ZED-F9P - Integration Manual
UBX-18010802 - R01
2 Hardware description
Page 29 of 64
Objective Specification - Confidential
For the ZED-F9P 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.
2.2.2 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 no backup battery is connected, the
module performs a cold start at power up.
The module integrates a DC/DC converter, allowing reduced power consumption especially when
using a main supply voltage above 2.5 V.
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
.
As long as power is supplied to the ZED-F9P module through the
VCC
pin, the backup battery
is disconnected from the RTC and the BBR to avoid unnecessary battery drain. In this case,
VCC
supplies power to the RTC and BBR.
Please connect to ground or allow all I/O including UART and other interfaces to Float/High
impedance in HW backup mode (Battery Back-up connected with VCC removed). If this is not
done HW backup current is not stable and has a very high variation.
Real-Time Clock (RTC)
The Real-Time Clock (RTC) is driven by a 32 kHz oscillator using an RTC crystal. If the main supply
voltage fails, and a battery is connected to
V_BCKP
, parts of the receiver switch off, but the RTC still
runs providing a timing reference for the receiver. This operating mode is called Hardware Backup
Mode, which enables all relevant data to be saved in the backup RAM to allow a hot or warm start
later
2.2.3 ZED-F9P Power supply
The ZED-F9P high precision receiver requires a low noise, low dropout voltage, very low source
impedance power supply of 3.3V typically. No inductors or Ferrite beads should be used from LDO
to the module VCC pin, less than 0.2 Ohm source impedance is required feeding the module. The
peak currents need to be taken into account for the source supplying the LDO for the module. We
would recommend that the source supplying the module LDO can supply 300 mA with no drop in
supply voltage.
A power supply fed by 5V is shown in the figure below. This supply is intended just for the module.
