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USB Current & Voltage Droop and Drop Test Adapter

 

In-Rush Current/Voltage Droop & Drop Characteristics 

To prevent the possibility of damage to an upstream device, USB devices that are bus powered must implement 'In-Rush Current' limiting as defined in the USB 2.0 Specification - Chapter 7.  The profile of the In-Rush Current spike is restricted so the transient response of the power supply is not overwhelmed.  The rising edge of the current spike must be no more than 100 mA/ms. Downstream facing ports must be able to absorb the 500 mA peak current spike with a rising edge spike not faster than 100 mA/μs and meet the voltage droop requirements defined for in-rush current during dynamic attach.  Designers must also verify in-rush current when devices wakeup, either by themselves (remote wakeup) or when the device is signaled to resume.  The device must limit the In-Rush Current on VBUS.   

The 'Maximum Droop' on VBUS through the hub is 330 mV.  Additionally the device must have sufficient on-board bypass capacitance or a controlled power-on sequence such that the current drawn from the hub does not exceed the maximum current capability of the port at any time.  Bus powered hubs must have a VDROP of < 100 mV between upstream and downstream ports when 100 mA loads are present on all downstream ports.  Bus powered hubs with captive cables must have a VDROP of < 350 mV between upstream and all downstream ports including the cable.  

USBTestAdapter

 

 

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