MAX-7 / NEO-7 / LEA-7 - Hardware Integration Manual
GPS.G7-HW-11006-1
Hardware description
Page 10 of 55
Use a proper GND concept. Do not use any resistors or coils in the power line. For ground plane design
see section 3.3.3
2.5.2
VCC_IO: IO Supply Voltage (MAX-7)
VCC_IO from the host system supplies the digital I/Os. The wide range of VCC_IO allows seamless interfacing to
standard logic voltage levels independent of the VCC voltage level. In many applications, VCC_IO is simply
connected to the main supply voltage.
Without a VCC_IO supply, the system will remain in reset state.
2.5.3
V_BCKP: Backup Supply Voltage
In case of a power failure on the module supply, the real-time clock (RTC) and battery backed RAM (BBR) are
supplied by
V_BCKP
. Use of valid time and the GPS/GNSS orbit data at start up will improve the GPS/GNSS
performance i.e. enables Hotstarts, Warmstarts, AssistNow Autonomous and AssistNow Offline. If no backup
battery is connected, the module performs a Coldstart at power up.
Avoid high resistance on the V_BCKP line: During the switch from main supply to backup supply a short
current adjustment peak can cause high voltage drop on the pin with possible malfunctions.
If no backup supply voltage is available, connect the
V_BCKP
pin to
VCC_IO
(or to VCC if not avaiable).
As long as the u-blox 7 module is supplied to
VCC
and
VCC_IO
, the backup battery is disconnected
from the RTC and the BBR to avoid unnecessary battery drain (see Figure 2). In this case,
VCC
supplies
power to the RTC and BBR.
Figure 2: Backup battery and voltage (for exact pin orientation, see data sheet)
2.5.3.1
RTC derived from the system clock; “Single Crystal” feature (MAX-7C)
On MAX-7C, the reference frequency for the RTC clock can be internally derived from the crystal system clock
frequency (26 MHz) when in Hardware Backup Mode. This feature is called “single crystal” operation. The crystal
will be supplied by the backup battery at V_BCKP in the event of a power failure at VDD_IO to derive and
maintain the RTC clock. This makes MAX-7C a more cost efficient solution at the expense of a higher backup
current compared to the usage of an ordinary RTC crystal on other MAX-7 variants. The capacity of the backup
battery at V_BCKP must therefore be increased accordingly if Hardware Backup Mode is needed.
2.5.4
VDD_USB: USB interface power supply (NEO-7/LEA-7)
VDD_USB
supplies the USB interface. If the USB interface is not used, the
VDD_USB
pin must be connected to
GND. For more information about correctly handling the
VDD_USB
pin, see section 2.6.2.1.
2.5.5
VCC_RF: Output Voltage RF section
The
VCC_RF
pin can supply an active antenna or external LNA. For more information, see section 3.4.3.2.
