Technical data

178 Notes on USB Electrical Compliance Testing
7 Low and Full Speed Tests
Droop/Drop Test
The Drop test is a measure of a hub’s ability to host full load current
while keeping the output voltage above spec. To perform this test, V
BUS
is
measured with all downstream ports loaded with 500 mA loads (for host
and self powered hubs) or 100 mA loads (for bus powered hubs). The
lowest value measured across all ports must be between 4.75 V and 5.25 V
for host and self powered hubs or it must be greater than or equal to 4.4
V for bus powered hubs.
The Droop test is a transient test on adjacent ports. When a device is hot
plugged into another port, the droop in V
BUS
supplied to a port must be
less than or equal to 220 mV for host, self powered, and bus powered
hubs.
New E2649-66405 Droop/Drop Test Fixture
Below is a picture of the new E2649- 66405 Droop/Drop test fixture along
with labels for each of its main components.
To begin, plug the USB cable from your oscilloscope into the USB Power
port to power the test fixture. The DS1 LED should illuminate (green
LED). See the picture below for the location of DS1 (the picture is zoomed
in on the upper left hand corner of the test fixture).
S1 Switch
S2 switch
Test
Ports
Loads
100mA Top surface
500mA bottom
Test port
indicator
Drop/droop
switch
100mA/500mA
switch
USB Power port
Droop test port Main Test
port