LR1110
User Manual
Rev.1.0
UM.LR1110.W.APP
March 2020
39 of 130
Semtech
•
bits 3-7: RFU
6.2.2 32 MHz Crystal
A 32MHz crystal oscillator is the cheapest and lowest power consuming approach to provide the 32MHz clock reference to
the LR1110. The crystal loading capacitance are integrated, minimizing the overall BOM cost and optimizing the PCB space.
Please refer to the LR1110 datasheet for the Crystal choice criteria.
In case of crystal operation, the VTCXO pin should be left unconnected.
6.2.3 32 MHz TCXO
In environments with extreme temperature variation, it may be required to use a TCXO (Temperature Compensated Crystal
Oscillator) to achieve better frequency accuracy. It is required to use a TCXO to use the LR1110 GNSS features in order to
minimize the power consumption required to perform an outdoor geolocation.
6.2.3.1 Description
When a TCXO is used, it should be connected to pin XTA, through a 220 Ω resistor and a10 pF DC-cut capacitor. Pin XTB
should be left open. The TCXO is supplied by the internal regulator on the VTCXO pin.
The regulated VTCXO is programmable from 1.6 to 3.3 V using the command
SetTcxoMode
( ). VBAT should always be 200
mV higher than the programmed voltage to ensure proper operation.
Figure 6-1: TCXO
The nominal current drain is 1.5 mA, but the regulator can support up to 4 mA of load. Clipped-sine output TCXO are
required, with the output amplitude not exceeding 1.2 V peak-to-peak.
Please refer to the LR1110 datasheet for the TCXO choice criteria.
Note: A complete Reset of the chip is required to get back to normal XOSC operation, after the device has been set to TCXO
mode with the command
SetTcxoMode
.
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