ZED-F9T - Integration Manual
Pin No
Name
I/O
Description
51
EXTINT
I
External Interrupt Pin
52
EXTINT2
I
External Interrupt Pin 2
53
TIMEPULSE
O
Time pulse
54
TIMEPULSE2
O
Time pulse 2
Table 22: ZED-F9T pin assignment
4.2 Power supply
The u-blox ZED-F9T module has three power supply pins: VCC, V_BCKP and V_USB.
4.2.1 VCC: Main supply voltage
The
VCC
pin is connected to the main supply voltage. During operation, the current drawn by the
module can vary by some orders of magnitude. For this reason, it is important that the supply
circuitry be able to support the peak power for a short time (see the ZED-F9T Data sheet [
1
] for
specification).
The module integrates a DC/DC converter, which allows reduced power consumption.
When switching from backup mode to normal operation or at start-up, u-blox ZED-F9T
modules must charge the internal capacitors in the core domain. In certain situations, this
can result in a significant current draw. For low power applications using backup mode, it is
important that the power supply or low ESR capacitors at the module input can deliver this
current/charge.
To reduce peak current during power on, users can employ an LDO that has an in-built
current limiter
Do not add any series resistance greater than 0.2
Ω
to the VCC supply as it will generate
input voltage noise due to dynamic current conditions.
For the ZED-F9T module the equipment must be supplied by an external limited power
source in compliance with the clause 2.5 of the standard IEC 60950-1.
4.2.2 V_BCKP: Backup supply voltage
If the module supply has a power failure, the
V_BCKP
pin supplies the real-time clock (RTC) and
battery backed RAM (BBR). Use of valid time and the GNSS orbit data at start up will improve the
GNSS performance, as with hot starts and warm starts.
If V_BCKP is not provided, the module performs a cold start at power up.
If a host is connected to ZED-F9T, V_BCKP can be partially emulated by using UBX-UPD-SOS
functionality. BBR data can saved to the host and restored at startup. See
Interface Description
for
more information.
Avoid high resistance on the
V_BCKP
line: During the switch from main supply to backup
supply, a short current adjustment peak can cause a high voltage drop on the pin with
possible malfunctions.
If no backup supply voltage is available, connect the
V_BCKP
pin to
VCC
.
Allow all I/O including UART and other interfaces to Float/High impedance in HW backup
mode (Battery Back-up connected with VCC removed). See the
Interfaces
section.
Real-Time Clock (RTC)
The Real-Time Clock (RTC) is driven by a 32 kHz oscillator using an RTC crystal. If VCC is removed
whilst a battery is connected to
V_BCKP
, most of the receiver is switched off leaving the RTC and
UBX-19005590 - R01
4 Design
Page 58 of 80
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