LEA-5, NEO-5, TIM-5H - Hardware Integration Manual
GPS.G5-MS5-09027-A2
Released
Hardware description
Page 12 of 68
VCC (or VDDIO where available). An interface based on RS232 standard levels (+/- 12 V) can be realized using
level shifters such as Maxim MAX3232.
The
RxD1
has fixed input voltage thresholds, which do not depend on
VCC
(see module data sheet).
Leave open if unused.
Hardware handshake signals and synchronous operation are not supported.
For the default settings see the module data sheet.
1.5.2
USB (LEA-5, NEO-5)
The u-blox 5 Universal Serial Bus (USB) interface supports the full-speed data rate of 12 Mbit/s.
1.5.2.1
USB external components
The USB interface requires some external components in order to implement the physical characteristics required
by the USB 2.0 specification. These external components are shown in Figure 3 and listed in Table 1.
In order to comply with USB specifications, VBUS must be connected through a LDO (U1) to pin
VDD_USB
of
the module.
If the USB device is
self-powered
it is possible that the power supply (VCC) is shut down and the Baseband-IC
core is not powered. Since VBUS is still available, it still would be signaled to the USB host that the device is
present and ready to communicate. This is not desired and thus the LDO (U1) should be disabled 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
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.
Module
VDD_USB
LDO
VDD_USB
R4
USB_DP
USB_DM
R5
C24
C23
D2
VBUS
DP
DM
GND
U
S
B
D
e
v
ic
e
C
o
n
n
e
c
to
r
U1
EN
R11
EN
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 GPS receiver is operated as a USB
self-powered device, but if bus-powered LDO (U1) must be able to deliver the
maximum current of ~150 mA. A low-cost DC/DC converter such as LTC3410
from Linear Technology may be used as an alternative.
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 Ohms
A value of 27 Ohms is recommended.
R11
Resistor
10k R is recommended for USB self-powered setup. For bus-powered setup
R11 can be ignored.
Table 1: Summary of USB external components
