Automotive bus transceiver provides configurable voltage-level shifting and bus hold

18-03-2024 | Texas Instruments | Power

This Texas Instruments' 4-bit noninverting bus transceiver employs two separate configurable power-supply rails. The A port is designed to track VCCA. VCCA accepts any supply voltage from 1.08V to 3.6V. The B port is designed to track VCCB. VCCB accepts any supply voltage from 1.08V to 3.6V. The SN74AVCH4T245-Q1 is optimised to operate with VCCA/VCCB set at 1.08V to 3.6V. It is operational with VCCA/VCCB as low as 1.08V. This provides for universal low-voltage bidirectional translation between any of the 1.2V, 1.5V, 1.8V, 2.5V, and 3.3V voltage nodes.

The device is designed for asynchronous communication between two 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 into the high-impedance mode. The device transmits data from the A bus to the B bus when the B-port outputs are activated and from the B bus to the A bus when the A-port outputs are activated. The input circuitry on both A and B ports is always active and must apply a logic HIGH or LOW level to prevent excess ICC and ICCZ.

The device control pins (1DIR, 2DIR, 1OE, and 2OE) are supplied by VCCA.

This device is fully specified for partial-power-down applications employing Ioff. The Ioff circuitry disables the outputs, stopping damaging current backflow through the device when powered down.

The VCC isolation feature is designed so that if either VCC input is at GND, then both ports 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 data inputs at a valid logic state. Pull-up or pull-down resistors are not recommended with this circuitry, which always stays active on the powered-up side.

To put the device in the high-impedance state through power up or power down, tie the OE pin to VCC through a pull-up resistor; the driver's current-sinking capability determines the resistor's minimum value.

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By Seb Springall