Usb Interface - u-blox LISA-C2 Series System Integration Manual

Any external signal connected to the UART interface must be tri-stated when the module is in power-down
mode, when the external reset is forced low and during the module power-on sequence (at least for 3 s
after the start-up event), to avoid latch-up of circuits and allow a proper boot of the module. If the external
signals connected to the cellular module cannot be tri-stated, insert a multi channel digital switch (e.g.
Texas Instruments SN74CB3Q16244, TS5A3159, or TS5A63157) between the two-circuit connections and
set to high impedance during module power down mode, when external reset is forced low and during
power-on sequence.
LISA-C200 modules require special attention when used with voltage level shifter connections.
V_INT (1.8V) is provided to support biasing of level shifter ASICs. A problem can result with
certain level shifter interface buffers, which can back feed voltage to the V_INT line preventing
the modem from powering off and/or resetting properly. The back feed voltage typically comes
from host output through the level shifter: either from the level shifter VCC pin connected to
V_INT, or to the modem TxD input lines though an internal protection diode with modem. With
modem VCC = 0 V, a measured voltage can range from 0.3 to 1.0 V on the V_INT, preventing the
modem from ever resetting or powering up or down properly.

1.9.3 USB interface

LISA-C200 and FW75-C200 modules provide a full-speed USB interface at 12 Mb/s compliant with the Universal
Serial Bus Revision 2.0 specification [10]. It acts as a USB device and can be connected to any USB host such as a
PC or other Application Processor.
The USB-device looks for all upper-SW-layers like any other serial device. This means that LISA-C200 and FW75-
C200 modules emulate all serial control logical lines.
If the logical DTR line isn't enabled by the USB host, the module doesn't answer to AT commands by the
USB interface.
Name Description
VUSB_DET USB detect input
USB_D+ USB Data Line D+
USB_D- USB Data Line D-
Table 15: USB pins
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 on the application board.
Higher protection level 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.
UBX-13000620 - R21
LISA-C2 series and FW75-C200 - System Integration Manual
Remarks
Apply 5 V typical to enable USB
90 Ω nominal differential impedance.
Pull-up or pull-down resistors and external series resistors as
required by the USB 2.0 high-speed specification [10] are
part of the USB pad driver and need not be provided
externally.
90 Ω nominal differential impedance.
Pull-up or pull-down resistors and external series resistors as
required by the USB 2.0 high-speed specification [10] are
part of the USB pad driver and need not be provided
externally.
Early Production Information System description
Page 31 of 103