SX1276 View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
'SX1276' PDF : 132 Pages View PDF
SX1276/77/78/79
WIRELESS, SENSING & TIMING
DATASHEET
5.3.2. CLKOUT Output
The reference frequency, or a fraction of it, can be provided on DIO5 (pin 13) by modifying bits ClkOut in RegDioMapping2.
Two typical applications of the CLKOUT output include:
To provide a clock output for a companion processor, thus saving the cost of an additional oscillator. CLKOUT can be
made available in any operation mode except Sleep mode and is automatically enabled at power on reset.
To provide an oscillator reference output. Measurement of the CLKOUT signal enables simple software trimming of the
initial crystal tolerance.
Note To minimize the current consumption of the SX1276/77/78/79, please ensure that the CLKOUT signal is disabled
when not required.
5.3.3. PLL
The local oscillator of the SX1276/77/78/79 is derived from two almost identical fractional-N PLLs that are referenced to the
crystal oscillator circuit. Both PLLs feature a programmable bandwidth setting where one of four discrete preset bandwidths
may be accessed.
The SX1276/77/78/79 PLL uses a 19-bit sigma-delta modulator whose frequency resolution, constant over the whole
frequency range, is given by:
FSTEP = F----X-2---O1--9-S---C--
The carrier frequency is programmed through RegFrf, split across addresses 0x06 to 0x08:
FRF = FSTEP × Frf(23,0)
Note
The Frf setting is split across 3 bytes. A change in the center frequency will only be taken into account when the
least significant byte FrfLsb in RegFrfLsb is written. This allows the potential for user generation of m-ary FSK at
very low bit rates. This is possible where frequency modulation is achieved by direct programming of the
programmed RF centre frequency. To enable this functionality set the FastHopOn bit of register RegPllHop.
Three frequency bands are supported, defined as follows:
Table 32 Frequency Bands
Name
Band 1 (HF)
Band 2 (LF)
Band 3 (LF)
Frequency Limits
862 (*779)-1020 (*960) MHz
410-525 (*480) MHz
137-175 (*160)MHz
Products
SX1276/77/79
SX1276/77/78/79
SX1276/77/78/79
* For SX1279
5.3.4. RC Oscillator
All timing operations in the low-power Sleep state of the Top Level Sequencer rely on the accuracy of the internal low-
power RC oscillator. This oscillator is automatically calibrated at the device power-up not requiring any user input.
Rev. 4 - March 2015
©2015 Semtech Corporation
Page 82
www.semtech.com
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