LARA-R2 series - System Integration Manual
UBX-16010573 - R02
Objective Specification
Design-in
Page 105 of 148
2.6.2
USB interface
2.6.2.1
Guidelines for USB circuit design
The
USB_D+
and
USB_D-
lines carry the USB serial data and signaling. The lines are used in single ended mode
for full speed signaling handshake, as well as in differential mode for high speed signaling and data transfer.
USB pull-up or pull-down resistors and external series resistors on
USB_D+
and
USB_D-
lines as required by the
USB 2.0 specification
are part of the module USB pins driver and do not need to be externally provided.
The USB interface of the module is enabled only if a valid voltage is detected by the
VUSB_DET
input (see the
LARA-R2 series
Data Sheet
[1]). Neither the USB interface, nor the whole module is supplied by the
VUSB_DET
input: the
VUSB_DET
senses the USB supply voltage and absorbs few microamperes.
Routing the USB pins to a connector, they will be externally accessible on the application device. According to
EMC/ESD requirements of the application, an additional ESD protection device with very low capacitance should
be provided close to accessible point on the line connected to this pin, as described in Figure 56 and Table 43.
The USB interface pins ESD sensitivity rating is 1 kV (Human Body Model according to JESD22-A114F).
Higher protection level could be required if the lines are externally accessible and it can be achieved by
mounting a very low capacitance (i.e. less or equal to 1 pF) ESD protection (e.g. Tyco Electronics
PESD0402-140 ESD protection device) on the lines connected to these pins, close to accessible points.
The USB pins of the modules can be directly connected to the USB host application processor without additional
ESD protections if they are not externally accessible or according to EMC/ESD requirements.
LARA-R2 series
D+
D-
GND
29
USB_D+
28
USB_D-
GND
USB DEVICE
CONNECTOR
D1 D2
VBUS
LARA-R2 series
D+
D-
GND
29
USB_D+
28
USB_D-
GND
USB HOST
PROCESSOR
C1
17
VUSB_DET
C1
17
VUSB_DET
VBUS
D3
Figure 56: USB Interface application circuits
Reference
Description
Part Number - Manufacturer
C1
100 nF Capacitor Ceramic X7R 0402 10% 16 V
GRM155R61A104KA01 - Murata
D1, D2, D3
Very Low Capacitance ESD Protection
PESD0402-140 - Tyco Electronics
Table 43: Component for USB application circuits
If the USB interface pins are not used, they can be left unconnected on the application board, but it is
recommended providing accessible test points directly connected to
VUSB_DET
,
USB_D+
,
USB_D-
pins.
