The Argon and Xenon don't sport a PMIC chip.
Here is the block diagram for the Boron
https://docs.particle.io/datasheets/cellular/boron-datasheet/#block-diagram
And here for the Xenon
https://docs.particle.io/datasheets/mesh/xenon-datasheet/#block-diagram
To know whether or not the LiPo is charging you can have a look at this discussion