Hi Tan,
Please keep in mind that ASYS is a power pin for PCA9420, it is selected from VIN or VBAT and supply for the device internally. There is no spec on VSUS current capability, as when ASYS select VIN, VIN has current limit. What's more, BUCKs and LDOs supplied by ASYS all have current protection.
We do not recommend to use ASYS to power other loads, besides PCA9420 internal usage.
Best regards,
Tomas