2
AN1358.0
June 23, 2008
Power Supply
The DC power supply connected at banana jacks J2 (VDD)
and J1 (GND) provides power to the evaluation board. The
IC requires a +2.7V to +3.6VDC power supply for proper
operation. The power supply should be capable of delivering
100
µA
of current.
Logic Control
The state of the ISL54207 device is determined by the
voltage at the VBUS pin and the CTRL pin. Access to the
CTRL pin is through the banana jack J11 (CTRL) and access
to the VBUS pin is through the USB J4 connector or the
banana jack J3 (VBUS).
The CTRL logic control pin is 1.8V logic compatible which
allows for control via a standard
m
controller. In a typical
application, the VBUS logic control pin will be driven by the
VBUS
(4.4V to 5.25V) of the USB Host controller. An internal
4M
W
pull-down resistor on the IC will drive the logic low
when the pin is floating.
V
BUS
= Logic “0” (Low) when VBUS
≤
V
DD
+ 0.2V or
Floating.
VBUS = Logic “1” (High) when VBUS
≥
V
DD
+ 0.8V
CTRL = Logic “0” (Low) when
≤
0.5V or floating.
CTRL = Logic “1” (High) when
≥
1.4V
If V
BUS
is floating (no USB host controller connected at the
J4 connector) and CTRL is HIGH (J11 connected to J2) the
part will be in the Audio/Video mode. The audio/video
switches will be ON and the USB switches will be OFF.
There will be a low impedance path from VIDEO IN to
VIDEO OUT and from MONO AUDIO IN to MONO AUDIO
OUT.
If VBUS is driven HIGH and CTRL = X (don’t care) the part
will be in the USB mode. The USB switches will be ON and
the audio/video switches will be OFF. There will be a low
impedance path from USB TO DEVICE to USB TO HOST.
If VBUS = LOW and CTRL = LOW the part will be in the Low
Power mode. In Low Power mode all switches are OPEN
and the IC will draw around 1nA of current.
When the USB connector at J4 is not connected to a USB
port on a computer, the
4M
Ω
pull-down will pull the VBUS
pin LOW putting the ISL54207 in the Audio/Video mode or
Low Power mode depending on the condition of the CTRL
pin. When a connection to a computer USB host is present
on J4, the voltage at the VBUS pin will be driven to 5V and
the part will automatically go into the USB mode.
Audio/Video Inputs
The evaluation board has two audio/video inputs labeled
VIDEO IN (J13) and MONO AUDIO IN (J15). Each of these
inputs have a BNC connector (J14 and J16 respectively)
wired in parallel with the RCA connector. You can connect an
audio/video source or generator at either the BNC connector
or the RCA connector.
In a typical application the composite video output (NTSC or
PAL) and the mono audio output of the video source, (i.e.
TV, video MP3 Player, digital camera, cellphone, etc.), would
be connected to the RCA jacks J13 for video and J15 for
mono audio on the evaluation board.
Over a signal range of ±1V (0.707V
RMS
) these switches
have an extremely low r
ON
resistance variation (0.03
Ω
)
.
They can pass ground referenced audio/video signals up to
0.707V
RMS
with very low distortion and degradation. A
3V
P-P
signal is acceptable but performance will degrade.
The audio/video channels are AC coupled with 100µF
capacitors (C
3
and C
4
). These capacitors remove any DC
voltage from the audio/video signals and reference them to
ground of the device. If the audio/video source being
connected to the evaluation board already has internal
AC-coupling capacitors at the output of its drivers then the
capacitors on the evaluation board should be shorted out
(replaced with 0
Ω
resistors). This will prevent further
attenuation of the low frequency content of the audio signal
due to the increase of the high-pass corner frequency
resulting from the evaluation board capacitor in series with
the audio/video source capacitor.
Note: When in USB mode the audio/video source needs to
be in a high impedance state so it will not interfere with the
USB signal. Since the audio/video source inputs are
AC-coupled on the evaluation board, simply turning the
audio/video source OFF will isolate it from interfering with
the USB signal.
Audio/Video Outputs
The evaluation board has RCA type connectors labeled J5
and J7 for A/V output connections. For video playback, a TV
monitor should be connected at these connectors using a
standard A/V cable. The video input port of the TV should be
connected to VIDEO OUT (J5) and the audio input port of
the TV should be connected to MONO AUDIO OUT (J7).
The BNC connector J6 is in parallel with J5 and the D- line of
the J4 (USB TO HOST) connector. The BNC connector J8 is
in parallel with J7 and the D+ line of the J4 (USB TO HOST)
connector. These BNC connectors can be used to connect
resistive loads and/or test equipment to evaluate the
performance of the IC.
Note: When in USB mode, devices on the audio/video
outputs need to be in a high impedance state so it will not
interfere with the USB signal, since the USB and A/V
connections on the output/upstream side are all wired in
parallel.
USB Connections
A “B” type USB receptacle labeled “USB TO HOST” (J4) is
located on the left underside of the board. This receptacle
should be connected, using a standard USB cable, to the
up-stream USB host controller which is usually a PC
computer or hub. When this connection is made the
Application Note 1358
