NEO-M8U - Hardware Integration Manual
UBX-15016700 - R07
Hardware description
Page 7 of 28
Production Information
In USB
self-powered
mode, 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 would still receive 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, i.e.
VBUS is not supplied.
☞
USB bus-powered mode is not supported.
Module
VDD_USB
LDO
VDD_USB
R4
USB_DP
USB_DM
R5
C24
C23
D2
VBUS
DP
DM
GND
US
B D
evi
ce Co
nn
ec
to
r
U1
EN
R11
EN
Figure 2: USB Interface
Name
Component Function
Comments
U1
LDO
Regulates VBUS (4.4 …5.25 V)
down to a voltage of 3.3 V.
Almost no current requirement (~1 mA) if the GNSS receiver is
operated as a USB self-powered device.
C23, C24 Capacitors
Required according to the specification of LDO U1
D2
Protection
diodes
Protect circuit from overvoltage /
ESD when connecting.
Use low capacitance ESD protection such as ST Microelectronics
USBLC6-2.
R4, R5
Serial
termination
resistors
Establish a full-speed driver
impedance of 28…44
Ω
A value of 27
Ω
is recommended.
R11
Resistor
100 k
Ω
is recommended for USB self-powered setup.
Table 1: Summary of USB external components
1.4.3
Display Data Channel (DDC)
An I
2
C compatible Display Data Channel (DDC) interface is available with a NEO-M8U module 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 I
2
C 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 [2]. For bandwidth information, see the NEO-M8U Data
Sheet [1]. For timing, parameters consult the I
2
C-bus specification [5].
☞
The NEO-M8U DDCy intyerface supports serial communication with u-blox cellular modules. See
the specification of the applicable cellular module to confirm compatibility.
1.4.4
SPI
An SPI interface is available for communication to a host CPU.
☞
SPI is not available in the deyfault configuration, because its pins are shared with the UART and
DDC interfaces. The SPI interface can be enabled by connecting
D_SEL
to ground. For speed and
clock frequency, see the
NEO-M8U Data Sheet [1].
