Teledyne LeCroy QPHY-USB - Manual (Page 48)

48
QPHY-USB Operator’s Manual Rev F
Hub and Host Drop Test
Note: The drop test is performed using a voltmeter and the test fixture alone. The oscilloscope is not used for this test. The drop test is not
contained in the USB Test Wizard.
Set up the voltmeter to measure the voltage drop across the loads, as shown in the following figure. Attach all the
output ports of the hub or host to any of the loads on the Test Fixture. Make sure the three position switches on
each load are in the center (off) position before connecting the cables.
Note: The Upstream Port VBus voltage measurement (J23) is only required when testing Bus-powered Hubs.
Figure 51. Bus-Powered Hub Drop test equipment setup
Self-powered Hubs or Hosts
1. Switch the loads to the 500 mA position one at a time and verify that the voltage is between 4.75 and
5.25 V.
2. Repeat as necessary for all ports of the hub or host.
V
DROP
= V
NL
- V
LOADED
Where
V
NL
= V
BUS
at a downstream USB connector with USB ports open circuited (no load)
And
V
LOADED
= V
BUS
at a downstream USB connector with 100 or 500 mA loads, as appropriate, on all
USB ports