Search the Community
Showing results for tags 'usb2.0'.
Found 1 result
I've measured the Analog Discovery 2 drawing a current of 510 mA over USB. The USB 2.0 specification  dictates that devices shall not draw an absolute maximum current greater than 100 mA before configuration and shall not draw an absolute maximum current greater than 500 mA once configured. It appears to me that the AD2 is not compliant with the USB 2.0 specification. This could explain the Waveforms 2015 errors messages that I reported in another thread on this forum . Measurements were taken on a "warm" AD2 that had already been operating; I anticipate peak current on an AD2 that has been disconnected for some period will be higher (capacitances discharged). Measurements were performed with the AD2 running solely from USB power. Measurements were taken while connecting the AD2 to a PC on which the Waveforms 2015 software was already running. Measurements were not taking during AD2 acquisition or waveform generation operations. Didn't get a photo of the 510.1 mA measurement, but a photo of a 507.7 mA measurement is attached. The measurements were made with a Fluke 87V in mA DC mode with the range manually fixed to "600". The large currents were detected using peak-min-max mode (250 microsecond response time). The large currents were not detected using regular min-max mode (100 millisecond response time). The USB 2.0 spec makes the peripheral responsible for limiting its in-rush current and implementing soft-start as needed. -- Chris  http://www.usb.org/developers/docs/usb20_docs/usb_20_120516.zip --> usb_20.pdf, sections 7.2.1 and 188.8.131.52  https://forum.digilentinc.com/topic/3226-waveforms-2015-jtscinitscanchain-failed-error-dptiio-failed-error-ubuntu-16041-x86-64-analog-discovery-2-analog-discovery-2/#comment-11671