By Texas Instruments 60
Texas Instruments' SN74AXCH8T245 is an 8-bit, non-inverting, bus transceiver that resolves voltage level mismatch between devices operating at voltage nodes (0.7 V, 0.8 V, and 0.9 V) and devices operating at industry-standard voltage nodes (1.8 V, 2.5 V, and 3.3 V) and vice-versa. This device operates by using two independent power-supply rails, VCCA and VCCB. Data pins A1 through A8 track VCCA and accept any supply voltage from 0.65 V to 3.6 V. Data pins B1 through B8 track VCCB and accept any supply voltage from 0.65 V to 3.6 V. Additionally the SN74AXCH8T245 is compatible with a single-supply system.
The SN74AXCH8T245 offers asynchronous communication between data buses. This 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 (DIR1 and DIR2). The output-enable (OE) input disables the outputs so the buses are effectively isolated. The DIR and OE control pins are referenced to VCCA.
Unused or undriven inputs are held by active bus-hold circuitry at a valid logic state. It is not recommended to use the pull-up or pull-down resistors with the bus-hold circuitry. If a supply is present for VCCA or VCCB, the bus-hold circuitry always remains active on all A and B ports respectively, independent of the direction control or output enable. This device is fully specified for partial-power-down applications using Ioff, which disables the outputs when the device is powered down. This inhibits current backflow into the device which prevents damage to the device.
The VCC isolation feature ensures that if either VCC input supply is below 100 mV, all level shifter outputs are disabled and placed into a high-impedance state. The OE ties to VCCA through a pull-up resistor ensuring the high-impedance state of the level shifter I/Os during power-up or power-down. The minimum value of the resistor is determined by the current-sinking capability of the driver.