impedance state exists between the A and B ports.
This device is fully specified for partial-power-down applications using Ioff. The Ioff feature ensures that damaging current will not backflow through the device when it is powered down.
To ensure the high-impedance state during power up or power down, OE should be tied to GND through a pulldown resistor; the minimum value of the resistor is determined by the current-sourcing capability of the driver.