Teledyne LeCroy QPHY-USB - Manual (Page 51)

QPHY-USB Software Option
QPHY-USB Operator’s Manual Rev F
51
Remaining Loads are connected to the remaining downstream ports.
Test Steps
1. Select Host or Hub in the Mode control and Droop in the Test control of the USB Test Wizard. Follow the
instructions in the test wizard to acquire the droop waveform as shown:
Figure 54. Droop voltage waveform
2. Connect port 1 (port under test) of the hub or host under test to the Trigger section B socket (J25) of the
Test Fixture using a short cable. Connect the A socket (J27) of the Trigger section to load 1 (J8) of the
fixture using a 1 meter (3 ft.) USB cable. Connect port 2 of the hub or host under test to the droop section
of the Test Fixture (J1) using a 1 meter (3 ft.) USB cable. Connect the remaining ports of the hub or host
under test to the any of the remaining loads of the Test Fixture using 1 meter (3 ft.) USB cables. All
hub/host ports should have a load attached. Make sure all of the switches are in the center (OFF) position
before connecting the cables.
3. Connect channel 2 of the oscilloscope to J3 in the droop section of the fixture. Connect channel 3 of the
oscilloscope to J28 in the Trigger section of the fixture.
4. Switch all test loads to the appropriate current level (100 mA or 500 mA) as indicated in the table in the
Test Results section as follows.
Test Criteria
Section 7.2.4.1 of the USB 1.1 specification allows a maximum droop of 330 mV in the V
BUS
supplied to a USB
port when a device is hot plugged into another port. Droop testing evaluates worst-case droop by applying a 100
mA load and 10 µF of capacitance, which switches on and off to one of the adjacent available ports when all other
ports are supplying the maximum load possible. All V
BUS
measurements are relative to local ground.