9.2.2 Bidirectional Blocking and Protection of C

The TPS2410 and TPS2411 may be used in applications where bidirectional blocking is desired. This may occur in situations where two different voltages are ORed together, and operation from the lower voltage is desired. Another important application allows isolation of a redundant unit that is generating too high an output voltage. There are two considerations, first is the selection of the V_DD source, and second is protection of the C pin from excessive current. Figure 13 provides an example of this type of application.

V_DD needs to have voltage applied when A is to be connected to the load. Connecting V_DD to C only works when voltage on C is always present before A is connected. V_DD may be connected to A, a separate supply, or have voltage from A ORed with voltage from C. OV may be used to force GATE low, even when V_(A) is greater than V_(C), by driving OV to a voltage between 0.6 V and less than 5.25 V.

The C pin must be protected from excessive current if V_(A) can exceed V_(C) by more than 5.5 V. With a single MOSFET, V_(C) is never more than a diode drop lower than V_(A). When V_(AC) is greater than a diode drop, a small current flows out of the C pin into the load. If V_(AC) exceeds 5.5 V, a current limiting circuit should be used to protect C. Figure 13 provides an example circuit. Inserting this protection circuit creates a small offset in the forward regulation and threshold voltage.

Figure 13. Bidirectional Blocking Example