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USB2517: ESD protection and filtering

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Digitronic
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2020/06/03 03:21:51 (permalink)
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USB2517: ESD protection and filtering

Hi,
I was wondering if you could help me on this one.
I have an issue with a USB2517 USB hub on a board driven by an embedded PC: this EPC is here for 1/receiving the data from the USB peripherals and 2/check for the status with the board
My concern is the board' schematic is "partially" following evaluation module, with MIC2026 on each channel but also common mode chokes and ESD protection. This choke is a dedicated "USB 2.0 common mode choke", but I am not confident on this one; first, because it is not on the EVboard, then because when connecting a "high demanding" peripheral the 5V USB measured on the peripheral goes below 5V and the USB hub goes not responsive any more.
 
Any advices about the use of those chokes and ESD protection ?
Maybe the problem is elsewhere but I need to confirm...
 
Regards
 
 
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    roundrocktom
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    Re: USB2517: ESD protection and filtering 2020/06/04 09:41:29 (permalink)
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    It sounds like the device attached as a USB peripheral is pulling more than 500mA?
     
    USB valid voltage is 5V +-5%; or 4.75V to 5.25V
     
    A MIC2026 will deliver about 700mA before it shuts down and flips the overcurrent flag.
     
    It is the Operating System (OS) that takes the information about an overcurrent and tell the hub then to shut down port power. Some OS will automatically re-enable port power, others won't.  Just don't overlook the OS needs to be running and is control of port power, not the hub.
     
    Check your power supply current? Do you need a larger supply?
     
    Is the problem too small of a trace on your board to the 5V rail to USB connectors?
     
    If you have externally connected ports, I add the chokes and ESD protection.   Here in Texas I never see issues (too humid) but boards that went to Alberta, Canada every winter due to dry air and seeing 15KV ESD, they are needed.
     
    If you need to supply 1A, take a look at the MIC2040
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    Digitronic
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    Re: USB2517: ESD protection and filtering 2020/06/05 01:00:28 (permalink)
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    Hi @roundrocktom,
     
    Thanks for your feedback.
    The device I connect is a smartphone, pretty sure it -can- drain more than 500mA.
    Maybe my understanding of USB protocol need some investigation but here's what I thought: on connection, during the enumeration and negociation, the device is considered as low power or high power, thus providing 100mA or 500mA. Based on this assumption, the device could not drain more than 500mA. Am I wrong with this ?
    I made a test with the USB2517 EVboard and a Klein Tools ET910 (not the most accurate, but for a test I guess it is OK)
    - loading one port with a test load to drain 500mA, the current drained is about 460mA and oother ports are still available and usable
    - loading one port with the very same cable and smartphone, the current drained is about 430mAand other ports are still available and usable
     
    About the OS, on Windows 10, I have noticed something: on the device I am reviewing, when the USB hub goes down, even resetting the hub doesn't make it back "alive": it appears as "other device" with a yellow interrogation mark. Unable to test it on Linux but it seems Windows is unable to re-enable the port.
     
    For the choke and ESD protection, it is then good practices
     
    Regards
     
    #3
    roundrocktom
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    Re: USB2517: ESD protection and filtering 2020/06/05 06:27:12 (permalink)
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    When a device is enumerated, it should only consume 100mA. During that time it tells the host "hey I will need 300mA" when attached. Once attached 500mA is allowed.
     
    The host will total up what has been connected to the hub and reported to it. The HOST OS knows it shouldn't exceed 500mA for HUB & Attached devices when BUS POWERED.
     
    If you have the HUB report back it is SELF POWERED (i.e. a wall power supply is powering is up) the Host isn't concerned with power being reported with devices being attached.
     
    There are no power measurements taking place, only what is being reported.
     
    How is the device configured?  If you could post up a PDF link to the HUB schematic.  Hubs can be set by pin configuration, separate EEPROM, or having the host processor set via SMBus.
     
    There are some Tools to show what enumerated and details.  
     
    https://docs.microsoft.com/en-us/windows-hardware/drivers/usbcon/capture-and-view-ing-usb-traces-with-microsoft-message-analyzer-
     
    If it enumerated, and you have VALID VID and PID then time to look at pin configurations. Yellow Bang could be the device is reporting compound (always attached) devices and Bus-powered but reporting it needs 900mA the Host will just say NO  and not connect, blocking the device.
     
    If there is a problem with VID AND PID we know the issue is between the HOST and HUB. On a single board, those should be straight lines. A caveat is any capacitance over 3pf will let FS (12MHz) communication, but blocks HS (480Mhz) communication.
     
     
     
     
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