SN74AVC4T774

ACTIVE

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4-bit dual-supply bus transceiver with configurable voltage-level shifting and 3-state outputs

This 4-bit noninverting bus transceiver uses two separate configurable power-supply rails. The A port is designed to track V_CCA. V_CCA accepts any supply voltage from 1.2 V to 3.6 V. The B port is designed to track V_CCB. V_CCB accepts any supply voltage from 1.2 to 3.6 V. The SN74AVC4T774 is optimized to operate with V_CCA/V_CCB set at 1.4 V to 3.6 V. It is operational with V_CCA/V_CCB as low as 1.2 V. This allows for universal low-voltage bi-directional translation between any of the 1.2-V, 1.5-V, 1.8-V, 2.5-V, and 3.3-V voltage nodes.

The SN74AVC4T774 is designed for asynchronous communication between data buses. The logic levels of the direction-control (DIR) input and the output-enable (OE) input activate either the B-port outputs or the A-port outputs or place both output ports in the high-impedance mode. The device transmits data from the A bus to the B bus when the B outputs are activated, and from the B bus to the A bus when the A outputs are activated. The input circuitry on both A and B ports is always active and must have a logic HIGH or LOW level applied to prevent excess I_CC and I_CCZ.

The SN74AVC4T774 is designed so that the control pins (DIR1, DIR2, DIR3, DIR4, and OE) are supplied by V_CCA. This device is fully specified for partial-power-down applications using I_off. The I_off circuitry disables the outputs, preventing damaging current backflow through the device when it is powered down. The V_CC isolation feature ensures that if either V_CC input is at GND, then both ports are in the high-impedance state.

To ensure the high-impedance state during power-up or power-down, OE should be tied to V_CCA through a pullup resistor; the minimum value of the resistor is determined by the current-sinking capability of the driver. Since this device has CMOS inputs, it is very important to not allow them to float. If the inputs are not driven to either a high V_CC state, or a low-GND state, an undesirable larger than expected I_CC current may result. Since the input voltage settlement is governed by many factors (for example, capacitance, board-layout, package inductance, surrounding conditions, and so forth), ensuring that they these inputs are kept out of erroneous switching states and tying them to either a high or a low level minimizes the leakage-current.