MAX-7 / NEO-7 - Hardware Integration Manual
UBX-13003704
-
R09
Production Information
Hardware
description
Page
12 of 52
u-blox provides Microsoft® certified USB drivers for Windows XP, Windows Vista, and Windows 7 operating
systems (also Windows 8 compatible). These drivers are available at www.u-blox.com.
2.6.2.1
USB external components
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 3 and listed in Table 2. To comply with
USB specifications, VBUS must be connected through an LDO (U1) to pin
VDD_USB
on the module.
If 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 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.
If the device is
bus-powered
, LDO (U1) does not need an enable control.
Figure 3: 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, but if bus-powered LDO (U1) must be able to deliver
the maximum current. For the peak supply current, see a low-cost DC/DC
converter such as LTC3410 from Linear Technology.
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
A value of 27
is recommended.
R11
Resistor
1 k
is recommended for USB self-powered setup. For bus-powered setup,
R11 can be ignored.
Table 2: Summary of USB external components
2.6.3
Display Data Channel (DDC)
An I
2
C compatible Display Data Channel (DDC) interface is available with u-blox 7 modules 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 7 Receiver Description Including Protocol
Specification
[4]. For bandwidth information, see the Data Sheet. For timing, parameters consult the
I
2
C-bus
specification
The u-blox 7 DDC interface supports serial communication with u-blox cellular modules. See the
specification of the applicable cellular module to confirm compatibility.
With u-blox 7, when reading the DDC internal register at address 0xFF (messages transmit buffer), the
master must not set the reading address before every byte is accessed, as this could cause a faulty
