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

-

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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

Parents
  • +1
    •  Analog Employees 
    on Feb 1, 2021 11:15 AM 2 months ago

    Hi Ken,

    DD- is high in your screenshot above, suggesting the keyboard is presenting as low-speed (pulling DD- high).

    If the keyboard itself is a low speed device, then you will need to pull SPU and SPD low, as well as removing the 10k pull-up on D+ (if it is low speed, the keyboard will have the appropriate pull-up on DD-, but the ADuM3160 needs to match this on UD-, not just the logic state). If the ADuM3160 has SPU and SPD low, with PIN pulled high, then once a pull-up applies to DD-, power will be applied to UD- pull-up to reflect the keyboard being attached.

    If you are intending to support both low and full speed with the isolation circuit, we can recommend LTM2894, which has automatic speed selection built-in (although it's larger for a very high isolation rating).

    Best regards,

    Conal

  • Hi Conal

    thanks for your prompt reply, after changing to a USB device like  FTDI FT232  USB to UART transceiver which works on full speed, the isolated communication worked fine.

    I have another question about USB hub in CN-0158

    First, This  is my simplified signal chain for your reference

     USB contoller inside intel CPU <--> ADUM3160 <--> USB Hub <---> USB device 

    Note: CPU, ADUM3160, USB hub USB2512 are all located at my designed PCB, the product is an IPC

     https://www.mouser.tw/datasheet/2/268/00001692B-767361.pdf

    please correct me if my understanding about the function of the USB hub is wrong.

    since the USB device can be full or low speed one

    The USB hub controller USB2512 is used to adapt to the correct speed of the device

    at the mean time, it can communicate with CPU with ADUM3160 at fixed speed (e.g. full speed)

    in this scenario, the Hub is necessary even I just need a single isolated USB port, isn't it?

    thanks

    Ken

  • +2
    •  Analog Employees 
    on Feb 3, 2021 11:36 AM 2 months ago in reply to Kencheng

    Hi Ken,

    That's right, CN0158 is used to show how ADuM4160 can be used for isolation with ports that connect to low or full speed devices (the downstream ports). The hub is needed for this approach even if only one port is desired. As well as the LTM2894 supporting automatic low/full speed isolation, the LTM2884 is another option that includes an isolated DC-DC.

    Best regards,

    Conal

Reply
  • +2
    •  Analog Employees 
    on Feb 3, 2021 11:36 AM 2 months ago in reply to Kencheng

    Hi Ken,

    That's right, CN0158 is used to show how ADuM4160 can be used for isolation with ports that connect to low or full speed devices (the downstream ports). The hub is needed for this approach even if only one port is desired. As well as the LTM2894 supporting automatic low/full speed isolation, the LTM2884 is another option that includes an isolated DC-DC.

    Best regards,

    Conal

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