UBX-G7020 - Hardware Integration Manual
Design-in
GPS.G7-HW-10003 Objective Specification Page 13 of 74
Figure 4: Power Savings using DCDC converter
For a 1.8V supply it does not make sense to use the DC/DC converter; the power savings are marginal (~5%). By
default the DC/DC converter is disabled.
The DC/DC converter has to be enabled by the Low Level Configuration. See section 2.10.2.
If the DC/DC converter is not used, V_DCDC_IN and V_DCDC_OUT must be connected to V_CORE.
The V_DCDC_IN pin may sink short term currents of up to 400mA when the DC/DC converter is enabled and the
receiver enters a Software Backup state, which can occur during Power Save Mode operation.
2.1.2.2 VDD_IO: I/O, clock and backup domain supply voltage
VDD_IO supplies all the PIOs, the backup domain and the clock domain. Thus all the PIOs comply with VDD_IO
voltage levels.
The current drawn at VDD_IO depends on the activity and loading of the PIOs plus the crystal or TCXO
consumption. Most of the VDD_IO current is consumed by the SQI bus if the firmware runs out of the optional
SQI flash.
2.1.2.3 V_BCKP: Backup supply voltage
In the event of a power failure at VDD_IO, the backup domain will be supplied by V_BCKP. Furthermore, if the
“single crystal” feature is enabled (which derives the RTC frequency from the main clock), it also supplies the
clock domain in case of a power failure at VDD_IO.
Providing a V_BCKP supply will maintain the time (RTC) and the GPS/GNSS orbit data in backup memory. This
ensures that any subsequent re-starts after a VDD_IO power failure will benefit from the stored data, providing a
faster TTFF than otherwise possible, e.g. when performing a hotstart, warmstart of making use of the AssistNow
Autonomous or AssistNow Offline functions. Thus make sure the V_BCKP supply is independent of VDD_IO
supply.
The GPS satellite ephemeris data are typically valid for up to 4 hours, so it makes sense that the battery/
capacitor at V_BCKP is able to supply the backup current for at least 4 hours to enable hotstarts. For warmstarts
or when making use of the AssistNow Autonomous or AssistNo Offline functions the V_BCKP source has to be
able to supply current for up to a few days.
If the “single crystal” feature is used, the current into V_BCKP will be increased! Make sure your backup
battery capacity is chosen accordingly to meet your specification.
If a backup supply is not provided connect V_BCKP to VDD_IO.
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