Other Parts Discussed in Thread: TPS548B22, TPS548D22
Depending on the available supply, customers may ask if they can use PMBus parts such as the TPS549D22 or TPS549D22 in place of their pin-to-pin counterparts that lack a PMBus interface such as the TPS548D22 or TPS548B22. In this case, customers often do not have a means to drive the PMBus communication and prefer a drop-in replacement solution with bill of material (BOM) changes being the main option they are willing to explore. When doing this, it is perfectly acceptable to use a PMBus part in place of a non-PMBus part without PMBus communication so long as the default part parameters that are only accessible and/or programmable via PMBus are acceptable to for the application. These parameters contained in the part memory accessible via PMBus often include items such as compensation settings and switching frequency.
When the PMBus system is not in use, TI typically recommends grounding the PMBus connections (clock, data, and alert) such that any chance of noise entering the device through an unterminated pin is greatly reduced. However, if grounding the PMBus interface is not able to be accommodated, it is also acceptable to leave the PMBus pins floating. The part will then operate without external communication following the default programmed operating parameters contained within the part's memory. This offers the ability to drop in a pin-to-pin compatible PMBus part into a non-PMBus part footprint in cases such as swapping the TPS549D22 for the TPS548D22 without changing the PCB layout and only needing to accommodate minor do not populate changes in the bill of materials (BOM). Please note again that the default parameters only accessible via PMBus must be acceptable for the application in order for this to be an effective solution.