10.1.2.2 Buffered Translators/Level-shifters

The TCA980x family supports connections with buffered translators, but care must be taken to ensure that no operating conditions be violated. In a general sense, the following must be avoided on the B-side ports of the TCA980x:

• Sources of current other than the individual TCA980x (B-side of the other TCA980x, external pull-up resistors, current sources, rise time accelerators, etc)
• Static-voltage offset buffer outputs (B-side of the TCA9517, etc)
• Outputs with R_ILC (equivalent pull-down resistance) > 150 Ω

It is important to note that these special operating requirements apply only to the B-side ports of the TCA980x. For example, the TCA9517 B-side can be safely connected to the A-side of the TCA980x, but not to the B-side of the TCA980x. However, it is OK to connect the A-side of the TCA9517 to the B-side (or A-side) of the TCA980x, because the A-side does not have a static voltage offset based output.

Figure 17 shows an example of the incorrect connection on the B-side to a buffer with a static voltage offset output. The reason this is unacceptable is because the equivalent output resistance of the output buffer is greater than the maximum R_ILC allowed. See the RILC section for more information.

Figure 17. Incorrect B-Side Static Voltage Offset Buffer Connection

Figure 18. Correct Connection With Other Buffers

As shown in Figure 18, this connection is acceptable for use on the B-side ports of the TCA980x, because the equivalent R_ILC of the A-side of this example buffer is less than 150 Ω.