Why all the VIN pins are separated in the ADP5034 and other uPMUs? Can I connect these all together to one capacitor?
The first advantage is to support different input supply voltages for Bucks and LDOs, it is very common for example to cascade one LDO from a buck to minimize the power losses although it is not recommended to have different input voltage levels for the bucks and should be supplied with the same supply level, in addition a LDO VIN cannot be higher than the bucks VIN.
Another important advantage of having separated VINs is to offer a better noise bypassing, each VIN can be connected to a dedicated input capacitor that should be placed as close as possible to the respective VIN, this is critical for the bucks. Even in case all regulators are supplied with the sample voltage it is not recommended to use only one capacitor connected to all VINs, the noise bypassing will not be good and the regulators operation may be affected.
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