Integration Manual

LISA-U2 series - System Integration Manual
UBX-13001118 - R25 System description Page 78 of 182
1.9.3.3 USB application circuit
Since the module acts as a USB device, the USB supply (5.0 V typ.) must be provided to VUSB_DET by
the connected USB host. The USB interface is enabled only when a valid voltage as a USB supply is
detected by the VUSB_DET input. 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 only a few
microamperes.
The USB_D+ and USB_D- lines carry the USB serial data and signaling. The lines are used in single-
ended mode for relatively low speed signaling handshaking, as well as in differential mode for fast
signaling and data transfer.
USB pull-up or pull-down resistors on pins USB_D+ and USB_D- as required by the Universal Serial Bus
Revision 2.0 specification [7] are part of the USB pad driver and do not need to be externally provided.
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 the 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 an 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 the firmware
upgrade over USB using the u-blox EasyFlash tool and for debugging purposes: 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 the firmware upgrade over UART and for debugging purposes. 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 the Firmware Update
Application Note [16]).
☞ 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 debugging purposes.