This 20-bit noninverting bus transceiver uses two separate configurable power-supply rails. The SN74AVCH20T245 is optimized to operate with VCCA/VCCB set at 1.4 V to 3.6 V. It is operational with VCCA/VCCB as low as 1.2 V. The A port is designed to track VCCA. VCCA accepts any supply voltage from 1.2 V to 3.6 V. The B port is designed to track VCCB. VCCB accepts any supply voltage from 1.2 V to 3.6 V. This allows for universal low-voltage bidirectional translation between any of the 1.2-V, 1.5-V, 1.8-V, 2.5-V, and 3.3-V voltage nodes.
The SN74AVCH20T245 is designed for asynchronous communication between data buses. The device transmits data from the A bus to the B bus or from the B bus to the A bus, depending on the logic level at the direction-control (DIR) input. The output-enable (OE)\ input can be used to disable the outputs so that the buses are effectively isolated.
The SN74AVCH20T245 is designed so that the control (1DIR, 2DIR, 1OE\, and 2OE\) inputs are supplied by VCCA.
This device is fully specified for partial-power-down applications using Ioff. The Ioff circuitry disables the outputs, preventing damaging current backflow through the device when it is powered down.
The VCC isolation feature ensures that if either VCC input is at GND, both outputs are in the high-impedance state. The bus-hold circuitry on the powered-up side always stays active.
Active bus-hold circuitry holds unused or undriven inputs at a valid logic state. Use of pullup or pulldown resistors with the bus-hold circuitry is not recommended.
To ensure the high-impedance state during power up or power down, OE\ should be tied to VCC through a pullup resistor; the minimum value of the resistor is determined by the current-sinking capability of the driver.