By Texas Instruments 26
Texas Instruments' SN74AXC4T245 4-bit, noninverting bus transceiver utilizes two individually-configurable power-supply rails and is operational with VCCA and VCCB supplies as low as 0.65 V. The A-port is designed to track VCCA, which accepts any supply voltage from 0.65 V to 3.6 V. The B-port is designed to track VCCB which accepts any supply voltage from 0.65 V to 3.6 V. The transceiver device is compatible with a single-supply system.
The SN74AXC4T245 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 of the direction-control inputs (1DIR and 2DIR). The output-enable inputs (1OE and 2OE) are used to disable the outputs so the buses are effectively isolated. The SN74AXC4T245 device is designed so the control pins (xDIR and xOE) are referenced to VCCA. To ensure the high-impedance state of the level shifter I/Os during power-up or power-down, the xOE pins should be tied to VCCA through a pull-up resistor.
The device is fully specified for partial-power-down applications using the Ioffcurrent. The Ioff protection circuitry ensures that no excessive current is drawn from or to an input, output, or combined I/O that is biased to a specific voltage while the device is powered-down. The VCC isolation feature ensures that if either VCCA or VCCB is less than 100 mV, both I/O ports enter a high-impedance state by disabling their outputs.
Glitch-free power supply sequencing allows either supply rail to be powered-on or -off in any order while providing robust power sequencing performance.