4 Case Study

Take an example of an use case requiring 1.2V to 1.8V translation operating at 32Mbps. If we probe the output of device with a 20+ cable, the behavior can be seen similar to the Figure 4-1.

Figure 4-1 TXB0304, 1.2V to 1.8V Translation With Output Cabling of 20+ inch

As observed in Figure 4-1, the output (Teal) is unable to switch states due to the input (Dark Blue) toggling too fast. The result is the unwanted re-triggering of the one-shots at the input side when the output re-drives the incorrect/ delayed state back into the device due to the extrinsic delay from the 20+ in. cable. If a shorter cable is implemented, such as 4 in., the output signal is significantly improved as shown in Figure 4-2.

Figure 4-2 TXB0304, 1.2V to 1.8V Translation With Output Cabling of 9 in.

The output is now visible, though the overshoot % is high (44%), which can potentially damage downstream devices if unable to accept that voltage. Note the severe oscillations along the signal path, which is a result of impedance mismatch by the output driver of the TXB0304 facing external load. Again, the setup can be improved once more by reducing cable length and implementing series resistors at the outputs of the device. The final result after all adjustments can be shown in Figure 4-3.

Figure 4-3 TXB0304, 1.2V to 1.8V Translation With Output Cabling of 4 inch with Impedance Matched to Transmission Line Length