CCS/AM3352: USB VBUS error

Part Number: AM3352

Tool/software: Code Composer Studio

Hi.

I use board with custom hardware, that connect WiFi over USB to am3352. I use mainline Linux 4.8.17. 

In my board schematics only USB signal lines (USB1_DM and USB1_DP) connected from CPU to WiFI (but not USB Power line, USB +5V connected from other power supply, and not connected with am3352).

In result I see USB error in dmesg:

[  734.531123] musb-hdrc musb-hdrc.0.auto: VBUS_ERROR in a_wait_vrise (81, <SessEnd), retry #1, port1 0008050c
[  734.683550] musb-hdrc musb-hdrc.0.auto: VBUS_ERROR in a_wait_vrise (81, <SessEnd), retry #2, port1 0008050c
[  734.835977] musb-hdrc musb-hdrc.0.auto: VBUS_ERROR in a_wait_vrise (81, <SessEnd), retry #3, port1 0008050c
[  734.988398] musb-hdrc musb-hdrc.0.auto: VBUS_ERROR in a_wait_vrise (80, <SessEnd), retry #3, port1 0008050c

And USB does not work.

lsusb just show internal hub:

# lsusb  
Bus 001 Device 001: ID 1d6b:0002

My device tree (USB part):

&usb1_phy {

    status = "okay";

};

&usb1 {

    status = "okay";

    dr_mode = "host";

};

&cppi41dma {

    status = "okay";

};

i know that USBx_VBUSIN pin should be connected to Valid VBus of >=4.4V, when the musb is configured as usb host, otherwise you will get bus error.

But measured  vbus voltage is 4.96V by oscilloscope,it have more than 4.4V.

Now i start to doubt its cause is not hardware.

1.do you think if its cause is software or not ？

2. NCP380 is related to VBUS error or not ?

3.what is root cause ?

4.How I can fix USB?