User's Guide

LM940 HW Design Guide
1VV0301352 Rev. 2 Page 37 of 68 2017-07-19
Information – Do not use any pull-up resistor on the RESET_N line or
any totem pole digital output. Using a pull-up resistor may cause latch-
up problems on the LM940 power regulator and improper functioning
of the module. The RESET_N line must be connected only in an open-
collector configuration.
Communication ports
Below table summarizes all the hardware interfaces of the LM940 module.
LM940 Hardware Interfaces
6.5.1. USB Interface
The LM940 module includes super-speed USB3.0 with high-speed USB2.0 backward
compatibility. It is compliant with Universal Serial Bus Specification, Revision 3.0 and can
be used for control and data transfers as well as for diagnostic monitoring and firmware
update.
The USB port is typically the main interface between the LM940 module and OEM
hardware.
USB 3.0 needs series capacitors on the TX lines in both directions for AC coupling. In
order to interface USB3.0 with an application board of customer, 0.1uF capacitors should
be installed on USB_SS_RX_P/M lines of the LM940. There are already series capacitors
on USB_SS_TX_P/M lines inside LM940 module.
The USB interface suggested connection is the following:
Connection for USB Interface
Interface LM940
USB Super-speed USB3.0 with high-speed USB2.0
USIM x2, dual voltage each (1.8V/2.85V)
Control Signals W_DISABLE_N, WAKE_N, WAN_LED_N
GPIO X4, GPIO
I2C I2C (optional)
Audio I/F PCM (optional)
Antenna ports 2 for Cellular, 1 for GNSS