ASUS Fonepad 7 and OTG + charging

Hello,

I'm new here and I'm struggling about this problem:

I need to use and OTG cable and in the same time charge the device.
I bought an OTG + Charging cable, but the device is not charging (but otg function is ok).

I'm wondering if I need a custom firmware or a patch to get it working.

Thank you.
Marco.