Installation Instructions

LISA-U2 series - System Integration Manual
UBX-13001118 - R19 Early Production Information System description
Page 77 of 175
External series resistors on pins USB_D+ and USB_D- as required by the Universal Serial Bus Revision 2.0
specification [7] are also integrated: characteristic impedance of USB_D+ and USB_D- lines is specified by the
USB standard. The most important parameter is the differential characteristic impedance (Z
0
) applicable for
odd-mode electromagnetic field, which should be as close as possible to 90  differential: signal integrity may
be degraded if the PCB layout is not optimal, especially when the USB signaling lines are very long. The common
mode characteristic impedance (Z
CM
) of each USB data line should be as close as possible to 30 .
LISA-U2 series
VBUS
D+
D-
GND
18
VUSB_DET
27
USB_D+
26
USB_D-
GND
C1
USB DEVICE
CONNECTOR
D1 D2 D3
Figure 40: USB Interface application circuit
Reference
Description
Part Number - Manufacturer
D1, D2, D3
Very Low Capacitance ESD Protection
PESD0402-140 - Tyco Electronics
C2
100 nF Capacitor Ceramic X7R 0402 10% 16 V
GRM155R61A104KA01 - Murata
Table 34: Component for USB application circuit
If the USB interface is not connected to the application processor, it is highly recommended to provide
direct access to the VUSB_DET, USB_D+, USB_D- lines for execution of firmware upgrade over USB
using the u-blox EasyFlash tool and for debug purpose: testpoints can be added on the lines to
accommodate the access. Otherwise, if the USB interface is connected to the application processor, it is
highly recommended to provide direct access to the RxD, TxD, CTS and RTS lines for execution of
firmware upgrade over UART and for debug purpose. In both cases, provide as well access to RESET_N
pin, or to the PWR_ON pin, or enable the DC supply connected to the VCC pin to start the module
firmware upgrade (see Firmware Update Application Note [17]).
If the USB interface is not used, the USB_D+, USB_D- and VUSB_DET pins can be left unconnected, but
it is highly recommended to provide direct access to the lines for FW upgrade and debug purpose.