LLCC68 datasheet(22/106 Pages) SEMTECH

22 / 106 page

LLCC68

Data Sheet

Rev. 1.0

DS.LLCC68.W.APP

July 2019

22 of 106

Semtech

www.semtech.com

4. Circuit Description

Figure 4-1: LLCC68 Block Diagram

LLCC68 is a half-duplex RF transceiver operating in the sub-GHz frequency bands and can handle constant envelope

modulations schemes such as LoRa® or FSK.

4.1 Clock References

4.1.1 RC Frequency References

Two RC oscillators are available: 64 kHz and 13 MHz RC oscillators. The 64 kHz RC oscillator (RC64k) is optionally used by the

circuit in SLEEP mode to wake-up the transceiver when performing periodic or duty cycled operations. Several commands

make use of this 64 kHz RC oscillator (called RTC across this document) to generate time-based events. The 13 MHz RC

oscillator (RC13M) is enabled for all SPI communication to permit configuration of the device without the need to start the

crystal oscillator. Both RC oscillators are supplied directly from the battery.

4.1.2 High-Precision Frequency Reference

In the LLCC68 the high-precision frequency reference can come either from an on-chip crystal oscillator (OSC) using an

external crystal resonator or from an external TCXO (Temperature Compensated Crystal Oscillator), supplied by an internal

regulator.

The LLCC68 comes in a small form factor 4 x 4 mm QFN package and is able to transmit up to +22 dBm. When in transmit

mode the circuit may heat up depending on the output power and current consumption. Careful PCB design using thermal

isolation techniques must be applied between the circuit and the crystal resonator to avoid transferring the heat to the

external crystal resonator.

LoRa

Modem

Analog Front End & Data Conversion

FSK

Modem

Data

Buffer

ADC

LNA

Matching

LPF

LDO

DC-DC

SPI

Protocol

Engine

OSC

PLL

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