[FAQ] TPS25947: How to achieve 3 channel Priority PMUX using TPS25947

TPS25947's provides a pin called "AUXOFF" (Auxiliary channel control signal). It is an open drain pin, and this can be used to enable/disable the auxiliary supply eFuse to facilitate smooth switchover in a Priority power MUXing configuration. The datasheet describes this in section 9.5 with some options based on system rail voltage or OVLO requirements. 

Example configuration for 2 channels from datasheet is as follows.

If the OVLO is not required, the AUXOFF pin can directly be connected to the OVLO of second channel to control the device. The OVLO acts similar to ENb pin so when the AUXOFF1 (first channel AUXOFF signal) is high the OVLO2 (second channel OVLO signal) will be high, and this will ensure the device remain off. When the eFuse1 turns off, the AUXOFF will go low, and this will turn on the eFuse2.

Similarly, if OVLO is required, we can use an external FET to either pull the EN low or pull the OVLO pin to high (if no external rails are present in the system, then pull to VIN rail if it is below 5V).

Now to extend this to three channels, we want eFuse3 to turn on only when both eFuse1 and eFuse2 are turned off so we cannot just use eFuse2 AUXOFF signal to control the eFuse3. We will have to use an external gate logic like OR gate for this. Here is an example implementation.

Here we have used an external FET to pull EN low to turn off the device and we have an external OR gate which ensures that both AUXOFF1 and AUXOFF2 are low before turning on the eFuse3.

Similar external logic can be used to create 4 channel Priority PMUX. 

Best Regards,
Arush