5
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AN1408.0
February 13, 2009
6. You can observe the D- and D+ USB digital signals on an
oscilloscope or other test equipment by connecting to the
J8, J14, J9 and J15 BNC connectors or various test
points located on the board (see Test Points page 5).
7. Remove the 0
Ω
resistors R1, R2, R3, R4 when
evaluating the signal quality (i.e. eye diagram, etc.) of the
high speed USB signal. Removal of these resistors
disconnects the headphone jack (J7) and BNC
connectors (J8, J9, J14, J15) from the USB differential
lines. These components when connected will degrade
the USB signal. These components will not be there in an
actual application.
If you disconnect the USB cable from J1 and take the IN pin
LOW, the IC will return to Audio mode. You can now plug the
headphone set into headphone jack, turn the audio source
ON to once again play music.
Test Points
The board has various test points for ease of connecting
probes to make measurements. The test points available are
described in Table 2.
TABLE 2.
DESIGNATOR
DESCRIPTION
TP1
V
DD
Test Point
TP2
Ground Test Point
TP3
V
BUS
Test Point
TP4
Audio Left Input Test Point
TP5
Audio Right Input Test Point
JP1
D-/D+ Differential Probe Connection - USB Device
Side of Switch
JP2
D-/D+ Differential Probe Connection - COM Side of
Switch
Application Note 1408
