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Apalis Carrier Board Design Guide
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2.5.2
Reference Schematics
As the additional SuperSpeed USB 3.0 data signals are PCIe Gen2 signals at the physical layer, the
schematic requirements are similar to those for PCIe. This means AC coupling capacitors are
required. The placement of the capacitors depends on whether the USB 3.0 device is populated on
the carrier board (device-down) or is connected over a cable. The USB 2.0 data signals do not
need any coupling capacitors.
The SuperSpeed interface consists of a pair of transmitting (TX) and receiving (RX) traces.
Unfortunately, the names RX and TX can be confusing as the host transmitter needs to be
connected to the receiver of the device and vice versa. Normally, the signals are named after the
host until they reach the pins of the USB device. Therefore, the transmitting pins on the Apalis
module should be called TX on the carrier board while the receiving pins should be called RX.
Please read carefully the datasheet of the USB device (device-down) in order to ensure RX and TX
are not confused.
2.5.2.1
USB 3.0 OTG Schematic Example
The AC coupling capacitors for the SuperSpeed TX signals are located on the Apalis module while
the capacitors for the RX signals are located on the USB device. No additional series capacitors are
required nor permitted on the Carrier board. The USB 2.0 data signals do not need any series
capacitors at all.
If the USB signals are externally available, ESD protection diodes need to be placed on all of the
USB signals. Make sure that the protection diodes are USB 3.0 compliant. The USB 2.0 signals
additionally require a common mode choke for passing EMI testing. Use common mode chokes
that are specified for High-speed USB 2.0.
Figure 20: USB 3.0 OTG Block Diagram
The USBO1_ID signal is used to detect which type of USB connector is plugged into the OTG jack
(Micro-AB jack). When a Micro-A connector is inserted, the ID pin is connected to signal ground,
causing the OTG port to be configured as a host. If a Micro-B USB connector is inserted, the ID pin
is left unbiased and the OTG port will be configured as a slave device. For the USBO1_ID signal a
pull-up resistor to 3.3V is needed.
The USBO1_VBUS input signal is only used if the OTG port is in client mode (Micro-B USB
connector plugged in or by software configured as slave only). The signal is used to detect whether
a host is connected on the other end of the USB cable. This signal is 5V tolerant and can be
connected directly to the power supply pin of the USB jack. ESD protection diodes should be used
for this signal.
Apalis Module
Carrier Board
TX
RX
RX
TX
USB
USBO1_SSTX-
USB
USBO1_SSRX-
USB
USBO1_SSTX-
USB
USBO1_SSRX-
2x 100nF
2x 100nF
SSTX+
SSTX-
SSRX+
SSRX-
USBO1_D-
USBO1_D-
RX/TX
U
SB
3
.0
O
TG
C
o
n
tr
o
lle
r
Super
Speed
USB 2.0/1.1
M
o
d
u
le
C
o
n
n
e
ct
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r
U
SB
3
.0
O
TG
C
o
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n
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ct
o
r
D+
D-
U
SB
3
.0
D
e
vi
ce
Super
Speed
USB 2.0/1.1
RX/TX
U
SB
3
.0
C
o
n
n
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ct
o
r
USB Drive
USB Cable
TVS
Diode
TVS
Diode
TVS
Diode