LEA-M8S / LEA-M8T - Hardware integration manual
UBX-15030060 - R06 Hardware description Page 7 of 33
Production information
The USB interface requires some external components to implement the physical characteristics
required by the USB 2.0 specification. These external components are shown in Figure 2 and listed in
Table 1. To comply with USB specifications, VBUS must be connected through an LDO (U1) to pin
VDD_USB on the module.
The USB device is self-powered, the power supply (VCC) can be turned off and the digital block is not
powered. In this case, since VBUS is still available, the USB host still receives the signal indicating that
the device is present and ready to communicate. This should be avoided by disabling the LDO (U1)
using the enable signal (EN) of the VCC-LDO or the output of a voltage supervisor. Depending on the
characteristics of the LDO (U1), it is recommended to add a pull-down resistor (R11) at its output to
ensure VDD_USB is not floating if the LDO (U1) is disabled or the USB cable is not connected, that is,
VBUS is not supplied.
☞ USB bus powered is not supported.
Module
VDD_USB
LDO
VDD_USB
R4
USB_DP
USB_DM
R5
C24 C23
D2
VBUS
DP
DM
GND
USB
Device Connector
U1
EN R11
EN
Figure 2: USB interface
Regulates VBUS (4.4 … 5.25 V) down
to a voltage of 3.3 V.
Almost no current requirement (~1 mA).
Required according to the specification of LDO U1.
Protect circuit from overvoltage /
ESD when connecting.
Use low capacitance ESD protection such as ST
Microelectronics USBLC6-2.
Serial termination
resistors
Establish a full-speed driver
impedance of 28 … 44
A value of 27 is recommended.
100 k is recommended for USB self-powered setup.
For bus-powered setup, R11 can be ignored.
Table 1: Summary of USB external components
1.4.3 Display data channel (DDC)
An I2C-compatible display data channel (DDC) interface is available for serial communication with an
external host CPU. The interface only supports operation in slave mode (master mode is not
supported). The DDC protocol and electrical interface are fully compatible with the fast mode of the
I2C industry standard. DDC pins SDA and SCL have internal pull-up resistors.
For more information about the DDC implementation, see the u-blox 8 / u-blox M8 Receiver
Description Including Protocol Specification [3]. For bandwidth information, see the LEA-M8S Data
sheet [1] and the NEO / LEA-M8T Data sheet
[2]. For timing parameters, consult the I2C-bus
specification [6].
☞ The u-blox M8 DDC interface supports serial communication with most u-blox cellular modules.
See the specification of the applicable cellular module to confirm compatibility.
1.4.4 SPI (LEA-M8T only)
An SPI interface is available for communication to a host CPU.
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