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ADUM3160 communication failed issue

Hi ADIexpert

I use ADUM3160 to isolate USB data from my CPU to external USB device (in my test, it's a keyboard)

please see my  test circuit and configuration below

-

---------------------

upstream

VBUS1: 5V

VDD1/PDEN/SPU: 3.3V

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douwnstream:

Vbus2/VDD2/SPD/PIN: 3.3V

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Also, I added a 10k pull up resisitor to Vbus2 at DD+ ( the idea is from  the issues on EZ zone )

but the communication is still failed

This is my test waveforms

1. the waveform when keyboard is attached to the USB port  (power on)

2. In win10, I rescan the USB device to try to make communication between host and device 

but it looked like the UD- can't pull low under VIL of ADUM3160

I tried to remove the isolator, the signal UD- can pull low to around 0V and the keyboard device was successfully detected in Win10 

any idea about the issue is appreciated

thank you

Ken