User's Manual

LE920 Hardware User Guide
1vv0301026 Rev.8 2015-01-03
Reproduction forbidden without written authorization from Telit Communications S.p.A. - All Rights
Reserved. Page 52 of 88
8. USB Port
The LE920 module includes a Universal Serial Bus (USB) transceiver, which operates at
USB high-speed (480Mbits/sec). It can also work with USB full-speed (12Mbits/sec) hosts
It is compliant with the USB 2.0 specification and can be used control and data transfers as
well as for diagnostic monitoring and firmware update. In fact firmware update by the host is
only possible via USB and not possible via UART. The reason is that Telit consider it
impractical to transfer firmware binaries exceeding 100Mb via UART.
The USB port on the Telit LE920 is typically the main interface between the module and
OEM hardware.
The USB_DPLUS and USB_DMINUS signals have a clock rate of 480MHz. The signal traces
should be routed carefully. Trace lengths, number of vias and capacitive loading should be
minimized. The impedance value should be as close as possible to 90 Ohms differential.
The table below describes the USB interface signals:
NOTE:
- USB_VBUS input power is internally used to detect the USB port and start enumeration
process. It isn’t used for supplying internal LE920 USB HW block. Therefore, only
maximum of 5mA is required.
- The USB_VBUS is internally pulled-down by 10k ohm resistor. Customer host
application must take into account voltage divider with the internal pull down resistor
meeting the minimum of 2.2V input, in case that a serial resistor is placed on
USB_VBUS signal.
NOTE:
In the case of not using USB communication, it is still highly recommended to place an
optional USB connector in the application board.
USB physical communication is needed in the case of SW update
Signal
LE920
Pad No.
Usage
USB_VBUS
A18
Power sense for the internal USB transceiver.
Acceptable input voltage range 2.2V 5.25V @ max 5mA consumption
USB_D-
F19
Minus (-) line of the differential, bi-directional USB signal to/from the
peripheral device
USB D+
D19
Plus (+) line of the differential, bi-directional USB signal to/from the
peripheral device