Ublox SARA-N4 Series, System Integration Manual

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SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R11 Design-in Page 105 of 157
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 [4] 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 SARA-R4/N4 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 48
and Table 33 .
☞
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.
D+
D-
GND
29 USB_D+
28
USB_D-
GND
USB DEVICE
CONNECTOR
VBUS
D+
D-
GND
29 USB_D+
28
USB_D-
GND
USB HOST
PROCESSOR
SARA-R4/ N4 SARA-R4/ N4
VBUS 17 VUSB_DET 17 VUSB_DET
D1 D2 D3
C1 C1
0 Ω
Test -Point
0 Ω
Test -Point
0 Ω
Test -Point
Figure 48: 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 33: Components for USB application circuits