[christianw.]

5V0 at VCHG is fine (up to 6.5V). There's a datasheet available here:

https://www.tinyosshop.com/datasheet/CSR...0Sheet.pdf

I suspect a misconfigured CHRG-Setup as it is possible use the Chip with an external transistor as pass element for the charging to keep power-dissipation at the QFN-package low.

Have a look at page 65ff.