9.1 Application Information

The SN74LVCH245A device is a high-drive CMOS device with bus-hold inputs that can be used for a multitude of bus interface type applications where the data needs to be transmitted and received. The device's output can produce 24 mA of drive current at 3.3 V. Therefore, this device is ideal for driving multiple outputs and for high-speed applications up to 100 MHz. The inputs are 5.5-V tolerant which allows the devices to translate down to V_CC.

Figure 10 shows a typical down-translation application in which the device is being used with a fixed direction to reduce an 8-bit 5-V bus to an 8-bit 1.8-V bus.

Figure 11 shows a typical application in which a bus must switch directions for data transfer between a master and a slave device. The SN74LVCH245A allows either V_CC1 or V_CC3 to be shut down completely because it has bus-hold inputs that maintains valid states on the floating lines. In this example, V_CC1, V_CC2, and V_CC3 all have the same value, but each supply can be delivered by a separate source.

Figure 12 shows a functional diagram for a single channel of the device, including the bus-hold, direction, and output enable logic components. When the direction is set as 'A to B,' the buffer labeled 'A' is disabled and the buffer labeled 'B' is enabled. When the direction is set as 'B to A,' the buffer labeled 'B' is disabled and the buffer labeled 'A' is enabled. When the output enable pin is deasserted, the buffers labeled 'A' and 'B' are both disabled. The bus-hold circuitry remains active at all times.